chip updates: mechanical upgrades/fixes [updates]
So over the past week of testing, we've either created or noticed some issues with chip's mechanical system. Issues we can now fix!
issue one: the screws holding in the lower leg to the bracket keep coming un-done
Here's a problem. This tripod leg is secured to the rest of the leg using a single 1/4-20 screw which isn't necessarily a problem. The problem is this thing keeps coming un-done/loosening.
So initially, I looked at this and the only idea that came to my mind was thread-locker. However, I remembered something Salem Ali (our old MechE lead for solar car taught me). I can use 1/4" spring washers! This exerts outward pressure on the bolt head and the face increasing the effective "pre-load" which will increase the effective friction which will reduce the chances of it slipping.
I'm going to do this over thread-locker because thread-locker may not come out and what if we want to service this leg or something.
issue two: standoffs bending and shearing
The images above show, on the rear legs especially because of the added weight/force on them, the standoffs holding the motors onto the leg itself bending and shearing off. That was the problem yesterday when we heard the crack sound, two of the standoffs actually broke. So the solution to this is we don't actually want to use the standoffs we want to bend the steel plate around the motor and directly secure it to the motor like that.
This is likely a much better method for securing the motor to the leg, at least for the lower leg, because now the plate acts as spring-washer for the bolts securing the plates to the legs, and the plate is support the motor not just via the standoffs, but by holding against the motor's mount as well. See the compression in the figure above.
issue three: the feet slipping (fixed in previous post)
So in this case, we won't go into too much detail since we posted about this, but we added some straps of yoga mat tightly to the bottom of the feet. These were duct-taped on. The yoga mats allow for some extra grip on the feet.
- 1/4-20 spring washers
- New gearbox base (broke the old one)
- 10-32 Standoffs