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Drive Motor Sizing

Drive Motor Sizing

The Drive Motor Sizing Tool is intended to give an idea of the type of drive motor required for your specific robot by taking known values and calculating values required when searching for a motor. DC motors are generally used for continuous rotation drive systems, though can be used for partial (angle to angle) rotation as well. They come in an almost infinite variety of speeds and torques to suite any need. Without a geardown, DC motors turn very fast (thousands of revolutions per minute (rpm)), but have little torque. To get feedback of the angle or the speed of the motor, consider a motor with an encoder option.

Gear motors are essentially DC motors with an added geardown. Adding a geardown both reduces the speed and increases the torque. For example, an unloaded DC motor might spin at 12000 rpm and provide 0.1 kg-cm of torque. A 225:1 geardown is added to proportionally reduce the speed and increase the torque: 12000 rpm / 225 = 53.3 rpm and 0.1 x 225 = 22.5 kg-cm. The motor will now be able to move significantly more weight at a more reasonable speed.

If you are not certain about what value to enter, try to make a good “educated” guess.

Click each link for more explanation about the effect of each input value. You are also encouraged to look at the Drive Motor Sizing Tutorial, where you will find all the equations used in this tool complete with explanations.

Input

Output (for each drive motor)


* Note: Although kg-cm is used throughout the RobotShop site, it is actually kgf-cm. Similarly, oz-in should actually read ozf-in throughout the site.

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171 Responses to “Drive Motor Sizing Tool”

  1. larry seibold

    thank you for the drive motor tool. It would be nice to save or print the results in some easy manner. I would like to know how you handle friction at the various locations, generally promotional to weight. I would also recommend a %slope time variable to separate peak power from watt-hrs.

  2. Samantha

    It would be great if it showed you the motor options after.

  3. Frank

    Thank you for this tool! Do the output(for each motor) refer to the free-run and stall torque? Or, are these values for a specific operating point?

    • Coleman Benson

      The torque value would what is required in that specific situation, and can be considered the maximum continuous torque. Based on observations and what motor manufacturers provide, the stall torque would be ~4x or 5x this value.

  4. Mitch Berkson

    Can you tell me why my result is different than yours?

    Mass: 25 kg
    Motors: 1
    Wheel radius: 0.2 m
    Velocity: 2 m/s
    Incline: 0
    Acceleration: 1 m/s2

    You get:
    Torque = 78 kgf-cm

    I get:
    Torque = (25 kg) x (1 m/s2) x (0.2 m) x (1/9.8 m/s2) x (100 cm/m) = 51 kgf-cm

    Thanks.

  5. Mitch Berkson

    Or in this simpler example:

    Mass: 1 kg
    Motors: 1
    Wheel radius: 1 m
    Velocity: 0 m/s
    Incline: 90
    Acceleration: 0 m/s2

    I would expect a torque of 9.8 N-m, but the calculator says 15 N-m.

  6. Mitch Berkson

    Thanks. The calculator and explanation are so well done that if you’re going to throw in an arbitrary number, it’s a shame not to mention it up front.

  7. Mitch Berkson

    Whoa. Now I see that you had efficiency as a parameter. Sorry about that. You can delete any superfluous comments I made.

  8. Amit

    HI! I was building an Electric Wheelchair. And i calculated the output values required for the motor using this Tool. This tool is very useful. Can you please provide the formulae used in this tool to calculate torque, speed and power? Thanks

  9. Karol

    @Coleman Benson I’ve read the tutorial provided, but I have 2 questions regarding the content.

    #1 Can you explain in details what does the efficiency value stand for, and where should I look for it.
    #2 Why didn’t you account for rolling resistance ?

    • Coleman Benson

      @Karol
      #1 There are general losses in efficiency: DC brushless motors are not 100% efficienct, nor are the gearing to which they are connected. Batteries are also not 100% efficient, and there are also losses in cabling. The value provided would be a total of these losses. Since none of the parts are known until after choosing the products, we can only estimate a total efficiency.
      #2 Honestly for simplicity, but if you can derive a simple equation using the input above, we’d be happy to add it.

  10. Rabea

    Hi. i need information about EMA actuators Application in Mobile Robotics

  11. Rabea

    Dear Coleman Benson
    could you send to me your contect

  12. Mustafa Mirza

    Dear Coleman Benson.

    I’m looking to make a hobby robot of max mass 10kg incline 30degree incline using 2 drive motors and all other parameters included the max torque your application gives me is about 300 ozf-in. i was looking to buy the pololu 100:1 or 50:1 motor set for better speeds however for 100:1 the specification lists the stall torque as 220 ozf-in. My question is how high is the stall torque supposed to be. ive read above that you said its basically 4x-5x the max torque listed by the application and in your view point which motor would be more suitable for me? the 50:1 or 100:1? please reply as soon as possible as i have a tight window to order this motor.

