View Full Version : [Contest Entry] A PLM mech for MW

12-29-2010, 01:40 PM
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:
YouTube - Parallel leg bioloid

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.
YouTube - Parallel leg v2

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:
YouTube - Plm V3

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.
http://forums.trossenrobotics.com/gallery/files/1/7/6/7/img_20101117_231637_thumb.jpg (http://forums.trossenrobotics.com/gallery/showimage.php?i=3645&c=3&userid=1767)
http://forums.trossenrobotics.com/gallery/files/1/7/6/7/img_20101117_231644_thumb.jpg (http://forums.trossenrobotics.com/gallery/showimage.php?i=3646&c=3&userid=1767)
http://forums.trossenrobotics.com/gallery/files/1/7/6/7/img_20101117_231654_thumb.jpg (http://forums.trossenrobotics.com/gallery/showimage.php?i=3647&c=3&userid=1767)

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.
http://forums.trossenrobotics.com/gallery/files/1/7/6/7/img_20101117_232503_thumb.jpg (http://forums.trossenrobotics.com/gallery/showimage.php?i=3648&c=3&userid=1767)
http://forums.trossenrobotics.com/gallery/files/1/7/6/7/img_20101206_203852_thumb.jpg (http://forums.trossenrobotics.com/gallery/showimage.php?i=3649&c=3&userid=1767)

The turret is bent out of one piece of sheet metal and holds the electronics, switch panel, and battery.

http://forums.trossenrobotics.com/gallery/files/1/7/6/7/img_20101217_213458_thumb.jpg (http://forums.trossenrobotics.com/gallery/showimage.php?i=3651&c=member&imageuser=1767)
http://forums.trossenrobotics.com/gallery/files/1/7/6/7/img_20101217_213533_thumb.jpg (http://forums.trossenrobotics.com/gallery/showimage.php?i=3652&c=member&imageuser=1767)
The battery bracket is on top with the switch panel underneath.
http://forums.trossenrobotics.com/gallery/files/1/7/6/7/img_20101221_151544_thumb.jpg (http://forums.trossenrobotics.com/gallery/showimage.php?i=3655&c=member&imageuser=1767)

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.
http://forums.trossenrobotics.com/gallery/files/1/7/6/7/img_20101221_151439_thumb.jpg (http://forums.trossenrobotics.com/gallery/showimage.php?i=3654&c=member&imageuser=1767)

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.
http://forums.trossenrobotics.com/gallery/files/1/7/6/7/img_20101228_212433_thumb.jpg (http://forums.trossenrobotics.com/gallery/showimage.php?i=3658&c=member&imageuser=1767)

The gun mount is installed.
http://forums.trossenrobotics.com/gallery/files/1/7/6/7/img_20101227_172849_thumb.jpg (http://forums.trossenrobotics.com/gallery/showimage.php?i=3656&c=member&imageuser=1767)

I used a hinge from a hobby shop for the hopper door. These are normally used to mount the ailerons on small RC airplanes.
http://forums.trossenrobotics.com/gallery/files/1/7/6/7/img_20101227_173408_thumb.jpg (http://forums.trossenrobotics.com/gallery/showimage.php?i=3657&c=3&userid=1767)

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.
http://forums.trossenrobotics.com/gallery/files/1/7/6/7/img_20101228_231439_thumb.jpg (http://forums.trossenrobotics.com/gallery/showimage.php?i=3659&c=3&userid=1767)

Here it is all done, waiting for electronics!
http://forums.trossenrobotics.com/gallery/files/1/7/6/7/img_20101229_124935_thumb.jpg (http://forums.trossenrobotics.com/gallery/showimage.php?i=3662&c=3&userid=1767)
http://forums.trossenrobotics.com/gallery/files/1/7/6/7/img_20101228_231538_thumb.jpg (http://forums.trossenrobotics.com/gallery/showimage.php?i=3663&c=3&userid=1767)

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.

YouTube - Mech lift and lean test

12-29-2010, 02:21 PM
Great job! I can't wait to see videos of it walking.
Jes, how many hours do you think you have spent on this project so far?

12-29-2010, 02:26 PM
Well the Aluminum took a really long time to machine. just one of the front gun supports took about an hour to cut and drill. Overall I would guess that I have something around 50 hours of build time not counting CAD. It took a really long time.

12-29-2010, 02:45 PM
Wasn't it worth though?
You've been here for at least 2.5 years. What do you think about the progress in the level of sophistication of robots and technologies on this forum?

12-29-2010, 03:02 PM
That sounds like a great discussion for a new thread. You should start one so that we can keep the discussion focused.

12-30-2010, 02:15 PM
Very great job!
Can I ask you something? Which Airsoft cannon do you use?

12-30-2010, 02:39 PM
Those are the tank guns Buell24.


12-30-2010, 05:31 PM
Yep tank guns. I bought the barrels just for the guns. Some people like to make their own though.

12-31-2010, 03:36 AM
Can you tell me which tank guns and which barrel did you buy? And where?

01-02-2011, 09:08 PM
I received my Arbotix board and got the bracket built and installed. I also got most of the electrical wired up.

The power switch is on the left. The switch on the right arms the guns.
http://forums.trossenrobotics.com/gallery/files/1/7/6/7/img_20110102_215436_thumb.jpg (http://forums.trossenrobotics.com/gallery/showimage.php?i=3666&c=member&imageuser=1767)

This shows how everything is stacked inside the turret.
http://forums.trossenrobotics.com/gallery/files/1/7/6/7/img_20110102_214213_thumb.jpg (http://forums.trossenrobotics.com/gallery/showimage.php?i=3665&c=member&imageuser=1767)

01-02-2011, 09:42 PM
That is really impressive work. I'm amazed how you fit everything in there.

