Next large robot

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  • Machining more parts, lots of soldering, and starting to re-assemble the legs with the upgrades installed. It’s going to be several more days to finish this up but then I should be able to start testing 2 legs together and see if the gait engine works right, ie both legs move the right direction. Of course each leg has to be calibrated first which is a tedious project. Here are some photos of progress.
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    These are the arms that are used by the coxa encoder to move the shaft as the coxa motor moves. It’s a slightly different design from the test version but it should be more reliable. The test version had issues with the spring wires popping out of the arm, this solves that issue.
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    These are the encoder housings with the wiring harness installed.
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    These are the coxa encoders mounted. Mods to this part included drilling the hole for the encoder and cutting 1 inch off the back of the mount to allow more room for the sensor plugs and wires that are mounted directly behind the piece. Some wires were getting pinched and the extra length wasn’t needed on this mount.
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    Here is a fully wired encoder in its housing. The other encoders still need their shafts cut down to 1/4” and soldering the wiring harness to the encoder. Initial calibration is connecting to a program to determine the output value to make sure the output doesn’t cross zero in the expected rotation range.
  • Testing the encoders with a simple calibration program now that the electrical connections have been made. Out of 15 encoders, 5 did not work at all. On a whim I swapped the CS and CLK lines and the ‘failures’ started to work correctly. Not sure how I could have made that serious a soldering mistake on 30% of the encoders, I started cutting the CS and CLK wires and swapping them. I got down to the coxa encoders and just by chance noticed that some of the pre-wired connectors that I have been using have the 2 outside wires on the connector swapped! So when I was soldering and using the wire color to match up to my schematics, the wires were not correct at the connector end. That explains some of the other issues I have had using these connectors in other locations, I never thought to look at the order of the wires in the connector itself.
    Now that’s sorted out I can continue with the initial calibration and start installing the encoders.

    Bob Sweeney
  • I had to throw away the coxa encoder arms that I made earlier. When I installed the arms I found several problems with the new design including the fact that they were almost impossible to install in the space available. Back to the drawing board and I reduced the length of the arm down to 1.5 inches and increased the width of the slots on the ends of the arm to 0.125 inches. I also drilled 2 more holes in the support plate to allow a hex wrench easier access to the screws that hold the springs to the movable portion of the leg. The screw connection for the spring may need some adjusting also, the spring is sitting at an angle and it should be level, may make some custom spacers to elevate the point where the springs connect to the leg. The springs I am describing are custom springs made using 0.54” music wire that was wound on a jig to get the correct spring length and connectors for the hold down screws.
    I also mounted the femur and tibia encoder housings on one leg. I found that I was getting some interference from the head of a bolt that didn’t allow the encoder to turn smoothly. That was fixed by adding a thin washer on the encoder to push the encoder shaft away from the bolt head. Also the friction fit discs that slip on the encoder shaft had to be discarded as they were too thick. I figured it would be faster/easier to use the lathe to fabricate new parts rather than figuring out how to reduce the thickness from 0.25 to 0.21 inches.
    Leg # 2 is now put back together, will be working on finishing up the other legs now that I have good measurements for the needed parts. The remaining legs should go a bit faster.
  • DiverBob wrote: »
    ... The springs I am describing are custom springs made using 0.54” music wire that was wound on a jig to get the correct spring length and connectors for the hold down screws....

    DiverBob, is that decimal in the right place? Half-inch music wire? Post a picture!

  • DaveJenson wrote: »
    DiverBob wrote: »
    ... The springs I am describing are custom springs made using 0.54” music wire that was wound on a jig to get the correct spring length and connectors for the hold down screws....

    DiverBob, is that decimal in the right place? Half-inch music wire? Post a picture!

    Oops, you are right, it should be 0.054 diameter! Half inch might be a bit hard to bend by hand...
  • I got leg #1 mechanicals updated and attempted to install the leg on the body. Unfortunately I discovered that the wiring harnesses I created for the encoders is about 2-3 inches too short. I got the bundled 6 wire cable length correct but the connectors were too short to reach the sensor plugs. Thats when I remembered that I cut the plug wires shorter by about 4 inches. So to get around this SNAFU that I created for myself, I wanted to see what the easiest fix would be. By swapping the positions of the sensor plugin board and the motor power board I was able to get the plugs close enough that I could plug in the sensors. The disadvantage of this was that I could see that the motor wires could potentially interfere with the coxa encoder movement, plus I was worried that the encoder wires are still tight and coxa movement could damage the wires. All the other potential solutions I thought of were either fairly extensive or too complicated. So the best answer I have is to go back and solder in the extra length of wire that I cut off. So that is about 120 solder connections to make again..... Unfortunately this was a self imposed problem this time.
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    3264 x 2448 - 1M
    3264 x 2448 - 1M
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