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I have a mobile robot that has a differential drive technique. I try to control the robot with PID controller. Is the best way for controlling differential drive robots?

If I want to compare different control techniques for this robot, which techniques do I search for?

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  • $\begingroup$ Welcome to Robotics bb0667, but I'm afraid that it is not clear what you are asking. We prefer practical, answerable questions based on actual problems that you face, so it's a good idea to include details of what you want to achieve, what you tried, what you saw & what you expected to see. Please take a look at How to Ask & tour for more information on how stack exchange works and work through the Robotics question checklist to edit your question to make it clearer. $\endgroup$
    – Ben
    Dec 22, 2021 at 14:33
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    $\begingroup$ First you should have applied your questions to a web search. Both your phrases "is pid the best control for differential drive robot" and "robot control techniques" turn up good hits. $\endgroup$
    – r-bryan
    Dec 22, 2021 at 23:24

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One way to do this easily is with a constant step controller. It's a controller that looks at the error and then just adds (or subtracts) a constant amount (usually very small). It's very easy to implement. However, it is slow to reach the desired velocity. This can be mitigated with a feed forward mechanism; when starting from 'stopped' calculate the initial control value (throttle pwm value) based on measured values for stall throttle (the throttle (pwm value) below which the motor will not turn; so this also corresponds to the minimum possible non-zero velocity). Given the target velocity, you can do a linear interpolation between min and max velocity to estimate the feed forward value for throttle. Then the constant step controller will converge quickly from a standing start. If there is a large perturbation while moving it will still respond slowly.

This differential drive robot uses a feed forward constant step controller for speed control and a constant step controller for heading control during goal to goal behavior. https://github.com/Ezward/Esp32CameraRover2 Speed control is here https://github.com/Ezward/Esp32CameraRover2/blob/3cb95bc326873d1e354887132699924332c0c7e8/src/wheel/drive_wheel.cpp#L323, kinematic pose estimation is here https://github.com/Ezward/Esp32CameraRover2/blob/3cb95bc326873d1e354887132699924332c0c7e8/src/rover/rover.cpp#L313, and heading controller is here https://github.com/Ezward/Esp32CameraRover2/blob/3cb95bc326873d1e354887132699924332c0c7e8/src/rover/goto_goal.cpp#L333 Here an example of it in operation https://youtu.be/TjE9ceNOTJE

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  • $\begingroup$ Sorry for the late reply. Step controller is the easy way for this. You're right. But it's not the best solution. I just want to ask here. Doesn't the step controller's response delay the axiom time in the wheel? Or does it not respond to the system later than PID? @Ezward $\endgroup$
    – bb0667
    Jun 27, 2022 at 7:50
  • $\begingroup$ Also, your robot is pretty good. $\endgroup$
    – bb0667
    Jun 27, 2022 at 7:51
  • $\begingroup$ It does respond slower. The feed forward helps considerably when starting from stop. The robot I am using it on is for education, so as an intro to closed loop speed control the step controller is very easy to understand and implement and calibrate. $\endgroup$
    – Ezward
    Jun 28, 2022 at 17:24

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