Robot won't go forward or backward

[dodgyhair]

Hi, my son and I have just built the robot kit and everything is working really well apart from it won't go forward or backward. The wheel servos work - they will turn it left and right when the joystick is moved in those directions, but nothing happens when the joystick is moved forward or backward. I've tried controlling from a laptop and ipad but same result. Even when running motor_test.py it does everything except move forward and backward.
The SD card was build 'manually' from your instructions. The camera and camera servos work fine. Any ideas?

[Alan]

Hi there,

Welcome to the forums.

That's an odd problem, usually the motors work well, or not at all.

How are you powering your robot? A lot of problems can arise from that area.

Also, can you check that the switch on the mini driver is set to on? If you're powering your robot from a USB battery pack then the mini driver may get enough power from the Pi to move the servos and the motors very slowly, but the switch needs to be on to give power to the motors.

Regards

Alan

[dodgyhair]

Hi, thanks for the prompt reply.

I am using the USB power bank to power the robot. It has at least two thirds charge when I am testing it.

The mini driver switch is definitely set to 'on' (and the voltage jumper to 5v).

Apart from the forward and back, the wheels seem to turn fine. Here's a vine of the robot doing part of the motor test: https://vine.co/v/OA2naB00Zb6

[Alan]

Hmmm,

Ok my guess would either be a problem with the motor wiring or perhaps a dodgy mini driver board. I think that I've had similar behaviour in the past when I had both of the motors connected both to ML and MR (as opposed to on connected to ML and one connected to MR).

To test the wiring, I would first disconnect both motors, then just try to wire up the left motor to ML, it should go forwards when you push forwards or right on the web interface joystick, and backwards when you push backwards or left.

On a lower level, both the turn commands and drive commands use the same routine to set the motor speeds in the range -100% to +100%, so in theory, if turning works driving forwards should work.

Regards

Alan

[dodgyhair]

Success! As usual, it was a simple error (on my part). When I fed the wires from the motors through the chassis to the board they got mixed up so I had one wire from one motor and another wire from the other motor going into the same terminals. When I did the test you recommended neither motor worked which gave the game away. All good now!
Many thanks for your help. You have a really great site and great service.

[Alan]

Fantastic. Glad you're up and running, have fun with the robot.