    • Coleman Benson

      @Mustafa Mirza If the sizing tool gives 300oz-in, the motor needs to have a stall torque of around 1200 to 1500oz-in stall torque. Neither motor would be suitable.

  13. Lars Poster

    Hi
    The incline value…if I enter a value of 20 degrees and a desired Runtime of 20 minutes, is the provided value for battery capacity calculated on the basis of the 20 minutes having been at 20 degrees for the whole period? ie.the Extreme case of 20 minutes running uphill at 20 degrees?

    lars

    • Coleman Benson

      @Lars Poster Correct. Since it’s rather difficult to estimate the percentage of time the robot will be going up an incline, the incline value is largely there for the max torque required. The battery estimate comes from the estimated current draw. Feel free to recalculate based on 0 degrees (to get an estimate of the battery pack for flat terrain) and then estimate the time it will be on flat terrain vs. incline to get a better approximation of the actual batteyr pack you’ll need.

  14. M.Ismail

    Thank you so much for this helpful tool & tutorial , but u have 1 question :
    *** If the torque is for example 1 N.m. , now i want to use 2 wheels connected together through a shaft (like simple cars) and will connect one motor only to one of them from outside the car using coupling. does this mean i need a motor with 2 N.m. so 1 n.m. per wheel OR do i need a motor of 1 n.m. and that will be divided on the 2 wheels to be 0.5 n.m. for each ??

    i.e : the torque output from the tool is it The Total Required torqur OR is it per wheel ??

    thank you in advance

    • Coleman Benson

      @M.Ismail If you still only have one drive motor per side (regardless of if you use multiple wheels or tracks), you still need to put that you have two drive motors. If you have four wheels and four motors, you put four drive motors. If you have six wheels but each set if three is connected to one side, you still need to put two drive motors.

  15. M.Ismail

    Sorry for typing mistakes in my first reply , i still have one more question:

    If i have my motor with brakes should i still worry about stall torque ?

    • Coleman Benson

      @M.Ismail Yes, and ideally you would not choose your motor based on stall but rather the maximum continuous torque the motor can provide, which is ~1/5 to 1/4 stall. The brake will simply prevent it from rotating but won’t help it move.

  16. M.Ismail

    for the motor_wheel issue : thank you a lot i understand better now .

    well the datasheet i have has 2 terms only : one is called “rated torque” which i use in selecting motors and the other is called “Peak torque” and i do nothing with it ..i simply choose the motor that has rated torque=my required torque at rated speed=my required speed ,so is this enough ?

    • Coleman Benson

      @M.Ismail “Rated torque” should be the torque at which the motor can be operated continuously for the longest period of time, so you can base yourself off that. Peak torque should only be for a few seconds.

  17. Vivek

    Really nice tool… quite practicle too…but didn’t really understand role of acceleration in the calculation. I had calculated power using rolling friction coefficient, which was overestimated. Would be helpful if you share your thoughts..thanks!

  18. Heather

    Hi so i have a weird application and I’m hoping you might be able to help me. I am looking to build an electric spinning wheel. I am looking to build something similar to a hansen mini spinner http://www.hansencrafts.com/hansencrafts/products/products_ms_ww.htm . Since i need it to operate at both high and low speeds i need to be able to adjust the rotation on the fly. I know that means i need a potentiometer and i am looking at getting a arduino uno but after that I’m stuck(I’m extremely beginner here). I’m not sure what size motor i need or whether to go brushless or not or what motor controller to get. My flyer (what i will be driving) weighs about 6 oz but will have some drag from wind. Can you help me find the correct components for my project?

  19. bhushan parulekar

    hii.. I am building an electric car.. the car should run at 60 kmph for that what should be the rpm of motor & voltage supply to the motor..the wheel that’ll be used for the car will be of dia 12″ or 14″.. thanks in advance

    • Coleman Benson

      @bhushan parulekar Building a complete, full-sized EV is a bit beyond the scope of this sizing tutorial, as well as the products offered by RobotShop.

  20. guru

    @amit, I am also planning to build a wheel chair type robot. I need some help for this project. can you shae your contact details so that I can approach you.

  21. mahmoud adel

    i want to use aservo motor with an arm to be a hammer …. is the servo suitable ? and what kind of models i need ?

    • Coleman Benson

      @mahmoud adel When the hammer hits, it may damage the servo’s internal gears and motor; you can create a sort of hammer, but the servo would need to be powerful, and there would need to be some way to absorb the shock of the impact so as not to destroy the servo.

