ok i have a basic propeller facing the ground, im looking to make this spin so fast it generates enough lift below it to “hover” off the ground.
are there any lightweight motors i can get made for this kind of stuff? what kinds of rpms am i looking for? is it possible that a company would be selling gearboxes made for speed rather than for reduction (torque)?
any general to specific info is helpful. im making a hovercraft to float off the ground, using 3 propellers but im not sure about the motors ill need and what kind of electronics/battery with it.
I’d say a setup designed for model aircraft would give you the kind of thrust you might be looking for. How much extra weight are you going to put on it?
Some of those planes will climb straight up very easily, even without the air pocket you would probably have.
A brushless motor would be the go I recon. Bear in mind that you’ll be running this motor pretty much flat out with a reasonable load on it, so you’ll need good batteries to handle the current.
Is this the kind of info you were after?
Its just that I dont know much about RPMs since Im a servo guy. Im setting up a hovercraft actually, so it has to fly upwards and move around rather than a plane that gets a head start. Im going to use 3 of these motors on it, encased in a balsa wood chassis with a battery pack and a motor controller of course. Thats about everything the motors have to handle.
Right now, I’m clueless as far as electronics goes. I cant seem to find a motor controller that controls 3 motors. I’m still looking for the propeller blade itself (plastic or some other material) and of course the actual motors to buy here.
I have limited experience with small scale hovercraft, but from my experiments, I can tell you that you will eventually run into torque issues at some point in your project. A single vertically-oriented lift fan will impose a yaw action upon the hovercraft chassis, which must be overcome somehow. Depending on the exact method that you are using to generate your lift, this can be very pronounced, and difficult to deal with, or it can be fairly subtle and correctible.
The control issues associated with hovercraft are “quite interesting” to deal with at best, and maddening at most other times. Good luck, and have fun.
No no I said Im using 3 motors, in a triangle design. I want the motors to spin fast enough to be able to pick the craft off the ground and the be able to move around.
Still looking for:
a) the right motors
b) motor controller
c) battery pack
d) propeller blade
well, it depends on wat u’ll be running it one, and are u going to add anything else to the body of the hovercraft? (camera elctronics, receiver maybe?) wat type of battery (ni-mh, ni-cd, lipo (power to weight ratios) we need mroe details first then we’d be more than welcome to help out
Have you looked at any other rc hovercrafts? They tend to only use one propeller.
The propeller does not need to be able to lift the hovercraft off the ground by itself. Hovercrafts sit on a pocket of air that is generated by the propeller. That is why they have those skirt things around them, so you don’t need as much thrust as you might think.
The possible yaw problem that Seamus mentioned could be overcome by using only two propellers, if you wanted, spinning in opposite directions.
I don’t know if you have the equipment, or the desire to spend money on Lipo’s, but they can handle much higher current draw than most other batteries, and they weigh a lot less, but they are a lot more expensive.
If you are going to use brushless motors, you will need a speed controller for each, as I don’t think I’ve ever seen any to control more than one motor. If you were going to use 3 dc motors, you might also be better off with a speed controller for each. Unless you used the 4th channel of two dual controllers for the fan required for forward movement.
I think the main thing is that you will save a lot of money on expensive, motors etc. if you make sure there is a good air pocket under it so you don’t need the extra power.
let me clear up, i am not building an ordinary skirted airpocket hovercraft, this thing has to fly in the air. the same way a miniature helicopter does, except i plan to use 3 propellers. ill consider a lipo battery if its under 100 bucks. By controller, I didnt mean speed controller. I’ll buy motors with speed controllers attached to them. By controller I meant the general mother controller that I can program to control the motors.
If you’re looking for something that is going to fly, I hope you’re ready to put a lot of time and money into it.
I don’t know exactly what you’re after, but you might want to have a look at this: BXFlyer.
This thing is very light and has only a few components, but it is quite complex and expensive. He says that it cost him between $5,000-$10,000.
These may be different to what you were going for, but you will still need a lot of power, very little weight, and some good electronic components and software.
It might be useful to grab a copy of MotoCalc 8 which can be downloaded for 30-day trial. It is geared to aircraft of course but you can take just about any airplane configuration and then change motors, controllers, props, and batteries to get numbers for static thrust, current, and even weight of the flight equipment (by subtracting the airframe weight from the total it displays.)
Also consider that you are operating more as a helicopter (rotary wing) than a fixed wing aircraft so you might want to consider looking at the AXI hollow shaft motors and vario-prop propellers. These give you single axis collective control over the propeller, allowing you to vary the pitch rather than the RPM. That might help considerably in dealing with the rotational torque issues you will be experiencing as you develop your platform. It might also allow you to use a single 45-amp brushless controller rather than (3) 15-amp ones. Last thought is these motors/props are not really designed for big models (foamy 3D models really) so you’ll need to make your airframe very light yet strong so you may want to look into carbon fiber tubing and/or carbon-fiber reinforced balsa as structural elements.