01-08-2011, 10:44 PM
I found that the single tilt servo was just too weak to be able to tilt that turret so I redesigned the waist bracket to allow for two AX-12's. This new bracket also has a tilt and large cutout that allows the cabling to be cleaner and increases the range of motion significantly.

http://forums.trossenrobotics.com/gallery/files/1/7/6/7/img_20110108_233333_thumb.jpg (http://forums.trossenrobotics.com/gallery/showimage.php?i=3696&c=member&imageuser=1767)

http://forums.trossenrobotics.com/gallery/files/1/7/6/7/img_20110108_233509_thumb.jpg (http://forums.trossenrobotics.com/gallery/showimage.php?i=3697&c=member&imageuser=1767)

01-09-2011, 02:02 AM
Sweet. Dual servo torso pitch is something that I've wanted to try for a long time. I've mocked it up a couple times with Bioloid brackets, but I never actually had a proper go at it. I'm super interested in how this works out for you. Other than the added size/weight do you seeing any glaring negatives to this so far?

01-09-2011, 03:52 PM
Weight was the big downside. It does increase the length of the bracket which caused it to grab on the serial cables. That was when I decided to give it the funky angled shape. Now the cables will go where they need to, allowing me to have the full rotation of the servo.

I haven't been able to test it yet but I don't anticipate many problems.

02-01-2011, 10:17 PM
It's been a long time since I updated this thread but progress has been happening. I widened the feet to make walking a bit easier. I also redesigned the tilt bracket to allow for doubling up on the tilt servos.

It took it's first steps tonight. I still have ton of tweaking but it seems like it's going to work. Pardon the bad lighting. My office is pretty dim.

YouTube - It liiiiiives!

02-23-2011, 11:56 PM
Once again a long time since I updated but some progress has been made. The main turret code has been written and tested. I can pan and tilt finally. To answer Billy's question about the dual servos, they work a ton better than the single servo. I had to be careful about alignment but it worked great after that. I'm using a real time system with the turret where I read it's current position and then add a bit to it to move it. It seems pretty good so far.

Oh yeah, that heavy turret can cause the whole thing to topple if I'm not careful. Plus I found out it's hard to drive while videoing and looking at the robot. That caused the funky turret control in the end. The bad music was a TV on that I turned off after a few seconds.

YouTube - Walk and turret

02-24-2011, 10:12 PM
It's looking great jes1510, keep up the good work! :)


PS: Great range of elevation on the guns bud - and I loved the Nestea plunge at the end! :D Take the Plunge!

02-25-2011, 09:44 AM
Yeah, I'm gonna have to limit that range some and slow the turret down a bit. It really throws the robot around when moving at full speed.

02-25-2011, 11:01 AM
Looking good, how tall is he?

02-25-2011, 11:02 AM
A bit over 20" (not counting the antennas) when standing all the way up. It weighs right at 7lbs.

04-20-2011, 08:00 PM
Well it's been a long road and I did get done so that I could fight in Mech Warfare. My mech was slightly bent after shipping and I had more trouble with the floor than I expected. The result was that I wasn't able to turn left. Right turns worked fine, however. I suspect that the legs got bent a bit in transit. This led to me spending all day Friday working on the left turn problem. I did get it to work a bit late Friday night enough to qualify, although left turns were still finicky. My brother installed the targeting system and we called it a night.

Saturday morning I got the turret code working well enough to compete and I got ready for my first match. I was tuning the mech just before the match and found that I couldn't turn at all about 5 minutes before my first match. I discovered that a bracket had sheared in half. I was using #6 machine screws for my pivots and one of them was tightening as the mech was moving. That locked the bracket down and it tore the end off of the bracket. There was no way to fix it before the match so I went ahead and ran with a busted right leg.

The first match was against Bheka and GDubb really went out of the way to help us get the mech running well before (and even after) the match. Bheka came out of the corner and went right on the offensive. I was limited to walking just forwards and backward and Bheka was a very mobile machine. I was able to score a couple of hits with my wimpy little tank guns but for the most part the Defenders on Bheka owned the match. She did try to push me over but my large feet kept me planted pretty well.

Here is a video of the match:
YouTube - Mech Warfare 2011; Ordog vs. Bheka

The ladder was a double elimination set up but I withdrew from the second match. The broken bracket was just too much to overcome in a short time frame, even with my brother and Gdubb offering assistance.

Overall I was really happy with the performance of the mech. The PLM leg design carried the load without a hitch and the thing ran for a really long time on a single battery. The waist does need redesigning to allow better turns and I think I will attempt to add yaw servos. The tank guns are laughable with no modifications. The mods required to make them competitive are just too extensive so I'm going to ditch them in favor of something else.

04-20-2011, 08:47 PM
Jes.. it was a great pleasure meeting you finally, and kicking your bots butt wasn't bad either.:veryhappy:

Looking forward to next year..


04-20-2011, 11:37 PM
Congrats Gary and better luck next year Jes. With a year to work out the kinks, you should be a real contender next time! Nice meeting you in person finally.

04-21-2011, 12:31 AM
That last vid gdub and jes great stuff loved watching it, i feel so far away in New Zealand, but ty all for sharing your vids love it.