Aluminipede, a small walking machine

Postby rodiponer » Thu Mar 11, 2010 12:04 am

Thanks Dragonfly. I just remembered that the poles in my shade structure are aluminum, so I will check them for corrosion. Though I have no idea what alloy they are. I am using 6061 and 6063, which is pretty corrosion resistant.

Since I've last checked in, I have been making a whole lot of the leg joints.
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I learned about galling. An engineer relative told me that my leg joints would eventually seize, because they have aluminum-on-aluminum action. Just like aluminum will clog up a drill bit or end mill, the two aluminum faces in my joints will rub up against each other and rub tracks then little boogers will roll up and clog it. All I have to do to prevent this is put another material in between it, so I got these little 0.001" shims. They can be very difficult to install in the joints as I am assembling them.
Image

Today I machined the first ball bearing joints. There are only two of these on each leg, and are for the joints that are under the most load. With a full load of passengers these joints will have ~200 to ~250 pounds on them.

But now that I have made a few of these ball bearing joints, I think they may not be worth it. The plastic sleeve bearings seem equally slippery with my primitive experiments (of pushing them together as hard as I can and seeing if gets more difficult to twist them). Tomorrow I am going to try and devise and experiment that will put both styles of leg joint under 250 pounds of load and see if there is an appreciable difference.
Image

I have also learned that the nylon sleeve bearings catch on fire if you weld even several inches away from them.

I am also nearly finished with the Mutant Vehicle application. I draw like a third grader, and am trying to con my wife into making at least one nice looking concept drawing to submit.

I read that mutant vehicles cannot have lights that impersonate an emergency vehicle. Is a rotating yellow light against the rules? I am planning to put a rotating yellow light underneath the machine, which would shine out from underneath the legs. This would be a "stand back" warning light, like you see on a forklift or airport people mover, for when the machine is about to start moving and there are people around.

I also like that the walking robot forklift in Alien had rotating yellow lights. But of course if this is against the rules I can figure something else out. It would be funny to have one of those backup beepers like a garbage truck.
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Postby LeChatNoir » Thu Mar 11, 2010 6:44 am

Great looking work. I like the first shot of all the parts in a pile. A beautiful thing.

As the machine actually gets up and running, keep an eye on those thin shims. They may wear through. It might be an idea to use a slightly thicker shim or even a sintered bronze thrust bearing. If the pin that these joints pivot on is also subject to galling you could press in a sintered bronze flange bearing (sold at tractor places and local hardwares) if it becomes an issue.

Email the DMV about the rotating light. Should be a link on the MV app page. I think it' be a cool look if they don't have any issues with it. Maybe a color like green could be acceptable if yellow isn't. Double plus good with a back up beeper.

On a side note, I've had good results with nylon bearings and washers holding up during the powdercoating process. This is usually around 400 degrees F and at the top of the tolerance for this material, but it seems to do ok.
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Postby motskyroonmatick » Thu Mar 11, 2010 3:14 pm

My gut reaction is that a yellow or amber rotating light should be fine. Many over the road trucks that carry wide loads use them to alert other motorists. Pilot cars, construction vehicles and even meeter readers use them. I believe it is a common and legal way to alert the public to a hazard.

Red and blue flashing strobes or rotators I am sure would be strictly forbidden as it is only legal to use those on actual emergency vehicles. Occasionally you will see blue lights on volunteer fire fighters vehicles as they respond to the station for a call but many districts have done away with this. My district won't allow it.

Go for it and don't for get to put some small head lights on the front and red tail lights on the back. Apparently this is to make it so LEO and participants can see what direction the vehicle is going at night at a glance.
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Postby theCryptofishist » Fri Mar 12, 2010 12:01 pm

motskyroonmatick wrote:My gut reaction is that a yellow or amber rotating light should be fine.

My gut reaction is to check first. I remember issues with flashing lights, and better safe than sorry. It's probably on the DMV rules.
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Postby rodiponer » Fri Mar 12, 2010 12:41 pm

theCryptofishist wrote:My gut reaction is to check first. I remember issues with flashing lights, and better safe than sorry. It's probably on the DMV rules.


Thanks, I emailed to ask about lights and two other small details.

The DMV rules do not mention yellow. I read some state laws that say Blue and Red are reserved for police, fire, and a few others. Yellow can be used by private security, construction, wide loads, tow trucks, farm equipment, cranes, garbage trucks, public utilities, and etc. But I also read that, on the playa, the DMV Interceptors use yellow beacons to keep track of each other. So it's up to them as to whether or not another rotating yellow light would be confusing. It's not important to me, just one little detail among many.
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Postby dragonfly Jafe » Fri Mar 12, 2010 5:59 pm

...a rotating UV light could be interesting though...
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Postby LeChatNoir » Fri Mar 12, 2010 9:02 pm

That's genius!
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Postby rodiponer » Sat Mar 13, 2010 10:51 am

They wrote back quickly. The yellow rotating beacon is ok for limited use as a warning signal. Which is cool, because I think it will get the point across and I'll only spin it for a few seconds when the machine starts up and there are people nearby.

