Single leg prototype - jumping tests

Hello!

    I hope this entry will be more exciting than the previous ones, as I'm going to show you the working prototype of Wolfie's leg. The leg was built to confirm that the actuators can withstand high torques occurring while jumping. The setup completed more than 1000 jumps on the test stand and no failures were observed so I guess after some more testing I'll be ready to continue with making twelve of these :) 

    The test stand was built from parts I had lying around. That's why it is kind of ugly. Since it's just a tool to test the actuators I didn't pay special attention to aesthetic aspects. It has a plywood base to which a 400mm long 40x40 extruded aluminum column is mounted. The 8mm rails are the remains of my old printer which got disassembled (I have built a new one - will write about that soon ;)) and so is the cart with linear bearings. The rails are mounted to the top and bottom of the column so in the middle they appear to be a bit wobbly. 

    The hip of the leg was slightly modified to fit the cart and the rest of the leg remained unchanged. It is able to operate its all 3DoFs, however, due to lack of MOSFET transistors, I am unable to operate the hip joint for now. It's a subject for another discussion but long story short I had to replace the MOSFETS some time ago as I found that the ones I was using started to fail at higher voltages due to unknown reasons. I still find this very odd and want to do a more controlled comparison between the two (SIS862DN (failing even though it is "beefier" in parameters) and SISA88DN (which is working just fine)). So for now it's a 2DoF leg, but soon I'll be making an order for powerboard parts and I'll get these MOSFETS restocked. 

    Besides I modified the cabling so that the supply cables are thinner (AWG18 compared to AWG16) and I added some twisted CAN cables for improved noise immunity. Still thinking about the best way to route the cables inside the chassis, which is somewhat linked with the powerboard itself (that I'm currently designing). 

    Actually, there's not much more to it. I derived the kinematic equations once again just to find out that the ones from here are working just fine and are much shorter (I was unable to simplify my equations). Besides I wrote a simple python code to command the trajectory (in reality it's just a few points in space) through my CAN<>USB dongle. Eventually, this came out (sorry for the image aspect ratio - it was the only way to film the test stand without revealing the mess on the desk :P):

    I'm pretty happy with the results. I managed to achieve 15cm of jump height and it could probably be more on a higher test stand and better rails. Moreover, nothing actuator-related failed which is great news. I was particularly worried about the sungear slipping on the shaft and breaking my double keyway connection or just a shaft fracture, but it didn't happen through the tests. The actuators remained cool, at around 30*C even after a few hundred jumps. The only thing that failed was the slipping belt that drives the knee. It turned out that it was not tensioned properly and slipped under big loads. This was resolved by making the leg 1 mm longer so that the belt was initially tensioned and could be tensioned even more with screw tensioners.

    Another failure, that was kind of expected (and isn't taken into account :P), was the rubber material on the foot. For the initial prototype, I have used a very soft (20 shoreA) urethane rubber that I had lying around, just to test my mold and the foot design itself. During testing, the soft rubber got squished and broke off the foot. I have to do some research for a better foot material for sure.

    Anyway, this is probably all I've got for today. Currently, I'm working on a powerboard PCB and battery pack design, so soon I'll post something about that ;)