  22. Omar Mata

    Hello, so there is one question I have. Is this sizing tool calculating just half of the robot? I have a 4-wheeled robot using just 2 motors (obviously that means 2 passive and 2 driven wheels). I’m not sure to type 1 or 2 for “# of drive motors”. Thanks in advance

  23. pavan

    we require to on/off the LC Circuit Breaker switch using DC Motor. Please suggest the suitable DC Motor for our application

  24. M.Faizan

    @Coleman
    i used this calculator and i really appreciate your work
    i am making a fire fighting robot and i want to use tread tracks with it. how will i calculate the motors required for it ??
    reply ASAP
    thanks 🙂

    • Coleman Benson

      @M.Faizan Tracks generally have the effect of spreading out the weight, but do not necessarily change the motor’s torque or rpm requirements, provided you use the drive sprocket as the wheel. Therefore if you plan to use tracks, where it asks for number of driven wheels, you can simply put two (if you plan to drive each track with one motor per side). The wheel information is according to the drive sprocket (radius). Turning in a tank is not very efficient, so you might want to drop the overall efficiency quite a bit to around 40% (since if you turn a lot in the tank, there will be a lot of wasted energy).

  25. cooper

    @Coleman
    I am trying to design and select drive motors for a project of mine with the data below:
    Mass = 25lbs
    Drive Motors = 4
    Motor Voltage = 12Vdc (will actually supply a little less to motors)
    Radius of Wheel(r) = 1.06″ (using mecanum wheels)
    Rpm = approx 110 for 1ft/sec
    Using T = Frsin(90)*16oz/in = 25*1.06*1*16oz/in = (424oz/in)/4motors = 104oz-in (I believe this is the torque to get it moving from a stop)

    If this is correct, I am having trouble selecting the appropriate motors for my application..

    • Coleman Benson

      @cooper A few values are missing for us to reproduce your results. Can you providethe output in rev/min and the Torque in ozf-in?

  26. Kishorekumar

    I came across some calculations which includes rolling friction for the force calculation, please let me know whether this calc also accounts rolling friction.

    • Coleman Benson

      @Kishorekumar No, the rolling friction is not included; there are a number of factors omitted from the calculations for simplicity of use.

  27. Jaan

    confused of this tool maybe someone can help
    I want to size motors for (minisumo 500g)
    2x wheel radius 0.015m
    voltage 6V
    if I enter this data it gives something… but nothing that I can use to find suitable gearmotor
    from https://www.pololu.com/category/60/micro-metal-gearmotors
    I understand that as robot is only 500g the traction will be issue if motors have enough power…
    so here comes question what would be minimal power of motors not to stall against nonmoving target?
    Thanks if someone can explain

    • Coleman Benson

      @ Jaan This tool cannot be used for sumo since there is an external force acting against the robot (the other robot which is trying to push yours out of the ring) which is not factored into the equations. You will need to read through the associated tutorial and understand the forces, then re-do the equations.

  28. alaa

    If I have a car have 4 wheels ,but I have 2 drive motor wheel
    In this case, what should I do

    • Coleman Benson

      @ alaa If you have two motors, each connected to their own wheel, you would enter “2” as the number of drive wheels. If you have two motors which are each connected to two wheels, it would still be “2”. If you have one motor connected to two wheels, and the other two are not driven (like a car), you would enter “1”. It all comes down to the number of drive motors.

  29. Jorge Dias

    Thanks to this, I made more progress in 1 morning than before in 1 year.
    Now that I know the specs of the motors I want, I need help to find them.
    Will someone be so kind as to tell me where will I find this: T: 14Nm P:3W I:0.25A ?
    I’m installing 4 DC motors in a medium sized cargo bot. I want it to roll 20 Kg total weight on a 15º surface, but also up some stairs at 50º. The wheels are to be 23cm high to overcome the steps, slowly.
    I simply don’t know where the motors are sold!
    Many Thanks

  30. Yogesh Patel

    My constant load is 50kg on motor can I select 12vdc high torque motor this motor rpm 60 stall torque 110kg-cm and stall current 5.1amp

    • Coleman Benson

      @Yogesh Patel The Sizing Tool is to give you an idea of the motor specs you need; if you found that’s the output and the input values are accurate, then the choice is yours.

  31. Santhosh K V

    sir i am doing 8 sem engineering i am designing a vehicle that vehicle contains 25kg. which motor, battery and solar panel requires. I am fully confused please give me a suggestion as early as possible.

    • Coleman Benson

      @Santhosh K V We encourage you to use the tool to get an idea of the torque and RPM you will need, then use that data to search for a brushed DC gear motor on RobotShop.com Unfortuantely we do not have a wide range of solar panels at this time.

  32. dheeraj

    i want motor sizing for a servo motor for a rack and pinion system..only linear..load will lie on rack and pinion to servo will traverse load left to right..load is about 1.3-1.5 kgs..12v,.46 Ah battery, the rack and pinion system will raise to an angle occasionally..and when increasing angle the load has to move left..this is total situation…btw this tool and your comments are all really helpfull..really..keep up the gr8 work..thnx

  33. Varun

    is total mass of the robot considered with assuming all motors
    mass?

  34. Hilman

    sir, i want to know my motor specification for my application. i want to build lifter project using two sprocket as wheels and one power window motor. regarding my motor as a lifter actuator, should i put 90 deg in maximum incline column to get the correct motor? and how do to measure the radius of drive wheel if i use sprocket? i mean, should i measure with the chain included?