They want more details and careful thought from me about pinch points on the leg. The leg mechanisms have parts that cross over each other, an sticking your hand inside the legs while the machine is moving is akin to sticking your hand in the spokes of a bicycle wheel. It won't scissor your fingers off but could easily crush or bend them the wrong way. Not a smart thing to do, but people won't have exerience with the legs and know that sticking their arm in them is as dumb as sticking their arm into a rolling wagon wheel. A friend of mine is good at technical drawing and is going to help me illustrate what the danger is for the DMV and then we can try to figure out a way to minimize the danger to whatever degree they want. I don't think they are going for the Disneyland standard of people being willfully stupid, that would be depressing. So maybe a few cover plates or something like that strategically placed will work while also not obscuring the beautiful motion of the legs too much. Or maybe we'll have to commit to having walkers by the machine when we are near people, I don't know if they would accept that. I'll ask once I have drawings.

What have you guys done with pinch points on your vehicles that was acceptable to the DMV? Does anyone have an idea of the standard they are going for-- to protect just the carelessly placed hand or the willfully stupid? Maybe that's a hard thing to quantify.
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Postby rodiponer » Sat Mar 13, 2010 11:40 am

What would a rotating uv light look like? Is it invisible except when it hits glow paint or people who use the right laundry soap?
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Postby dragonfly Jafe » Sat Mar 13, 2010 12:07 pm

rodiponer wrote:What would a rotating uv light look like? Is it invisible except when it hits glow paint or people who use the right laundry soap?


...I would imagine so...


rodiponer wrote:Or maybe we'll have to commit to having walkers by the machine when we are near people, I don't know if they would accept that.


...this is the typical solution for vehicles that are too big, have limited driver visibility, or have other dangers. Just be sure you have a good plan for communicating between walkers and driver (radios are suspect unless you have a private frequency - lots of competing radio traffic on most public freqs).
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Postby rodiponer » Mon Mar 29, 2010 10:56 am

I spent the last week making a large CAD file for the DMV application. This is the first large assembly of small parts I've made in CAD, and I had start over a few times until I learned how to organize all of the mechanical limits.

To decrease the risk of people putting their hands inside the legs as the machine is walking, I added a remote control so that the driver is now also the side walker, and then wrote a bunch of operating procedures about that in the DMV application. A relative who is an electrical engineer is going to help me make the remote control and wire it into the motor controllers. We found these cute little X-BEE wireless controller modules that will handle the wireless link without very much fuss, while also giving us error checking to slow the machine to a stop if the wireless signal becomes unreliable (using an RC airplane radio wouldn't give us that).

Here is a rendering of it without the perforated aluminum skin. To give you an idea of scale, almost every tube is 4' long (this makes assembly a lot easier):
Image
Image

Today I am making a prototype of the flat plates on my CNC mill, and will then send these out to a cutting place to make 90 of them. I've only done water jet cutting in the past, and have heard that plasma is a lot less expensive but requires some finish work to remove the slag. Do you guys have any experience with how much finish work would be necessary for plasma cuts 1/8" aluminum plates? I am making the holes for the 1" tube about 1.03", so I don't mind a little bit of filing to remove slag if it comes off easily, or if it breaks right off if I ram the tube into the hole, but with these tight tolerances it would be annoying if the slag is very sticky and I have to grind or file every tiny little speck.

The drawing gave me an idea for lighting the machine. The edges of the cube are made of four 1" tubes that are held 2" apart by plates of aluminum. This is to make the chassis very strong without a lot of weight. I want to keep the weight very low so that the mechanical details (motors, drive train, batteries, axles, hinges, whatever) are easy to way over build. I am thinking of twisting RGB flexible strip lighting into a plastic tube that fits between the groups of four 1" tubes. So there would be one of these tube lights on each edge of the cube. Maybe I can find frosted plastic tubes to diffuse the light from the LEDs, or maybe we could stuff silk or nylon or tissue into the tubes to diffuse the LEDs. Or do you guys have any better ideas for lighting these edges?
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Postby Ugly Dougly » Mon Mar 29, 2010 10:59 am

Can't have enough walking machines on the playa. All respect! :)
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slag

Postby motskyroonmatick » Mon Mar 29, 2010 1:17 pm

Slag from Plasma Cutting should be minimal. I imagine it would only take one fast pass with a grinding wheel to remove any cutting contour and slag that may exist. You may also want to try a flap sanding wheel or a grinding style wheel that has sand paper glued to it(sanding disk?). Both the flap wheel and sanding disk will be less aggressive and would leave a smother looking finished product if that is a concern. Sharp inside angles or corners will be impossible with a flap wheel.
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Postby LeChatNoir » Mon Mar 29, 2010 11:08 pm

