Update units and limits to make sense physically

[mdepp]

One of the reasons we burnt out so many motor controller boards last competition was the units used by the software and firmware were not compatible (software was meant to be in SI units and firmware was essentially arbitrary I believe). So we added some absurd scaling factors and essentially completely removed acceleration limits software-side.

We should make sure the software units and limits for the drive/arm are in SI units and make sense. This will also have to be updated in the firmware.