    • Coleman Benson

      @Hilman We are not sure we understand completely. Can you create a drawing to illustrate what you are looking to create, and then create a new topic on the RobotShop Forum and share this image, and perhaps provide some additional explanation?

  35. Ricardo Kemp

    Coleman, please you can explain the formula used for all calculations ?

    In my case:

    Mass: 13 kg
    Motors: 2
    Wheel radius: 0.2 m
    Velocity: 2 m/s
    Incline: 20
    Acceleration: 1 m/s2

    Thanks
    Torque = 78 kgf-cm

  36. Newbot

    Hi Coleman. Thanks for the tool. Its really helpful. I couldn’t find (on robotshop) a motor close to what my application requires . Can you suggest what motor(s) would be an option.

    Mass: 15 kg
    Motors: 2
    Wheel radius: 6 cm
    Velocity: 1.3 m/s
    Incline: 5 deg
    Acceleration: 0.4 m/s2
    Operating time : 30 min
    Thank you for your help !

  37. Dishanth

    can you please suggest the motor to drive the 1kg of material with very less current and voltage ratings.And tell us how to decide to take the motor on that specification

    • Coleman Benson

      @Dishanth We would need to know a lot more about the application – do you mean a 1Kg wheeled robot? If current and voltage need to be low, then the gear ratio will be very high and vehicle speed very low.

  38. hugh

    Hi

    weight 50kg

    should we use 50kg or get the mass ie weight x 9.81

  39. tahir ahmed

    hello sir
    i want to rotate wheel of radius about 1.5-ft and my driven gear is also of same radius and my driver gear is 0.16-ft. this means that i need very less torque motor with high speed. So can you tell me what value i should put in upper-bar of “Radius of wheel” so i can exact calculation of motor i need..

  40. ernest seemann

    Mr. Benson, I assume you have run across the tentacle combat robot calculator and I wonder why they have radically higher numbers than your application. I assume that is because they assume a “peddle to the metal” mode of driving and assign .9 friction coefficient by default. Do does your application use friction coefficient?
    Thank you much.

  41. Biswajit Roy

    Hi Coleman!

    I was a little concerned about my design specs for a Electric cart I was building whose spec’s is as follows

    Total mass – 140 kg
    Velocity – 2.25m/s
    Acceleration – 1m/s2
    4 motors driving it on four wheels
    On a Max inclination of 15 degrees
    All terrain capable
    And the wheel radius – 0.101 m

    According to the calculation in the website, it show’s we need 300 w motors .
    But what we have noticed that an ebike needs only one 500w motor.

    Have we gone wrong somewhere?

    • Coleman Benson

      @Biswajit Roy Very good question! The electric bike uses one motor which is almost directly driven without many additional gear ratios. Increasing the efficiency of the system decreases the power required since there are fewer losses. A 300 pound robot is quite heavy, so one 300W motor operating at 24V would consume only 12.5A, which seems low. From what we can see, a common e-bike motor power rating is 36V at 15A = 540W. The bike itself weighs a lot less than the rider, and such bikes also have a maximum weight allowance. Secondly, a 300W e-Bike likely cannot work well on an incline and would struggle, or even not work at all. We have seen many reviewers and authors indicating 1000W is preferable. Last, the calculations used here are simplified (you can see the equations used in the tutorial) in order to provide ballpark estimates of the torque and RPM needed.

  42. hussain

    Helo sir i need your help little sir i am going trough a project in which i had to built a lifting system that is capable of lifting a weight of 15 kg upto a height of 10 meter so can u suggest me a sutiable gearmotor for that thanks.

    • Coleman Benson

      @hussain The torque depends on the radius of the pulley you will use. Once you know the radius, you can calculate the torque (Force x radius), then knowing the RPM and nominal voltage, you can choose a gear motor.

  43. Audrey

    Hi There 🙂

    I have the following values :

    acceleration a required = 0.05ms-2
    g (acceleration due to gravity) = 9.81ms-2
    Theta = 20degrees
    M = 5kg
    r = 0.03m
    N = 2

    When I plug this into the above, I obtain the value 0.392 for torque required per wheel. However, when I use the equation explained in the tutorial, plugging in the same values, I get 0.0294Nm per wheel – I don’t get anywhere close using the 65% efficiency rule either. However, what I’ve noticed is for the Equation T = (a + gsinTheta)Mr/N, if I put these values in, I get 0.392 as the value inside the bracket (that is the a + gsintheta part of the equation in the tutorial). Why is this? I’ve tried both degrees and radians, and it’s just not making sense to me – can you see where I’ve gone wrong?

    Best wishes

    Audrey

    • Coleman Benson

      @Audrey We do appreciate that you’re taking a look at the equations. If there is an error, we will most certainly fix it, though it will be some time before we can look into the details. For now, we can give you a bit of insight if you are prepared to do a bit of digging – the calculations used are all in HTML: view the page source and you’ll see the equations and exactly what is done. Start with the section “

      Input

      ” in the HTML. Below that, again in the HTML you will see a section “function DTMotorCalculate()” which is the start of the calculations. Just above it are the inputs and outputs.

