chip updates: re-design again [updates]
So this is exactly why we assembled a test leg, not that there's anything wrong with the leg just looking at it we think this may be a little complicated to deal with and it would be cooler if we could develop some sort of actuator that provides the torques we need, and then build the system around that so that's exactly what we're going to try to do today. Design that actuator.
This was kind of inspired by SpaceBok just because of how simple the leg design in this system is. We think it could be cool to do something like this as the mechanical design is simple and the platform could be cheaper. We're going to shoot for ~ 50 Nm max torque actuator! That's a great reduction of ~30-40:1 and we'll do that with a capstan-style actuator we thought of last time based on Ambidex's work.
So let's say we want to use a ~5" diameter main pulley, the pinion pulley must then be ~0.5" in diameter, we want to make it long enough for ~20 total wraps of the 1/32" cable because that will ensure the 10:1 reductions has a full range of motion. Here's the new pulley:
So we essentially are going to create a 10:1 reduction from radii alone, and then a 3:1 reduction using pullies and cables for a total of a 30:1 reduction and w/ the 80A current limit that leaves us w/ 48Nm of total torque. So far this is what we have:
That tiny shaft in the middle is the output shaft, the large surroundings is for mounting, there are two large bearings inside and the large pullies are 3D printed out of a strong material we haven't specc'ed yet. The important thing to consider is more the pullies we'll need to add to get this system working.
The bearings we specced: https://www.mcmaster.com/4390N182/
We think we might just use long 10-32 screw with spaces to bolt the motor on, and then put the (4x) bearings on that screw.
Or instead we can just use lubrication instead of bearings --> we'll try that giving us this for a final design:
We have to order a few parts but we're going to try this - have to 3D print the big gear and if we're doing something like space-bok, we may need to change the mounting holes on the output but we'll deal with that later. Now we can design the legs as 4-bar linkages or something and do kinematics like that. We'll think about robot design in the future, however.