I have been asked several times to do a detailed build thread for my first biped. The robot is going to hopefully be a contestant in the 2011 Mech Warfare competition.
I had never built a biped before and decided that I wanted to do something "different". Once the parallel leg thread came around on the forums I realized that this was something that I could experiment with. I knew that I wanted to build a reverse knee walker and figured that the parallel legs gave be the best chance for success. I also realized that the hips and ankles were going to see a ton of stress so I doubled the servos in those areas.
I first prototyped the legs using the stock parts in the Bioloid kit. Here is a video showing the initial tests using just the Bioloid parts and a CM5 for control:
[ame="http://www.youtube.com/watch?v=nTarX-_XYgU"]YouTube - Parallel leg bioloid[/ame]
I then built the legs using the same dimensions as the Bioloid kit. This later turned out to be way too long and the joints had to be shortened. This video is of the testing using the first version of the legs using sheet metal. Note that the joints use bearings from Lynxmotion. I found that these bearings have the same dimensions as the plastic hubs from the Bioloid kit.
[ame="http://www.youtube.com/watch?v=fv3aK-DR8dg"]YouTube - Parallel leg v2[/ame]
All sheet metal was designed using QCAD under Linux. I then used Darkback2's method of construction. The CAD was printed out and glued to the sheet metal. All holes were drilled using a drill press. I then cut the parts out on a bandsaw using an 18 tooth blade. Inside cuts were made using a scrollsaw and a 20 tooth blade. The outside rounds were sanded to shape using a bench mounted belt sander. All bends were done on a box brake I found at Harbor Freight. This process takes a really long time but I was really happy with the results.
This test proved that the legs really had to be shortened since they were going to be way to long. I decreased all of the dimensions and rebuilt them out of 0.065 sheet aluminum. This is version 3 of the leg with the new aluminum and shortened dimensions:
[ame="http://www.youtube.com/watch?v=wbYwv2HToGA"]YouTube - Plm V3[/ame]
I finally had something that I was fairly happy with. The only other change to the final version was to lay the ankle servos on their side and increase the size of the feet.
Unfortunately, I did not have all of the electronics on hand so from this point forward there is no video and I have not been able to test it while walking.
Here is better detail of the leg joints mounted to the new hips. These use the old feet that were later changed. Sorry for the messy desk. A clean desk is one that is seldom used.
The pan and tilt servos mount on the top of the hip bracket. I am still a bit nervous about using just one tilt servo since the turret turned out to be kind of heavy. I may have to redesign this bracket once the electronics get here and I can test the performance.
The turret is bent out of one piece of sheet metal and holds the electronics, switch panel, and battery.
The battery bracket is on top with the switch panel underneath.
I was a bit worried that the guns would wiggle due to the long moment on the barrel so I made some front supports to hold them in place.
Here are the individual pieces of the gun mounts and hopper for ammo. The hopper is built out of 0.032 aluminum and wraps around the gun mount so the hopper is part of the main structure. There is also a small ramp inside the hopper to guide the BB's to the feed for the gun.
The gun mount is installed.
I used a hinge from a hobby shop for the hopper door. These are normally used to mount the ailerons on small RC airplanes.
The same was done for the other side except the parts are mirrored. This also shows the side plates that will support the target panels on the sides.
Here it is all done, waiting for electronics!
Edit: I decided to shoot a quick video of the Mech leaning and lifting a leg. I had to use a CM-5 attached to a computer to send the poses. This was just a test to see if it would even lift itself. I apologize for the bad quality of the video. I had to shoot it with my cell phone while running the computer.
[ame="http://www.youtube.com/watch?v=heTNereAvkQ"]YouTube - Mech lift and lean test[/ame]