Four motors?

General discussion of using Roboclaw motor controllers
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Four motors?

Post by ridgerock » Mon Feb 25, 2019 4:37 pm

I'm looking to purchase a Roboclaw and I've had two vendors assure me that I can run four motors (one channel per side) on my fixed four wheel robot using a single Robotclaw.

Is that correct and are there any issues or challenges I should know about in doing so?

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Re: Four motors?

Post by Basicmicro Support » Thu Feb 28, 2019 9:33 am

Yes. That is correct. You want to make sure the combined current rating of the two motors are within reason for the model of the Roboclaw you will be using. The motors should be wired in parallel with each other to the motor channel.

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Re: Four motors?

Post by ChrisA » Sat Mar 02, 2019 6:21 pm

Yes, this is correct you can wire the motors in parallel. The motors will all run at the same speed as long as all of the wheels are firmly planted on the ground. But if a wheel "catches air" its motor will become unloaded and spin faster than the one that is still in contact with the ground.

What happens is that all the motors that are wired in parallel "see" the same voltage but motor speed depends on the load and the voltage. The unloaded motor will spin faster. Unusually this is not a problem unless you are looking to do precision navigation. Only one motor's quadrature encoders can be sent to the Roboclaw and if the motor with the encoder by chance is the one to "catch air" the Roboclaw's PID loop with reduce voltage and in effect stop the wheel that is still on the ground. This is not a big deal on smooth floors but outdoors you need a secondary and even 3rd and 4th way to localize the robot. (I am using an IMU and compass sensor)

If the robot is driven by a human then there is no issue at all, the human driver will see it and fix it.

But as said, electrically it works

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