Slag can depend a lot on operator skills. Steel slag knocks off (95%) with a hammer and a flap disc cleans up the rest. I’ve found aluminum slag to be stickier, but still come off easily enough with the same type of flap disc. We use 60 grit in the shop exclusively. Nice balance between aggressive removal and smooth finish. Go up or down depending on what you need out of it.
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Postby moltensteelman » Tue Mar 30, 2010 4:46 am

I would recomend lexan panels on the sides of the passenger compartment to keep peoples hands and feet out of the linkage, as well as a few ground walkers. I look foreward to seeing your creation on the playa.
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Postby moltensteelman » Tue Mar 30, 2010 5:26 pm

I wouldn't worry too much about the aluminum corrosion, 6061 and 6063 have good resistance. I have been building and sailing land yatchts on the playa for 13 years with no corrosion problems. A light rinsing with a hose or compressed air after each trip seems to work well. Aluminum will turn grey after the first year or two and will stain if playa and water sit on it too long. If playa gets trapped inbetween panels or in crevises it may cause some corrosion. If you decide to paint the aluminum use an acid etch primer or the paint can flake off.
I'd recommend adding a little more clearence between the legs, parts tend to flex while cornering. I have 1 1/2" clearance on the Walking Beast and the legs sometimes rub against each other.
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Postby LeChatNoir » Tue Mar 30, 2010 6:37 pm

Now, that is some good, firsthand playa-tested knowledge, moltensteelman.
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Postby rodiponer » Tue Mar 30, 2010 11:00 pm

Moltensteelman, your machine is so awesome. Thank you for your thoughts here.

I'm planning to use perforated aluminum on the side walls, with 1/4" staggered holes so it should be easy to see through. These are the largest holes that my daughter cannot slip her fingers into. Lexan would be better but I'd feel compelled to keep wiping the dust off of it.

Thanks for the tip about legs flexing. The dynamic loads are really the big unknown for me, since I don't have the engineering background or fancy CAD software to figure it out-- so I've just been way over doing the static loading. I've seen videos where the Walking Beast chassis twists after each step and have been keeping that in mind. My legs are drawn with a 1" clearance, but I can increase that if they need more. I'll assemble that part of the chassis first and see how much the legs can flex before I weld it together.

I'm glad 6x aluminum has worked well on the playa.
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Postby moltensteelman » Thu Apr 01, 2010 7:06 pm

Thanks, The perforated aluminum is a good idea, it should let some air through without the greenhouse effect like polycarbonate. Polycarbonate also creates a lot of static electricity and attracts dust. Keep in mind that initial flexing will be a less than when the machine is broken in and parts start to wear a little. Yes, the Beast has a bit of sway, the legs are supported on 8 foot long main arms. The arms are connected to additional pivot arms at one end and in the middle so a little movement at one end translates to a lot at the other. Also mass really increases flex, I'm at 13,000 lbs. before I add 6 or 7 people. I think with the size of your machine you should be alright but additional clearance is always one less headache later on.
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Postby illy dilly » Fri Apr 02, 2010 2:11 pm

How did you get your CAD files to load?
Did you just .pdf and/or .jpg some layouts or print windows and load them on a website?
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Postby rodiponer » Fri Apr 02, 2010 2:52 pm

The CAD software I am using has an "Export to JPG" option, which is the same as saving a screenshot. I then uploaded it to a server and used an img tag in this forum to put it in the message.
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Postby illy dilly » Fri Apr 02, 2010 3:28 pm

That's kinda what I figured. I'll just load them up on flikr. Thanks for your help.
What CAD are you using?
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Postby rodiponer » Fri Apr 02, 2010 4:04 pm

Alibre Standard. Before this I used Sketchup, but I needed true curves and circles for the CNC machining. And now I really like the parametric workflow.
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Postby rodiponer » Fri Apr 16, 2010 10:13 pm

Today I picked up 72 48" 1x1x 1/16" aluminum tubes to make the chassis.

The 132 water jet cut parts should be ready early next week. Between now and then I have to drill 308 holes into the tubing for the rivets that will fasten the tubes to the water jet parts. LeChatNoir had the great idea of using the CNC mill to do this, so that I only have to load the tube into the vice two times to drill four holes. This is more accurate and faster than using a drill press.

Image
Image

I am glad I am riveting this machine and using flat plates to join the tubes. I've been practicing TIG welding for an hour a day, and have learned that my welds in 1/16th tubing are not strong at all. Or maybe 1/16th tubing just isn't very strong to begin with. I can easily break any weld I make in this tubing by slipping a 4' pipe over it and pushing a little. The welds seem to just rip apart like cardboard. With 1/8th thick tubing I can't break the welds with a 4' pipe.