  44. Magda

    Hi Coleman.

    Thank you so much for this awesome tool, I’ve spend hours investigating on net for something similar since I do not want to learn whole stuff behind it and just want to build the RC lawn mower.

    On the internet I’ve found that everybody uses wheelchair motors whit currents around 20A and 300W or more and I’m surprised to see that in your tool I need a lot less current and power for the 100kg mass. So I have only one question did I do this right http://prntscr.com/cinipp http://prntscr.com/cinisy ?

    Thanks in advance.
    Regards,
    Magda.

    • Coleman Benson

      @Magda We would need to know the input values. Wheelchair motors are a good and inexpensive option for medium sized robots, but keep in mind that you will most likely need to replace the controller. 8.5Nm is 1200 oz-in, which is quite powerful.

  45. Magda

    Hi Coleman.

    Let me rephrase the question. I’ve input this http://prntscr.com/cj1lm0 and got this http://prntscr.com/cj1lqr and now my question is. What motor should I use? Do I look for the motor ( or motor with gear box ) who has RPM close to 191 and stall torque larger then 105 so that I’m sure that it will handle 20deg slope and that’s it?

    Value for the current to use only for controller selection?

    Regards,
    Magda.

    • Coleman Benson

      @Magda The tool is intended to give you ballpark figures for torque and RPM. Based on your inputs, you would need a 24V DC gear motor in the 100Kg-cm (continuous output as opposed to stall) range and ~200rpm. 70Kg is a heavy robot indeed and it needs quite a bit of torque to move up a 20 degree incline. The current is an estimate based on power divided by voltage.

  46. Sou

    Hello Coleman,

    I am building a miniature Goliath tank and its track is made of ninja flex. I am thinking about buying a very small metal gearbox motor, but I am having problems selecting the best motor that will provide enough torque to move my rover. Because it is a tracked vehicle, the only drive wheels I have are the two in the back which will move the track. All of the other wheels I have are idle wheels. What would be the best way to calculate the torque needed for my motor?

    Kindest Regards,
    Sou

  47. Bruce

    Thank you so much but i still have a question that needs a direct answer, am building a robot of about 5-10kg weight and i would like to know the true specifications of motors i should use and the rating of the battery

    • Coleman Benson

      @Bruce The Drive Motor Sizing Tool is there to provide an initial ballpark figure given the data you enter. If you need something more exact, there is quite a lot more to factor in, which is beyond the scope of this tool. The battery relates to the nominal voltage you chose, and how long you need the robot to operate between charges.

  48. Giovanni

    Hi, I have a question, I am trying to build a drone of almost 3 kgs, let’s say 2.9. It must have a speed of at least 1m/s, and the radius of the wheel is 0.04 m. which motor should I choose to avoid of using a gearbox? I would like the efficency to be at 80% at least. Can you help me please? Regards Giovanni

    • Coleman Benson

      @Giovanni Motors without gearboxes are rarely able to provide sufficient torque (they spin very fast, but with almost no torque). To get a high efficiency, you need efficient gearing – try maxonmotors or faulhaber (they come at a price).

  49. Omer

    hi…nice to see this tutorial…is this still valid for stair climbing..??

    • Coleman Benson

      @Omer Very good question – climbing stairs raises some additional questions like traction / grip. You also need to determine how you want to climb the stairs: using traditional tracks or other more “creative” method.

  50. Nick

    It would be really nice if this calculator had a gear ratio input. What would be an easy way to offset the output for gearing? Could you just divide the actual wheel diameter by the gear ratio before entering it and end up with the same effective torque reduction?

    • Coleman Benson

      @Nick Consider the output torque and RPM – if you want to find the motor’s specs without the gear ratio, divide the torque by the gear ratio, and multiply the RPM by the gear ratio. We did not include this because we strongly suggest using a gear motor system with motor already connected.

  51. Sa

    Starting torque of my dc motor is 4 Nm (without using gear). Will i increase starting torque using gear??

  52. Chudi

    Hi, please what type of battery and motor would you suggest given the data from your calculator
    Input
    Total mass:25 Ibs
    Number of drive motors:1 [#]
    Radius of drive wheel:1.5 in
    Robot Velocity:1 ft/s
    Maximum incline:45 [deg]
    Supply voltage:12 [V]
    Desired acceleration: 0.254 m/s2
    Desired operating time: 2 hours
    Total efficiency: 65[%]
    Output (for each drive motor)
    Angular Velocity: 8.0000 rad/s
    Torque*:4.7796 Nm
    Total Power: 38.237 W
    Maximum current: 3.1864 [A]
    Battery Pack 6.3728 [Ah]

    Thanks

    • Coleman Benson

      @Chudi With only one drive motor, do you plan to use rack and pinion steering, or was that a mistake? Skid steer requires two drive motors. A 45 degree angle is really very steep, and the equations factor in acceleration up an incline, which may not be the case.

