Introduction: Six Legged Walker With Strong Joints!

Picture of Six Legged Walker With Strong Joints!

https://www.instructables.com/id/Hexabot_Build_a_heavy_duty_six_legged_robot/

The above linked instructable is awesome. It's cool, and the joints it uses (holes drilled in box tube) will egg out very quickly and degrade with time.

So, I decided to beef it up, so mine wouldn't end up crippled. I followed the instructable pretty well, but used different motor mount configuration, used the wheelchair's motor controller, and made my eccentric drive plate out of steel (free) instead of aluminum.

The theory in my telescoping sleeve bearings is that there is strong steel in the middle (bolt), and less strong steel on the outside (pipe/box tube), with brass and grease inbetween. This brass/grease will decrease wear on the steel components, and take up the slop.

This is a work in progress, to be updated as progress comes along. 

Step 1: Measure Your Bolts.

Picture of Measure Your Bolts.

Get a micrometer and measure your bolts. The issue here involving the micrometer is that often the threads are slightly wider than your bolt size, or slightly smaller. For instance, my 1/2 inch bolts have .495 or so diameter on the bolt, and .485 on the threads. this is all basically meaning "use 1/2 and pack with grease". The measureing of everything comes more important later.

Your top end bolts will probably be smaller, I used 3/8th up top, and 1/2 for main drive.

Step 2: Get Some Pipes!

Picture of Get Some Pipes!

Now get some weldable steel pipe that has a slightly larger ID than your bolt's OD. Then get some brass tubing or pipe that will make up the difference. Make sure (DAMN SURE) that your pipe doesn't have welds internally, or else you are going to have to get more pipe. 

i got lucky with my top end, and have 3/8th bolts, with 13/32nd or 27/64th inch brass tube, and a 1/2 inch OD steel tube that fit really well. At this point of buying things, go around with your bolts, and just try different combinations to see if you can get lucky. If you don't get lucky... Well then.

I didn't get lucky with the main drive. I got the 1/2 inch bolts, I found some weldable steel pipe with supposedly 1/2 inch ID, (which was a good bit larger, around 1/8th or 3/16th larger), and then got some brass pipe with a 31/64 ID, and a large OD. Measure accurately with some calipers, chuck that brass on the lathe, and go to town.

Step 3: Drill/overbore the Holes, Insert Pipe, Weld.

Picture of Drill/overbore the Holes, Insert Pipe, Weld.

 So if you've made the walker already (like I did), then you overbore, if not, then drill out to slightly larger than the OD of your pipe. If you drill to the size of the pipe, you'll need to hammer in the inserts (as I did on the smaller/top end ones). 

Wash everything, then weld away. I TIG'ed everything, because the tolerances were tight, and I wanted it to be strong. A very good welder could use MIG... I don't think I could. If you don't have tig, perhaps gas welding or stick would be the next best? It comes down to you wanting a good weld with minimal excess fill sticking up top to grind off, then sand it smooth so it doesn't interfere with the washers. 

If you get much metal slumping inside the pipes, you may need to bore out the holes. If so, i'm sorry, because that will suck. Just use a lot of cutting fluid. 

Step 4: Add Offset

Picture of Add Offset

 The front didn't line up, so I needed to make an offset, to avoid having a 4 inch stack of washers. 

Step 5: Make the Brass Inserts.

Picture of Make the Brass Inserts.

 I had to lathe down some brass for the larger bolts. After that, sand them very smooth, then assemble everything, and cut them to fit. At this point, don some latex gloves, and grease everything.

This is somewhat of the moment of truth. As it turns out, truth wasn't good for me. My 31/64th id (.485ish) didn't jive well with the .480 bolts, so I lubed them up, and pressed them together with a vice. All the wear is going to be on the outside, apparently. 

Step 6: Get a Lift.

Picture of Get a Lift.

 Find something to raise your little dude off the table. With the motors, this thing is heavy. Save your back. Make sure to have some diagonal connection as well, so it doesn't tilt when you put on things. 

Step 7: Nylock Is for Suckers.

Picture of Nylock Is for Suckers.

 Man up and use a lock nut. What's a lock nut? When you put another nut after your load-bearing nut, and counter-tighten them. You only need 3 threads of engagement to get a good bite, so you don't really have to have excessively long bolts. 

Also, don't be like the original hexabot dude. Put your bolts from the outside in, so that you have minimal clearance past the legs themselves. The caveat is the center bolt, which must be facing out. I'm thinking about  chopping, drilling, and safety wiring that one. 

Step 8: Assemble, Refactor, Rework.

All the legs are done! I jumpered the motors to a battery and made it scramble in a circle! I just need to figure out how I'm going to put together my control circuit.

Current theory is to re-use the banks (8 per motor) of IRF3205 MOSFET's to change a 

Comments

r570sv (author)2010-04-28

I like!  I'm planning on sometime similar in size this summer.  Can't wait to see what you end up with.

Did you use the standard diminesisons for your plans or did you modify them?  To get the increasing the length of the legs makes the body waaaay to big for a standard sized garage. 

seraphus (author)r570sv2010-04-29

 Hey... So I've been not updating this, because I've basically come to the conclusion that my design was fundamentally flawed. No matter what I do, the sleeve bearings are being consumed, my motors are mismatched (one side is much stronger), and it has a tendancy to shatter the cast urethane feet I made for it.

That being that, I'm storing it until fall, when I will participate in a robot show, and most likely, one of justin grey's robots will destroy, then burn my robot. 

rpantaleo (author)seraphus2010-06-09

Hey, I just found your instructable today; awesome! Glad you're trying to improve the design, mine was built on limited time and budget (and a bit of inexperience). I definitely cut a few corners. 

Yeah, I wonder what's up with the sleeve bearings getting eaten up. The original hexabot maybe has about 10 hours of loaded operation on it, and it hasn't had any problems with things getting really worn out. There's more slop in the joints than when it was first built, but nothing too terrible. Only thing that immediately jumps to mind is an over-constraint problem. Maybe if the tube inserts in welded into the legs and linkages have some angular misalingment, combined with the tight fit of the brass sleeve, there could be excessive wear? Or maybe the brass sleeve is just too thin? This is a puzzling problem.

r570sv (author)seraphus2010-04-29

Interesting about the motors.  Lots of people have used those in battlebots without issue (at least they look like NPC motors).  How are you controlling them? 

How much does this thing weigh?

rimar2000 (author)2009-12-03

Will continue?  I am anxious...

seraphus (author)rimar20002009-12-03

 Yeah, I spend about 3 5 hour days a week working on this specific project. I've got a little more lathe work to do, so I might get some detailed pictures and details on that process. If not, it'll skip to Relay control! 

About This Instructable

4,322views

9favorites

License:

Bio: Just your average robotics and fire arts tinkerer.
More by seraphus:Six legged walker with strong joints!Cast Tin!NiCrome "hotwire" ignition for propane flame effects
Add instructable to: