Pre-load the legs to stop unwanted shivering movement

[theAgingApprentice]

The robot has issues with unwanted "shivering" motion. We are investigating a number of ways to address this issue.

• This ticket, #172, is about investigating the use of rubber bands (or other methods) to per-load the lags to stop the unwanted movement.
• Ticket #168 is about investigating the use alternate motor options like Boston Dynamics and/or MIT mini cheetah.
• Ticket #73 is focused on fixing the electrical circuit to see if that makes the shivering go away.

[nerdoug]

Re adding loading to legs: It's difficult to add loading that works no matter what position the leg is in. I did an approximation where each leg was rubber band coupled to one adjacent leg. This did reduce shivering, but it still occurred occasionally. When the legs at the ends of the rubber band were positioned close to each other, the effectiveness of the rubber band was reduced.

Shivering has also been seen in servos other than the hips. When the legs are in the "straight up" position, the knee servo sometimes shivers. In this position, it has no load, but does have the vertical shin and foot to amplify devitions.