  53. danish

    sir i’m working on my project which is solar powered vehicle the structure is around 400kg please tell me which motor is suitable

  54. NITHIN MOORTHY

    @coleman. Respected sir, I am going to design a mobile robot for some specific applications. The details are as follows:
    1. mass= 15 kg
    2. acceleration = 0.55 m/s^2
    3. number of drive motors=2
    4. radius of wheel= 6 inch
    5. velocity = 2.2 m/s
    6. incline = 15 deg
    7. supply voltage = 12V
    8. operating time = 2 hrs
    i would be truly grateful if you could suggest me a dc geared motor which would suit my needs. I am also looking for an incremental encoder to go with that. Kindly help me please.
    Thank you.
    Nithin

  55. spinetrak

    Hi –

    great calculator, thanks a lot for this! I am going to start a first DIY toy car project, and my input parameters seem to make sense to me (except I am not sure whether I want/need 6V or 9V or 12V, so let’s go with 9V for now):

    Total mass: 1kg
    Number of drive motors: 2
    Radius of drive wheel: 0.05m
    Robot Velocity: 5 m/s
    Maximum incline: 30deg
    Supply voltage: 6V
    Desired acceleration: 5 m/s2
    Desired operating time: 1h
    Total efficiency: 65%

    This gives me the following results, but I need help interpreting this:

    Angular Velocity: 955.41 rev/min
    Torque: 3.8834 kgf-cm
    Total Power: 38.096 W
    Maximum current: 4.2329 A
    Battery Pack 8.4658 Ah

    Ok, so what is not clear to me from above is what are the specs of the motors that I am looking for?
    Does this straightforwardly translate into motors where the specs say (for each of the two) that at maximum efficiency I get

    1. torque of about 4kgf-cm / about 0.4Nm / about 55oz-in
    2. speed of about 1000rpm
    3. about 40W
    4. current of about 5A

    ??

    Next question then of course: does such a thing exist? Unfortunately, it doesn’t seem to be possible to filter your DC Brushed Motors by these specs, so it’s quite hard to go from the results to the calculator to a choice of motors (and then from there to a choice of matching motor controllers). Plus of course it gets more complicated with the option of throwing a gearbox into the mix…

    For example, with above “specs”, how about the http://www.robotshop.com/en/rs-775-motor-7000rpm-12v-7613oz-in.html which gives me (At Maximum Eff):
    Speed: 6070 rpm
    Current: 5.25 A
    Torque: 725g-cm
    Output: 45.19W
    Efficiency: 71.8%

    So if I add a 1:6 gearbox to this(???), I should roughly get
    Speed: 1010rpm
    Torque 4350g-cm
    Which is pretty close to what I need, with some headroom to go?

    PS: Yes, I realize that 1kg is maybe a bit heavy for my velocity and acceleration “requirements”, but first of all I want to make sure I understand how to go from the calculation results to specs that I can use to narrow down my choices of motors (and then motor controllers). I can then still lower the weight of the vehicle and/or my velocity and acceleration requirements.

    Thanks in advance and sorry for the long question…

  56. George

    Hello… I have to build a robot car with max velocity of 0.4m/sec and total load of 10kg. it will be used mainly for constant velocity buyt we need to control the speed with an external ESC (speed controller) if needed (from 0 to 100% speed (100% = 0.4m/sec)). I understand all the parameters except the ” desired acceleration”. I don’t know what to put there. I saw that it affects seriusly the torque of the moter. It will be used to cary video camera and cinema loads (cameras etc).

    • Coleman Benson

      @George To calculate the acceleration, consider the total time you want the robot to travel before it reaches the desired speed (v1 = v0 + a*t). In the forumula used here, it is a bit more “worst case” scenario because the robot is placed at your specified incline.

  57. George

    Thank so much for the fast response. It seems that I will need a motor of about 150-160 rpm and 7 kg*cm torque, and about 1A current. I think a battery of 9v or 12v is perfect for my project. I m thinking to use 1 brushless motor (becouse I need very low noise) instead of a brushed motor. I also need to control the speed from around 0% to 100% (100% = 0.4 m/sec, and 0% = 0 m/sec). Please can you suggest me a motor and an electronic speed controller ?

    • Coleman Benson

      @George RobotShop’s current selection of brushless geared motors is unfortunately limited, and we do not have any products to propose which would meet the specs.

  58. ReyC

    Hi. Nice calculator. I’ve calculated 2 kgf cm torque. What “torque” should I look for if I will be using stepper motors?

    I see that it is common in steppers the “holding torque”, how much of it should I look for?

    Thanks!!

    • Coleman Benson

      @ReyC Normally stepper motors are not used for propulsion systems in mobile robots. The torque of a stepper motor when in motion is quite different (lower) than the holding torque.

