Electronics > Electronics
Four wheel differential drive
Billy:
--- Quote from: jwatte on August 12, 2013, 02:43:39 PM ---
--- Quote ---Wiring motors in parallel will allow a low traction wheel to spin freely which will dig holes, burn the grass, throw rocks, etc.
--- End quote ---
If you have good encoders and controllers, that won't happen, as the speed will be limited.
--- End quote ---
I can't think of a way to use encoders and feedback with motors in parallel, so I assumed he was using an open loop control like RC. If he is attempting closed loop, then he either needs 4 motors or chain drive.
jwatte:
--- Quote ---I can't think of a way to use encoders and feedback with motors in parallel
--- End quote ---
He needs one encoder per motor, with knowledge of which encoders are tied to what motors.
Decide what speed you want the wheels to turn. Give PWM to motors. If the wheels turn faster than desired speed, turn down PWM. If wheels turn slower than desired, turn up PWM.
This works no matter how many control loops you're using; you'll run the same loop (with possibly different outputs for each) for each physical motor.
headrc:
So if I simply wire the motors on each side in parallel and connect them to a Sabretooth 2x60 motor controller ...I am heading for trouble?
jwatte:
If the motors have the same rating, it'll probably work out OK from a power point of view.
But, from a controller/encoder point of view, you won't be able to detect that one motor is free-wheeling and the other is stalling, for example.
Two Sabretooths? :-)
headrc:
MM...starting to wonder if I should just use two motors with transmission system for the two wheels on both sides ...although you know ...I found another gentleman on another forum doing exactly what I am talking about ...4 motors ...two on each side wired in parallel and using the sabretooth 2x60. Stated it worked great ...but he was just puttering around a yard ...not doing what I am going to do with this thing.
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