So next week I will be drilling and riveting. And a little welding to make sure the water jet cut plates don't slide along the tubes. The idea behind this weird construction method is lightweight strength. The tubes are held apart and made into 4" square beams that weigh about the same as 2" square tubing but is much stronger. I'll see how it works out, or if it is even necessary to go this high tech.

I need to get better at out of position welding. It was easy with MIG, but with TIG I can only weld when something is horizontal. When I am welding vertical with TIG the torch is a lot more jittery in my hand and I tend to dip the tungsten into the puddle. Or keep jittering my hand slightly, so the arc is wandering around quite a bit and heating up the whole piece instead of making a nice little puddle, so I sometimes burn a hole through the piece from too much heat. I think resting my hand on the work, when welding horizontal, is a bigger crutch for me than I imagined. A painter or calligrapher would have a big advantage here, in having a practiced steady hand. I don't think I'll be able to flip the chassis around so that whatever I am welding is always face up, so I have to get better at this. Maybe I need a big clamp to move around and rest my hand on as I go.

Corner welds are still a problem. I am getting better, but my corner welds are still really bad. The root of the corner is completely cold, so the bead is just sticking on the sides, about 1/16th to 1/8th of an inch away from the corner. If I cut a practice weld with a bandsaw I can see that the bead is not fused to the corner at all and just sitting on top of it, like you'd see a crease inside playdough that's been folded, while it looks well fused a little distance away. By accident I found a technique that is probably bad-- if there's a slight gap in the corner I can melt the two pieces above and below the corner and then stick the filler rod into the gap, to let the surface tension make a new corner that is fused to both pieces of metal. But that's not really a solution. From all of this practice my bottle of argon is almost spent, so I am thinking of trying a helium-argon mix next: I've read that the arc is more focused when there is a little bit of helium in the gas, so maybe that will let me poke the arc into the corner rather than having a wide cone that seems to want to go everywhere except the corner.

Sometimes my weld beads have pin holes, some kind of ugly nub, or a ball where the bead didn't flow onto the base metal and just rolled onto it with that water-on-wax surface tension-- is it bad to run the torch back over a bead to reliquify these defects or the base metal to smooth these things out? I still don't have the 'stack of dimes' look on anything except a piece of flat plate.
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Postby Sail Man » Sat Apr 17, 2010 9:02 am

Ummm, you are making enough of these for everybody in Kidsville, right? :wink:


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Postby masho » Tue Apr 20, 2010 9:52 pm

sweet project, nice rendering, great thread. Thanks for taking the time to walk us through your trials and tribulations. :wink:
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Postby motskyroonmatick » Wed Apr 21, 2010 12:15 am

My problems with wandering or wide arc off of the tungsten usually come from a contaminated tungsten. My welds always look best and are created the easiest with a fresh tip on the tungsten.

That is all I can think of to help out.
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Postby rodiponer » Thu Apr 29, 2010 9:34 pm

The chassis plates are now cut.

Image
Image

The holes in the plates are for solid rivets to bam through the tubes. Rather than pre-drilling the holes in the tubing and hoping that everything lines up perfectly, I am thinking of using the holes in the plates as guides to drill through the tubing.

Is there some kind of tool that makes it easy to drill at a right angle to a surface, like a small drill press that clamps onto the thing you are drilling into? Or a collar that's like a router and has a depth lever or something? Or is a flat assembly and the little bubble level on the top of the drill really the best way to make sure you are straight?

My hour a day of TIG welding practice has been going very well. I took a break from aluminum and started welding scraps of steel for a little while. It's so easy by comparison-- I was able to get beautiful corner welds on thin steel sheet. I think being able to practice welding at the slow pace of steel helped me figure out exactly what I should be doing with aluminum at a much faster pace.

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Postby LeChatNoir » Fri May 14, 2010 6:12 pm

Ok, man… it’s been a while. What’s the news? Give, give...
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Postby LeChatNoir » Fri May 14, 2010 6:23 pm

rodiponer wrote:Is there some kind of tool that makes it easy to drill at a right angle to a surface, like a small drill press that clamps onto the thing you are drilling into? Or a collar that's like a router and has a depth lever or something


It may be too late now, but...

You can make a drill block by drilling a hole with your selected size of drill on the drill press through a chunk of steel an inch or so thick. By placing this block over your center punched location, you can keep it roughly square. Probably square enough at least. They make drill bushings that you can insert into a block to serve the same purpose in a long term situation, but a simple hole will work for short term.

I've seen some drill-press type things that you use a cordless drill with, but have never been impressed enough to buy another one after the one I had broke. Might work for this situation, though. Check Harbor Freight.
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