Weight of robot induces wheel camber

[dblanding]

I have noticed that the weight of the robot tends to induce negative wheel camber.
The video below shows how a small rotation of the motor in its mount can cause this.

IMG_4648.MOV

[dblanding]

I've seen these little yellow motors used on a host of different products, with a variety of different mounting configurations (some sturdier than others). An example of a sturdy configuration is the Adeept 4WD Mecanum Wheel Smart Car which mounts each motor on a metal bracket bolted to a thick (3/16 in.) plastic chassis.

[dannystaple]

With the shadow chassis fully assembled, the motor mount isn't moving so much, however, the gear slop in the plastic motors (FIT0450 are particularly inexpensive motor + encoder configurations) also allows the camber. The best fix really is a custom chassis using metal gear motors (like N20's with encoders), however, the current book had a stated goal of using off-the-shelf parts where possible.

There are too few inexpensive, globally available chassis that support N20 metal gear motors, with space for their encoder configurations, I definitely looked.

With the TT-motor form factor plastic gear motors, many of the rigid metal bracket types (fairly common), do not have the extra space required for the encoder collar around the motor. A quadrature encoder was an absolute requirement.

[dblanding]

You are right. the motor mount isn't moving. The motor is actually rotating within the mount. The allowable amount of this wiggle is determined by the clearance in the fit between the tiny rectangular feature (yellow) on the motor within the tiny rectangular hole in the mount.

IMG_4651.MOV

As it turns out, a little clearance here can go a long way. Tolerances are such that the wiggle on one side of my robot is more noticeable than on the other side.

[dblanding]

It turns out there's an easy fix. Just get a piece of 1/8" diameter steel wire from the hardware store, cut it to length, and stuff it into the holes of the motors. The fit will be tight enough so the wire won't be able to slide easily and the wire is stiff enough to guarantee the motors will not rotate in their mounts.