Yeah I saw the draganflyers, they’re pretty sick. Instead of four motors I’m trying to do this with 3. The draganflyer is a perfect example of what Im trying to achieve, even though I cant imagine why they’re so expensive.
Frame
Motors
Electronics
Battery
Sensors
The frame is relatively light and sturdy, cant be expensive. High RPM motors dont cost much, I found some good ones for ~$50. The electronics might be the most expensive, cause Im looking at stacking 2 dual channel motor controllers. As for battery and sensors, they’re also relatively cheap. I dont understand why the DF is 5000 bucks.
sorry to say but your observations may be putting the cart a bit before the horse here.
you might find high-rpm is not nearly as effective as lower rpm with higher pitch rotors. that is the basic approach used to make 3D capable r/c parkflyer aircraft that hover. the value in using 4 rotors is they can paired as counter-rotating and cancel the rotor torque moments. The 3D aircraft use large control surfaces and long tail moments to overcome their motor torque aerodynamically, along with exponential scaling on their control inputs. I am not sure how you plan on doing this with 3 rotors. The physics/aerodynamics involved to solve this problem are significant if you plan on having a stable platform.
For costing rationale, the development curve to create this type of design, being capable of a pound of sensor payload in a comercial package, is a big part of the $5K pricetag, and then the low quantity likely to be sold coupled with the desire to occasionally eat is probably the rest of it.
Your best bet might be to start off small with some cd-rom brushless outrunner type motors and slowfly props. that lets you buy sub 10 ampere bldc motor controllers so your costs will be lower. consider 3 motors running in the 5A range is 15A so even using a 20C rated LiPo pack you are into 1500 to 2000mah for any amount of runtime. The battery weight alone will approach that of the 3 motors. but… you should be able to get 10-12 oz of static thrust from each motor so that will buy you some headroom for electronics and airframe weights.
I believe the first thing you are going to find is that trying to control thrust using motor RPM with the degree of precision needed to stabilize a platform in 3 axis just isn’t going to happen. the inertia in the motors and propellers is going to create a control lag time that will be difficult if not impossible to adjust out. this is why I suggested looking at the varioprops as using a servo to control the pitch will have a much quicker response. this way you use rpm to control altitude and collective to control attitude.
still there is no better teacher than experience so you should definitely give the first and lower cost suggestion a go if only to get your hands and head fully around the task. Once you get some parts and start putting them together I think you will find this is a non-trivial project, both in concept and cash flow. however if you are having fun and learning as you go that might not be all a bad thing.
I would use a capacitor vs. a battery. If you could find a light capacitor like the ones used in an AIR HOG. The things fly for 10-15 minutes and use electric motors.
Perhaps AIR HOG aircrafts would help because they are cheap and radio controlled you could pick one up at a yard sale and learn form it tremendously.
So 5K huh? What about this project is the most expensive here causing that pricetag? Bipeds are expensive due to good servos and electronics, I dont see how these flyers can get up to 5K just yet.
To be honest I’ll go with 4 rotors, no problem. I can imagine why 3 would be damn difficult. Could you also explain what the pitch is as well as a “moment”? I see this term a lot with propellers and motors and feel its important to know.
I’m not really saying that yours will be $5K, I’m saying that buying the thing off the shelf ready to go, and with who they are most likely marketing it to, $5K isn’t really much of a stretch to the imagination. How much things cost to make frequently has very little to do with how much they get sold for. How much do you think a $50K automobile cost to make, of any brand? Research that sometime if you want to feel sick about buying a new or new-ish car. Anyway, my guess is these guys are marketing to the university research crowds more than the average individual hobbyist.
Pitch is a means of expressing the angle of a propeller blade relative to the thrust axis. I forget how it’s really measured, that’s all interesting of course, but after awhile the values just sort of become like part numbers you plug into a program like motocalc to calculate thrust and currents for a particular setup. 0" pitch would be a flat plate. 8" pitch is a lot.
Moment is refering to the moment arm in calculating torque, it is the distance between the the pivot point and where the force is being applied.
I’m not sure I really ever remembered all the equations and relationships for this stuff… I know I had (physics?) classes and labs with some of this 20 some years ago… but it isn’t something I use beyond occasionally plugging numbers into someone elses program to get ballpark number on motors and props and current needed to determine how much beef I need to buy to make a particular plane fly. The info is all out there on the web of course, it’s just a matter of searching out a few good sites with the information in a format understandable and useful to your interests.
then we’d be more than welcome to help out