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Servo capabilities and selection

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New ( offline )
Posts: 2
Posted: 2018-04-14 04:31 
I have 5 turning gun range target stands. These stands rotate 90 degrees. Maximum weight of each stand is 5 pounds. They are manual rotated at this time. Would like to use servos on each stsnd. I have no experience with servos. Looking for recommendations for proper servo affection. Also need assistance with controller selection. Design would need to be battery operated. Laptop available for controller. Would like ability to control each servo independently as well as simultaneously. Would also like a design that would allow for expansion.
Thanks in advance.


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Expert ( offline )
Posts: 837
Posted: 2018-04-16 10:53 
Hi,

First thing to do in order to choose a servo that will fit your application would be to calculate the torque capacity needed from the servo to easily rotate the stands without stalling.
Torque is a measure of how much a force acting on an object causes that object to rotate, it is expressed as the weight of the object to rotate multiplied by the distance from the pivot point to the point where object's weight acts.
Its SI Unit is normally in N.m (Newton.meter) but in the world of servos, you can find the torque expressed in Kg-cm or Oz.in.
For example, if you are planning to rotate 5 pounds at a distance of 5 inches, you would need a servo that has an operating torque of at least 80 Oz.in (or about 5.76 Kg-cm).
Next thing to think of would be if you want to work with regular RC servos or Smart servos. Here is a nice blog article that explains the difference between both.
The choice of the controller will be based on which servo you will be using. This blog article will provide you useful information on how to choose the servo controller that will work in your setup.

Here is a link to our RC Servo Motor Controllers for your reference. For example, if you will be using 5 servos to rotate your 5 stands (one servo for each stand), you can look at the Pololu Micro Maestro 6-channel USB Servo Controller.
For power, this will also depend on your choice of the servo. If you chose to use RC servo, these servos usually work with 4.8V-6V or 6V-7.4V.
Smart servos voltage rating depends on the brand. Dynamixels usually work with 9V-12V and Herkulex servos with 7.4V-9V.
It is also important that your power supply is able to provide enough current for the servo to operate without issues (look at rated current or approximate rated current by 25% of stall current).

Hope this helps,

_________________
Brahim Daouas, B. Eng
Robotics Specialist - Electronic

RobotShop inc.
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New ( offline )
Posts: 2
Posted: 2018-04-16 14:33 
Thanks for the information. I estimate a torque of 96 oz. I think RC Servos would work fine and the Pololu Micro looks like it would work fine. Is there a remote option for control. The firing line would be back as far as 50 yards. I forgot to mention that this would not be installed on a permanent range, so running cables to leave them installed is not an option. A remote control would give me the ability to control the targets on the fly, rather than always running a preprogrammed solution.

Thanks
Marc


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Expert ( offline )
Posts: 837
Posted: 2018-04-18 11:36 
The Pololu Micro Maestro 6-channel USB Servo Controller can be interfaced with a microcontroller as indicated in page 68 of its dataheet.
Therefore, it can be controlled wirelessly with, for example, an Arduino UNO and an XBEE Wireless Module. You also might need an XBEE shield for the Arduino Board like the DFRobot XBee Expansion Board.
Another option might be to use a Wireless Servo Controller like the Wireless Servo Control for Arduino Nano and NRF24L01 that uses the NRF24L01 Wireless Transceiver and an Arduino Nano Board.

_________________
Brahim Daouas, B. Eng
Robotics Specialist - Electronic

RobotShop inc.
Putting Robotics at your service!™
www.robotshop.com

Lynxmotion
Imagine it. Build it. Control it.™
http://www.Lynxmotion.com


 

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