Skip to main content
shopping_basket Basket 0
Login
Give your Robot the Mobility Control of a real Mars Rover: Part 1
Bill Marshall
9
Engineer, PhD, lecturer, freelance technical writer, blogger & tweeter interested in robots, AI, planetary explorers and all things electronic. STEM ambassador. Designed, built and programmed my first microcomputer in 1976. Still learning, still building, still coding today.

Comments

June 26, 2018 07:48

Thanks for a clear and well-written article on PID. Can't do much work with rovers without these things.

0 Votes

June 26, 2018 10:15

@Reach41 Thanks! Part 2 should be appearing soon covering some practical aspects and program code.

June 26, 2018 07:48

This will work ok in ideal conditions, but try driving your robot over a rock! …… The two encoders on your wheels will give readings such that the wheels will start to fight against each over and your amps will go thru roof unless the wheels can slip at all.

June 26, 2018 10:15

@TegwynTwmffat Absolutely right. The motor drive system should be designed to climb over rocks of a specified maximum size without stalling, keeping within the PID control range. Curiosity rover is limited to about 40cm tall obstacles for safety. However the drive system did have a flaw, which has led to wheel damage. I'll talk about that in Part 3.

June 28, 2018 08:01

@Bill Marshall PS. Details of robot are here: https://hackaday.io/project/53896-weedinator-2018

July 1, 2018 19:20

@TegwynTwmffat Good grief, your Weedinator robot appears to be a 4-wheeled version of the Curiosity rover!

June 28, 2018 08:01

@Bill Marshall I addition to PID, I ended up using current sensing on the motor driver power supplies, which makes use of all the capacitors, inductors and other random wiring in those boxes to even out fluctuations. Sampling was done at 1000 Hz to get a meaningful result. After doing this, the robot quite happily climbed over rocks and craters ….. not tested it on Mars yet! …… and still cant get it to go downhill properly. Maybe you can explain how to do downhill in your next edition or 2? ...…. Thanks!

July 1, 2018 19:20

@TegwynTwmffat I assume you are using PWM for motor power control via H-Bridge drivers. Going downhill is always a problem especially with all the inertia of your robot. Usually the 'on' part of the PWM cycle applies power to the motor, but the 'off' part just lets it freewheel. The PID loop has no way of applying a brake. If the motor is shorted out when the PWM drive is shut off, it will act as a brake. Some H-bridge driver chips include this braking signal.

July 30, 2018 14:00

@Bill Marshall Thanks for reply. I'm setting up some different motors and driver for a trial ….. Maybe they will behave differently. If not, will have to try different H bridge drivers.

Related Content

DesignSpark Electrical Logolinkedin