Let's Make Robots!

Mr Basic - drive train too stiff for motors to move...

I just picked up a Mr Basic kit from one of those free shipping Chinese stores. It's gone together OK, but the drive train is really stiff and the motors can't move it (even on 6xAA NiMH). Any tips?

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

I will check this on Monday when I am back in the office.

In the meantime, check that your drive shafts are straight. When you tighten the grub screws on the shaft links you need to make sure the shafts stay relatively stright.

OK, one last late night take apart and I've made a little progress. I took everything to pieces and then left put it back together without any of the shafts, so I could check the alignment. I then twiddled by hand an appropriate sized drill bit (forgive me!) in all of the holes, using it both to make sure that all of the holes were lined up, and also removing any burrs along the way. Then I systematically rebuilt things, making sure that every shaft and gear pair had a little grease. I've ended up with a working chassis, and although it's not what I'd call smooth, the motors are coping.

I think the issue is what you said, OddBot - the straightness of the shafts. The couplers are making for a very slight kink on each shaft. Maybe my taking it apart and reassembling has ended up pairing the shafts and couplers that make the best matches? Whatever - onwards and upwards. I just did a basic test with an Arduino and Adafruit Motor Shield - it's alive!

I built my basic bot, minus the sweep servo for the ultrasonic rangefinder. Looks cute; doesn't work. :( The drivetrain is too sticky to allow any kind of left-motor-forwards/right-motor-backwards type steering. Woe is me. Time for a new chassis?

I'm not sure where your problem is but looking at your motor driver I'm not sure you would get it working anyway. The Mr. Basic kit has a Stall Current of about 2A per motor.

Oof - that's a lot; that shield can only handle 1.2A. Better with something like this?

have you applied any lubricant?

 

A little, yes. There was a small ziplock bag(!) with grease in it. It doesn't feel like it's made a difference - there's some misalignment somewhere. When I reassembled it I checked carefully at each stage to see where the tightness was being introduced, but I'm not really any the wiser as it seems to be a cumulative thing. Starboard's a fair bit better that Port. The gearbox unit spins smoothly; installing the rear axles makes things a bit tighter; coupling the front drive shafts adds a fair bit of tightness, and then the front axles seem to introduce the rest of the problem.

Maybe I should go 2 wheel drive? :o)

Thanks, OddBot. I took it apart and reassembled it. It's slightly better, but still not working. I took a few photos - would you mind taking a look to see if anything looks wrong?

If the drive train is that stiff then you have not assembled the kit correctly. There are one or two parts that are easily put in the wrong way that can cause your problem. Pull it apart and assemble it again.