I am a disabled outdoorsman who really enjoys to shoot firearms (shortmagzone.com/DisabledSportsmen/Equipment/HuntingShooting.aspx). I am bound to an electric wheelchair and currently have a shooting platform that was made by my uncle that runs off of my wheelchair’s 12 V battery. To control elevation (up/down)and windage (left/right) the platform uses a DC motor, threaded rod and nut, and uses the Bardac 200XLV 4-Quadrant DC Servo Drive (bardac.com/pages/products/servo.html) to control each DC motor’s speed/velocity/acceleration and direction and costs about $300 apiece. I use a two axis joystick (p3america.com/pp/811.htm) to control the motor controller/driver by regulating the amount of current to each controller.
My cousin and I are in the process of redesigning the platform to use a linear actuator to control elevation and a stepper or servo motor to control windage. A rough sketch is attached that will give you an idea of what I’m trying to accomplish.
Using Phidgets’s linear actuator, mini joystick, 8/8/8 interface kit and 1 Servo motor controller, I have tried to create an open loop system programmatically even though it is meant to be a closed loop system. I have somewhat succeeded, but I’m not happy with the result. I’m not needing to do any calculations or anything so I don’t believe I really need a microcontroller.
I guess what I’m looking for are some opinions on what motor controllers/drivers, linear actuator (for elevation), stepper/servo (for windage), and joystick I should use. I need to stick with an open loop system, so I’m thinking I need to use a H Bridge motor controller/driver, but I’m not sure which ones as there are quite a few available with the wrong little variances.
These are the pieces that I’m currently thinking that may work for what I’m trying to accomplish:
Motor Controller/Driver
Sabertooth Dual 5A 6V-18V Regenerative Motor Driver robotshop.com/ca/Sabertooth-2x5-en-1.html
*Using the non-differential drive analog option
Basically, part A sits on top of part B. A is attached to the shaft of the DC motor. When you move the joystick to the right, part A moves to the right, if the joystick moves to the left, part A moves to the left. Consequently, the DC motor is permanently attached to part B. Sorry, I didn’t have a front or top view. I’m working on the mechanical drawings for it.
I’m not totally sure about that. I’m thinking that the total weight A will have on it, at absolute maximum, would be 50 pounds. As for RPMs, I’m thinking something on the low end thus given me more torque. I’m only looking to move it +/- 45° off of center. Any movement back at the shooter is magnified many times over at the range at which the target is. My current rig uses 24 rpm DC motors with an acme threaded rod. I’m not quite sure what the thread specs are for that, however.
In your opinion, what’s going to be the better motor for accuracy and durability, spur or planetary in which one of your motors do you recommend? It looks like you have quite a few. Also, do I need to run power to the joystick and motor controller or can I just power the motor controller?
OK, thanks for the clarification on the motors. I was looking through the documentation for the sabertooth and it says that it can power a “receiver” and 2 motors. I was just assuming that joystick and receiver can be used interchangeably. In the end, I will probably have some circuitry that takes power from my wheelchair 12 V battery and powers that joystick, motor controller that powers both the actuator and DC motor, and a small linear actuator that pulls the trigger through a bite switch.
Before I start laying down some money, are we sure that the Sabertooth will work in an open loop so when that joystick springs back to center, the motor will stop moving? For example, say I move the joystick on the Y axis (elevation using the actuator) to say position 100 and release the joystick, the actuator will stay at position 100. When I slightly move the joystick off of center, in the positive, the actuator creeps to position 105 and when I release the joystick the actuator stays at that position. If I move the joystick in a negative direction, the actuator moves from position 105 to whatever position the joystick is at.
Sorry to rehash it. I just want to be careful/cautious. Thanks again for all of your help. It’s been great!
This would be the primary concern, since actuators are not meant to take such a violent and sudden force. The actuator and controller you selected seem fine, but can you elaborate on how you intend to use the “windage motor”? You may want to use the R/C version of the Sabertooth and either the 2 Servo Joystick Controller or the ServoCity Joystick Controller.
You should not have the shaft of the motor (whichever you choose for the windage motor) support the load; use bearings. The inertia required to stop a 50 pound load is not insignificant either. Consider a low RPM spur gear motor or planetary gear motor.
Planetary gears are more “advanced” than spur gears; they are quieter and more efficient, but cost more to produce and are therefore more expensive. You need to select one based on the torque required, RPM and also nominal voltage. The Joystick needs to be powered, as do the motors; if they all operate at the same voltage, you can in theory use one battery so long as it can provide the necessary current.
When in doubt, it’s best to be cautious and read the Sabertooth manual first.
1500ms pulse is neutral, which corresponds to the joystick’s neutral position; 2500 is max speed forward, 500 is max speed reverse.
The Sabertooth does not offer closed loop (it would be much more expensive).
