Oldie But Goodie: Two Wheel Differential Drive Test for Sawppy the Rover’s Wheels

What’s the most obvious test after we’ve tested a single wheel on a stick?

Obviously, two wheels on a stick.

More specifically, a two-wheel chassis for testing wheel performance when driven by LewanSoul LX-16A servos.

Sawppy Differential Drive

After detents were cut in wheel drive axles and hooked back up to 180mm diameter wheels, it gave us firsthand feel of how strong the wheels can drive along the ground and… it’s a little worrying. A 180mm diameter wheel might be too big for these little servos to turn effectively.

But because a proportional Mars rover model with 180mm diameter wheels would be over a square meter in footprint, Sawppy wheels were downsized to 120mm in diameter. Smaller wheels are also easier to drive. Once the first two drive axles (with detents) were cut for 120mm wheels, they were assembled into a two-wheel differential chassis pretending to be the two middle wheels on a six-wheel rover.

This followed in the footsteps of SGVHAK rover, where we also tested our first two wheels with a two-wheel differential drive chassis. The difference is now we have an existing software package to adapt to this chassis, so we could focus on evaluating wheel performance.

These servos seemed OK turning 120mm diameter rover wheels. We’re getting encouraging torque and this chassis could drag itself along the ground at a decent speed. It looks like servo-based wheel drive is indeed going to work.

And now that we’ve validated servo driven wheels, it’s time to examine servo steering.

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