Wow 
That’s stunning! Looks really great and professional.
Can’t wait to see it finished. 
The design (fully enclosed), use of molded plastic etc. makes it look like you purchased it. What are your thoughts about production?
I would like to second the others and say WOW!
Thanks guys, I’m glad you all like it.
I’m not adverse to the idea. However, there are certainly things I would change in order to make production more efficient. Mainly mold design to make parts easier to remove and make molds last longer (mostly for deep molds like the body). These changes wouldn’t be hard to implement; I’ve learned what I needed to through my build. But, since my ‘prototype’ is also my final product they probably won’t be implemented at the moment. Unless I was to make a good amount of these, the resources to redo a lot of these parts wouldn’t be worth the investment to change minor details.
Like most things, the set up is the expensive part. Prototyping board, silicone, tooling, and time aren’t exactly cheap. However, once the molds are produced it’s 10-15 minutes of work, $0.10 to $1.50 worth of polyurethane and maybe $0.50 worth of disposables and you’ve got nicely casted parts.
Thanks CodeMaster, sorry I missed your question. It’s a small fan to move some air through the body. The voltage regs, servos and motor drivers are all enclosed in the body so I didn’t want too much heat to build up.
So I said I post more of the process. This will show making the silicone mold. Here we go:
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Grab your mold
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I use my CAD software to figure out the volume of the mold cavity, then subtract the volume of the part from that to find how much empty space needs to be filled. I do a little math to figure out how much silicone I need, by weight, and add a little extra to be sure it overflows the mold just a bit. Then I weigh out the components.
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Then mix it well and place it in the vacuum chamber to degas. The container you mix in should be at least 3 times the volume of the silicone. That allows space for the silicone to expand as the bubbles grow. After a short amount of time the silicone collapses and it’s ready to pour into the mold.
You might be able to see that my container wasn’t three times the volume of the silicone in it. In this case, I let the silicone rise to the top, release vacuum, let it rise again, release vacuum, and continue to do this until it collapses.
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Pour silicone into the mold to fill it only part way, making sure that every surface is covered by at least a little silicone. This is important for degassing a second time, allowing the silicone to get into every tiny detail. In this pic you can see the chamber extension I had to make. Just a tube with a similar diameter that I made a gasket for with silicone window sealant.
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Fill the mold with the remainder of the silicone and leave it alone for several minutes to allow any bubbles to rise to the surface. Give them a gentle blast with canned air and they’ll pop quite easily.
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Take a sheet of hdpe large enough to cover the entire block and place it on gently, starting from one side and lying it down slowly so that no air gets trapped underneath. Then put the classiest (yeah, beer bottles. That’s classy) weight you can find on top to clamp the sheet down. This will push extra silicone out and give the mold a flat bottom.
The size of the mold will dictate how much weight you’ll need. I’ve got 6lbs on this one. Just be careful not to weight the middle too much or you’ll have a depression in the middle of your mold from the sheet’s deflection.
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Next you’ll remove the mold. This involves cussing, sweating, bleeding, more cussing, sawing, wondering if it’s worth it and finally getting it removed. Ha, this was actually an isolated case, usually it’s pretty easy if the mold isn’t deeper than 7mm. This one was 23mm deep so it was very difficult. Needed more draft angles.
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Now you just cast your part. It’s pretty much the same exact process just using polyurethane. You’ll also probably need to do it faster since the curing time is usually shorter.
So that’s pretty much it. I’m sure there are details I missed so if you have questions let me know.
Thanks for posting the process - it’s very informative and helpful! 
I might have a go at some point. :mrgreen:
awesome good idea with the fan are you still going to put a turret on it like in your orignal robot design?
Yeah, I still plan on putting the turret on it. But, that will be a little way in the future. I want to get it up and walking first before having other things to worry about.
You can see where I plan on mating the turret in some of the pictures I posted earlier. There’s a circular cutout on top with some tapped holes.
Hi, Marcham,
Excellent description of the process of forming the mold from the original “positive”. I was particularly interested in the degassing procedure.
I have made several molds for casting structure walls for my G-Scale (1/2 inch equals 1 foot) garden railroad. I have not used degassing, yet. But I hasten to point out to others interested that my walls are large, flat, area rich subjects with relatively little depth involved - maybe 3/8 inch at thickest points. Thus natural degassing seems to have worked satisfactorally. But not alway perfectly. There has been the occasional surface blemish caused by a bubble. For my purposes this could be fixed in the casting by filling with modeler’s putty or grinding smooth. This would NOT be acceptable for robot parts or for other railroad parts such as rolling stock truck bogies or for figures and other details which have more relative third dimension than my walls.
So I plan to incorporate Marcham’s degassing process into my future molding projects. I’ve seen it recommended before but never as well described.
For those building their original “positive” some way other than by CNC milling with a CAD program, there is an alternate way to determine volume. You need to afix your positive into a little walled framework before pouring the liquid silicone anyway. Before mixing the silicone, pour water from a measuring cup into this frame to get the volume. Dry this thoroughly before making your mold.
Thanks again, Marcham.
Ted
Thanks, Ted!
This is a good idea. The old ‘Eureka’ method.
Assembly is coming along. I need to come up with a different solution for the photointerupters I plan on using as encoders for each track assembly so I may be delayed for a few days.
Stop doing that…
Awesome, that’s simply perfect!
Looking forward to see it in action.
thats awesome, the fan is a good idea
cant wait to see it take is first steps
AWESOME!
Perhaps I missed it and I apologize if you already covered it, but what was the rationale to have the robot walk on rods instead of the tracks themselves, or have the rod protrude only from the very end of the track unit making it much shorter? Also, which movie are you making it for? 
Any plans for military colors (mat black / dark green / mat grey / desert sand)?
It would look cool in camo
The rationale behind the rods is that, regardless of leg orientation, the point of ground contact is consistant and predictable.
Here’s an example pic of what happens to the point of ground contact through some of the range of motion of the legs. With the rod, you can tilt the leg any direction and keep the same point of contact. Without the rod, tilting the leg would cause the point of contact to change. This would change the gait dynamics. Also, trying to rotate about a point instead of an area is easier (for example, dancers spin on their toes, not with their feet planted)
As for the reasoning to why the rod is placed where it is. The track vertex nearest the foot is where the motor, gears, and encoder is. It’s already a mess down there so trying to package in the rod would have been difficult. Also, in it’s current configuration, the rod is clamped directly to the servo, making the connection much more rigid. Oh, and I think it looks cool.
And different color schemes are certainly possible. I buy one translucent base resin and just mix in dry pigments to get the color I want. I don’t think I’m going to jump into making a different one quite yet though; it took enough work to get where I am and there’s still plenty of things to do.
Wow looks really professional, as has the whole process you have presented us with.
Looks like you can buy this off the shelf.