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Bits to Atoms: Building the Millenbaugh Motivator, Part 3

By Sean Charlesworth

Progress on the Millenbaugh Motivator marches on! All the measurements have been made and a rough version has been modeled and approved by Adam. This week we take a look at modeling the final version and speccing hardware.

Progress on the Millenbaugh Motivator marches on! All the measurements have been made and a rough version has been modeled and approved by Adam. This week we take a look at modeling the final version and speccing hardware.

I decided to tackle the ‘valve arms’ first since I wasn’t sure how to build them. They look relatively simple but on closer inspection there’s multiple compound curves, plus the forked portion at the back and I couldn’t easily build them using my regular techniques. I ended up drawing them as 2D splines (curve described by interpreting points) on top of the reference photo--if you are comfortable using the pen tool in Illustrator or Photoshop, this is the same idea. I was able to give the spline thickness by extruding it and then used planes and simple shapes to cut out the rear fork and the front slope.

The many steps to build an arm. (click to animate)

Early on, it was tough picturing the size of some of the parts. When you’re constantly looking at blown up pictures for reference and working in 3D where things are floating in space, you start to picture things much bigger than they really are. Adam mentions this in our video when he was convinced the motivator was too small until he actually placed it on the glove. I did a test print on my MakerBot and it looked way too small, so I printed a 1:1 reference picture to easily compare parts and they were right on. I was even able to print the pivot and if a part was printable on the MakerBot (even if it was a little rough) it should print on the high-end printer without any problems.

Reference printed 1:1 - looking good!

Initially, Adam told me he would spec out all the actual hardware--screws, nuts, bearings, etc., but after the first test print I realized it would be easier for me to do it. I needed to know the exact fastener sizes in order to build the parts around them. Using the Photoshop measurements I picked an approximate fastener size and confirmed it using the free CAD files that McMaster-Carr supplies. I was also able to use the CAD files to import 3D models of all the hardware into Cinema 4D which made things much easier.

Free 2D & 3D files from McMaster made life easier! CREDIT: McMaster-Carr
Adam's excellent reference for the drivetrain. CREDIT: Adam Savage

Adam was still supplying the drive mechanism for the Motivator and sent me great reference pictures of the motor, chain and bearings. I used that info to build a stand-in for the motor so I could print it out and test it with the motor mount. I used the same spline technique to build the main blocks and top plates and was able to include all the holes needed for the hardware. That gave me the basic shape for the blocks, but the valve hollows and all the details underneath needed to be cut out separately, which required many steps. If I needed to modify something I would often have to go back to the base version, tweak it and then do all the steps to cut everything out again.

Two blocks were built and subtracted from each other to make the underside of the block. (Click to animate!)

Adam reminded me to not forget the LED lights and I was like, ‘what lights?’ since I had not seen any on the reference pictures. Adam said there was an LED underneath each valve so I had to shuffle things around a bit to accommodate those. Later, when Adam sent me a video he shot of the motivator running, there was indeed an LED under one of the valves, but the rest were dark. I heard him comment to the operator that the LED looked cool. The operator said it was just the operating light from the speed control and I think Adam liked the look and made a nice modification.

Demo video at Spectral Motion showing the firing order and the elusive LED. CREDIT: Adam Savage

Adam had an epiphany--he realized that the valve dome looked just like the end of a cigar tube.

Things were progressing well--I was up to version 3 of the main block--and Adam had an epiphany. He realized that the valve dome looked just like the end of a cigar tube so why not use those instead! I was game, so my wife and I spent a Saturday afternoon going to eight different NYC cigar shops in search of the perfect cigar tube. Explaining that I needed their crappiest cigar that came in a metal tube about ‘this big’-- and then pulling out a pair of calipers was fun.

Cigar tube in place and looking good.

We finally found a suitable tube for the large dome but they ran $12 each and since we were building three motivators that was $150 worth of cigar tubes, not counting the small domes! Thanks to the research skills of Mrs. Charlesworth, we learned a lot about cigar sizes, types of cigars and cigar cases (thanks Reddit!) and ultimately discovered that cigar tubes don’t come in the size needed for the small domes. Adam still wanted to forge ahead, he figured the large tubes would save him some work and he would lathe the small ones. I was able to track down a 30 count box of the right cigars for much cheaper online and Adam sent them my way. And since neither Adam nor I smoke and he just wanted the tubes, my father-in-law became the very happy owner of a bunch of tubeless cigars.

My father-in-law was a happy man.

Eventually, Adam sent me the actual motor, drive chain and bearings so I could do a test assembly before the final prints. The real motor differed slightly from my stand-in, so further modifications were needed--it was a really tight fit, but I was able to squeeze it in along with an adjustable motor mount. Everything was lining up and I finally had to build what I had been dreading--the crankshaft.

Notice the end cap added to curve arm. CREDIT: Adam Savage

To design the crankshaft, I needed to figure out the firing order of the valves and used the same video that the LEDs showed up in. Going frame-by-frame, I figured out the correct order and started laying out the crankshaft. I posed each valve in it’s firing order, created an offset (crank pin) for one valve and copied it for all the others, adjusting the rotation as needed. The clearances were so tight that I often had problems with the back of the arms hitting the block or the crank pin popping out of the arm. You could see from the reference photos that they had similar problems on the original. The curved arm is a great example as you can see they soldered a cap on the end because the crank pin was popping out.

Crankshaft laid out and ready to go--or is it?
First version of crankshaft hits the pivots! Back to the drawing board.

I thought I was finished and tested the crankshaft by rotating it within the program only to discover that it rammed right into the arm pivots on the right side block. Oh boy. There’s only so many measurements you can get from the reference pictures and I assumed that the crankshaft was centered on the seam between the two blocks - it wasn’t. I needed to move the whole thing back toward the left which set off a week of revisions. In order to move the crankshaft, I had to move the crankshaft mounts, which required changes to the blocks, which messed up the alignment of other hardware that had to be tweaked - it was a nightmare. This is a good example where CAD modeling may be the better choice since it’s meant for mechanical modeling and even simulating mechanisms.

I finally got the crankshaft laid out, but it needed a final test print before dropping the big bucks on the fancy printer. Up until this point, the MakerBot had managed to print everything but the crankshaft was just too small, spindly and precise to print properly. I tried every trick in the book including printing with support material.

I also have a dual head machine so I can print ABS plastic on one extruder and HIPS support material on the other. HIPS plastic can be dissolved in limonene--a citrus based product--which won’t affect the ABS. The ABS model is encased in the HIPS support, making for a much better print. Alas, even this didn’t work, the crankshaft needed too much precision, was too delicate and didn’t turn out well.

Nope. Did not work. Too rough and brittle, and broke.
Signed & Dated

Crankshaft problems aside, I was able to print the rest of the Motivator and assemble it successfully. All the hardware worked, the motor fit and could be adjusted, and there was enough room for electronics. Adam told me to make sure to sign it in some way. In the movie, Rasputin used the Mecha-Hand to release Hellboy in 1944, so I figured that Charlesworth Dynamics finished the motivator a few years prior in 1942. Having finished a complete prototype, Charlesworth Dynamics shipped it off to Adam for approval. After a test-fit on the Mecha-Hand, Adam gave the go ahead, so we were all set for the final print!

Everything done and ready to test print.
Successful test prints on the MakerBot.
The whole line of prototypes.

Tune in next week for the final print, assembly and the Motivator tested under full power!

All photos courtesy Sean Charlesworth unless otherwise indicated.