In the spirit of The Contraption thread, or the Playa-Piano, I am creating this thread to ask anyone with interest in my vehicle for advice and thoughts on details while constructing it.
I am building a twelve legged walking machine. If I am lucky it will work. And if I am even luckier I will finish it in time for Burning Man this year.
The machine uses the Theo Jansen 'Wind Beast' style of legs, which have an entirely different gait from the Walking Beast: http://www.moltensteelman.mechanicalspider.com/
The Theo Jansen style of leg does not require the drive system to lift the weight of the machine, so small electric motors can be used instead of a large engine.
Here is an example of the legs I am using:
This will be a small vehicle, 6' long, 8' wide, and 6' tall, constructed of aluminum tubing and sheets, and it should weigh less than 300 pounds. The legs will be four feet tall and each one will be four inches wide. The passenger compartment will be about 4' by 4' and 4' tall, with pillows or bean bags to sit on.
I have been working on this vehicle since October and, in the process, have learned basic machine shop work, CAD, and a whole lot about mechanical engineering. I am currently machining a couple hundred joints for the legs and drive system, and have enough parts to make the first couple legs.
I just traded my MIG welder for a TIG welder, and have about three days of practice TIG welding. I have figured out how to reliably weld thin aluminum tubing. But welding the clevis joints to the thin walled tubing is much more difficult. The clevis joints are a larger solid piece of aluminum that heats up much more slowly than the thin tubing, and so it's hard to get both pieces heated up to the right temperature at exactly the right time without blowing a hole in the tubing. I have solicited help on specialist welding forums, and know how an expert would do this, but it may just be beyond my skill level with the TIG at this point.
I am thinking I may have to fall back on mechanically fastening the clevis joints into the tubing. Each joint should see, at a maximum, about 100 pounds of compression, so even very small rivets are strong enough.
Do you guys have any advice on solid rivets (not pop rivets)? I like rivets more than bolts because they have a more finished look and will sit more flush with the surface than bolts. The legs will only have one inch of clearance between them, so it's better to not have bolts protruding from their sides.
From my Internet reading, it looks like there are four ways of attaching solid rivets:
- Bamming with a hammer (free, or $80 tool for the special rounded punch if I do not use flat rivets)
- Bamming with a pneumatic riveter hammer ($100 tool)
- Squeezing with a river squeezer hand tool ($150 tool, if I can find one that will squeeze a 1.25" long rivet)
- Squeezing with a pneumatic squeezer ($500 tool)
I have to fasten about 200 of these joints to the tubing. These would be aluminum rivets that are 3/16 or 1/4 in diameter, depending on what I can find with a 1" finished length (1.25 to 1.375" starting length).
I've never bammed a solid rivet before. Does anyone have any advice or experience on this? How hard is it to bam an aluminum rivet? Is it nuts to try and do a couple hundred with a hammer and punch thing-- is the pneumatic hammer really the way to go? Is the pneumatic hammer frigging loud? Is the cheap one Harbor Freight sells good enough-- I mean, all it has to do is bam, right?
Here is a photo of the leg joints I am making, with the bottom side slipped into the tubing. On the right is another failed welding attempt.