  59. George

    Hello.. this is a great tool. However, the output speed of a motor is with NO load or WITH load (load equal to mass) ? For example if I have a load of 3kg and need a speed of 0.5 m/sec on 0.03m wheel (car wheel) program says that we need a motor of 160 rpm. 160 rpm refers to NO load speed of a motor ? or we have to search of a motor of 200 rpm (no load) since if we put load on motor the (no load) speed decrease ?

    • Coleman Benson

      @George The torque output is under the worst case scenario of accelerating up an incline. The RPM is a “best case” to get the speed required. We suggest selecting a motor with at least the torque and RPM provided as the result. You can always choose a gear motor whose RPM is much greater and use a motor controller to decrease the RPM efficiently.

  60. ju

    Hi when choosing a motor is taking the torque calculated using the calculator sufficient or do I need to look at the stall torque?
    The torque I got from the calculator is 60ozf-in. If I want to buy a motor rated at 159.7oz-in (stall torque) would this be sufficient?

    • Coleman Benson

      @ju The torque provided as output is the continuous torque needed under the worst conditions, which would be around 1/4 the stall value. 159 / 4 = 39.75 which might be too low.

  61. ted

    hey sir I have 12 v DC motor for two wheeled mobile robot but its not pulse modulated can I drive these motors with l298 motor driver even if the motors are not pulse modulated DC motors

    • Coleman Benson

      @ted DC motors on their own would have no indication of being “PWM compatible”, except they are meant to be driven by PWM in order to change the speed and direction of rotation. The L298 motor controller is meant to control smaller DC motors which consume only around 1A under max load. Therefore be sure you are not trying to use a large / powerful motor with the L298.

  62. ted

    thank you very much sir
    i have additional question can l298 motor driver able to drive 12v ,100rpm with gear box dc motor
    or would you tell dc motors which are compatible with l298 or l293 motor drivers?
    cause sir most of the motors which are available on the market are have most of the time have voltage rating ,power rating and rpm but not the current rating

    • Coleman Benson

      @ted You need to at least be able to estimate the current consumption under load for the motor. The L298 can normally handle a maximum of 1A. The voltage and RPM alone don’t help.

  63. Ankit

    Sir,
    How do we tackle Rolling resistance in case of payloads like 700 kg ?
    Should we even consider it?

    • Eric Nantel

      @Ankit, You mean the inertial needed to make the mass turn ? This tool is intended for some DIY project so might be out of range with a 700kg payload.

  64. Rohil

    Hello Sir, I want to use motors to build robotic arms and I am finding difficulty in calculating the torque so that I can choose the appropriate motor. Since the above tool does give motor torque but why isn’t the factor of length taken into account. Torque increases with the same load placed at a higher length. How should I include length of robotic arms in this calculation?

  65. Adam

    Hi sir, how do you get the value of angular velocity through calculation? Im finding the suitable motor for solar robot cleaner’s wheels and motor to rotate brush. How to determine the exact vakue for voltage and operating time?

    • Coleman Benson

      @Adam This tool won’t help you find the motor for the brush – just for the drive wheels. You get the RPM from the robot’s velocity and drive wheel radius (refer to the tutorial for more details). The exact value for voltage is really up to you. We suggest something standard like 6V, 7.4V, 11.1V, 12V… multiples of 1.2V and 3.7V. Operating time will relate to the battery’s capacity.

  66. Adam

    Okay sir. So how do I need to find motor for the brush? And using formula c = It , why I didnt get the value same as using the calculator method?

    • Coleman Benson

      @Adam The equations used to determine the torque and RPM needed for the brush are completely different than those used to determine the specs of the drive motors. You cannot use these equations for the brush motor. Unfortunately we do not have such equations readily available.

  67. Adam

    Can you help me by providing maybe the basic of the equation for the brush’s motor; if it doesnt bring a burden to you. Hope you can help me.

  68. Adam

    Oh Im sorry. I meant the guideline and formula the determine motor spec for the brushes.

  69. sohail

    can you tell me how to calculate on load rpm of brushless dc motor theoretically?

    • Coleman Benson

      @sohail Unfortunately that is beyond the scope of this article. There are test benches on the market where you can obtain the thrust of a motor + propeller combination.

  70. Nayyar

    Sir..I have designed a robot car of weight 10 kg..And I have purchased four 12 vdc geared motor of 300 rpm,0.35kgcm torque,no load current of 60mA,load current of 300mA…Is this motor features are sufficient for driving the 10 kg robocar.

  71. sally

    what is the required motor for:
    20Kg mass
    2 motors
    4 wheel
    radius for wheel 20 cm
    power supply 24 volt

    • Coleman Benson

      @sally simply input those values into the tool. If you keep the robot’s maximum velocity at 2rpm, the motor needs to rotate at ~95-100 rpm with load. If you also keep the default incline at 20 degrees, each motor should be able to provide 1550 oz-in (111Kg-cm) or more. That’s a fairly large robot.

  72. Dsk

    I want to drive 2 dc motors,one in reverse direction,powered by a 12v battery.it is designed to handle 7kg.so kindly give the specifications(power,ampere,rpm,torque)of the motor

  73. Ahmad

    could you post the formula used for the calculation involving the motor sizing?

  74. Mihir

    Hello Sir,
    I am designing a extendible working station which will have an up/down linear motion.
    I think until now, all I know is i will meed two dc motors to lift this table up/down.
    All I really know is the maximum weight needed to lift and it is 500 lbs, so based on this,
    pls assist me on how to find a correct dc motor suitable to lift 500 lbs. i have dimensions and individual wieght of all the parts.
    Waiting for your reply asap. Thanks in advance.

  75. Vignesh

    Sir , I’m trying to build stair climbing robot….I’m useing 6.75v battery. What kind of motor should I use?

    • Coleman Benson

      @Vignesh Determine the slope of the stairs, and enough information to fill in the fields of the Drive Motor Sizing Tool to get an idea of the specs for the motor you need. Note that one issues with stair climbing is that you need the robot to always be in contact with at least two stairs, and have enough friction to climb (assuming tracked robot).

  76. Devansh

    Rather than scaling the output (Torque and Speed) by a factor of 4 to choose the DC motor, shouldn’t we scale the output by a factor of 2 considering the linear graph between the torque and speed of the DC motor and setting the operating point right in the middle of both X and Y values?

  77. nanthagopal

    Sir,we using two motor drivers with 12v,300rpm,1.76kg.cm And wheel diameter is 10cm.What is the robot vechicle speed at no load condition and with 5kg weight condition?please reply as soon as possible.

  78. Devansh

    How much margin should be taken between no-load speed and the calculated value of the RPM from the calculator?

    • Coleman Benson

      @Devansh The Angular Velocity which is calculated is with load. The no load would be (estimate) 25% higher than this. Ideally check the motor specs / datasheet.

  79. Eslam Mohamed

    Great job! that’s very helpful but,
    why didn’t you put the friction in your considerations? it would be more reliable.

    • Coleman Benson

      @Eslam Mohamed True, as well as inertia, and a number of other potential considerations. The goal is to provide a ballpark figure since it’s likely nothing has been selected prior to using this tool, and most people don’t know coefficients of friction etc. Given the feedback, it might be interesting to create a more involved calculator in the future. Appreciate the feedback.

  80. mrz

    nice one sir . but i still need your help. i have key in mass=10kg, radius=0.034m, velocity=0.025m/s, max incline=15degree, voltage=12V, accelaration=0.2m/s2, efficiency=65%, and the result i have from your calculator is angvelocity=7.0251rpm , 7.3kgfcm, and total power=0.53W. Can you show me the manual calculation with the correct formula and its respective value in case to get the same result with your calculator , please ? because i already try to understand your formula in tutorial page , but still cant get it until now.. really appreciate your help sir 🙂

    • Coleman Benson

      @mrz Unfortunately here’s not the place to write out complete calculations. We suggest you create a new post on the RobotShop Forum and follow the tutorial, writing the formula with the variables, then the formula with your numbers. We’ll be able to check there and provide feedback.

  81. apchu

    hi, i have a 500 rpm motor of 1.5 kg-cm torque and 150 rpm motors of unknown torque. just wondering if i could combine them in a robot to achieve more torque.

    • Coleman Benson

      @apchu It’s always best to use identical motors in a robot drive system. Combining different motors, even of the same speed but different torque might create problems.

  82. apchu

    thanks, i am building a off road robot for competitions. what kind of motors would you suggest, i also need help related to the wheels that i must use. this event has elements like dirt , mud, glass ,water,fire etc. what all should i take care of while building this robot.? i have used your sizing tool and would like to ask whether the torque mentioned above is stall torque or continuous torque?
    also i would suggestions as to what material i should use for building a chassis for a atv that is supposed to be built for speed

    • Coleman Benson

      @apchu The torque is what is required to accelerate up the incline specified. This should be continuous torque (torque at max power). Stall is when the motor burns. If the robot will travel over fire, then rubber will melt if exposed for too long, and glass can puncture an air-filled tire – you’ll need to consider using metal tracks with metal shock absorbers. If you really need wheels, The chassis should be fine out of aluminum. Protect the electronics inside using one or more fans blowing outward.

  83. apchu

    hi,
    i was wondering how can make the circuit connections inside the robot as to make is secure and prevent is coming off while high speeds and collisions.

    • Coleman Benson

      @apchu Wiring between electronics should be secure in some way – either using connectors, screw terminals or soldered.

  84. Samuel

    how do I calculate for velocity and acceleration?
    is it velocity = displacement/time
    acceleration =change in velocity/time?
    or is there any other method of determining this?

    • Coleman Benson

      @Samuel Those values are actually what you would like your robot to have, so you can estimate them. Yes, velocity (should be speed actually) is distance over time, while acceleration is change in velocity over time (as the units indicate).

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