Mëtal Scooter construction update

A lot of work and progress has happened since the last Mëtal Scooter status update. Starting from the beginning:

A brand new Razor scooter about to be destroyed for parts

The McMaster-Carr, HobbyKing, Amazon, and Ebay shipments all arrived roughly on time. The first order of business after checking all the items was to remove the handle and steering mechanism from the Razor scooter. The wheels, deck, brake, and other miscellaneous pieces weren't needed. By using the Razor mechanism on my scooter, i'll not only save money but also get to take advantage of the folding feature of the handle. I did notice that the new Razor A2 design seems to have a 1-2" shorter handle (at maximum extension) than the one I had as a kid. In order to raise it to a slightly more comfortable height, I intend to add about a half inch of aluminum spacers at the bottom when I attach it to my deck. Feeling bad about just tossing the unused parts though, I decided to just try installing the front wheel directly into the deck:

This really didn't work for obvious reasons

Next I moved on to a task that I was really excited about: cutting 5052 .25" aluminum plate on the ShapeOko CNC. I had also received some proper 1/8" carbide milling bits with the Amazon order, so everything I needed was ready. Beginning with the scooter's deck risers, I started to experiment with different variables in the CAM software. At the start, about half of the cutting attempts were successful. I lowered the pass depths to about .005"  at a medium feedrate. This was more successful, but a problem with metal shards landing on the Y-axis rails created very jerky motion that ruined a few more attempts.

A successful piece

As a quick fix, I stuck some duct tape to the interior vertical sides of the rails to block most of the aluminum chips. This worked pretty well, but regular cleaning after every two pieces was necessary. The biggest improvement came with the use of a cooling/lubricating fluid (instead of the water I had been temporarily been using that the beginning). While I still haven't gotten around to purchasing some real machining fluid, the bottle of air tool oil that I found on a shelf has been doing a remarkably good job of improving the ShapeOko's aluminum cutting ability. As a bonus, it is also heavy enough to block most of the metal chips that come off the the cutter. I realize that this is probably a far from ideal fluid, but I don't really feel like spending money on the real stuff until it runs out. After this point, I could finally begin cutting pieces with more efficiency:

The bottom right riser has some visible damage from when the cut part got suck against the bit

Each piece was drilled through on the side for connection to the aluminum U-beam that acts as the scooter body. Due to a couple stupid moves on my part, two risers had to be shifted to the side after I broke off a tap in the original holes. Overall though, I think that this process ended up pretty close to the design:

Before moving on to the deck, I decided to cut the slot for the back wheel. It was pretty quick and easy using a table and band saw. The cut is still a little rough, but I might give it some filing when everything else is done:

The wheel on the back is not the one specified in the original design. Instead of pneumatic wheels that would provide some shock absorption, I opted for hard rubber wheels because I had them laying around and they were free. This might will definitely need to be changed at a later time if I decide to use this scooter regularly. While I may have cheaped out in every other aspect of this project, I did pursue the carbon fiber deck. Having done a little bit of work with carbon fiber before, this time I decided to lay out a proper area to assemble and cure the deck:

The wax paper in the center is what the carbon fiber will cure on 

I don't have any pictures of the process because my hands were in epoxy covered gloves, but it was pretty simple. I chose to use unidirectional carbon fiber from a local Tap Plastics because it was convenient and much more reasonably priced than the standard weaves. I put down four layers total (wetting each with epoxy as I went). The bottom and top ran lengthwise for looks, the 2 sandwiched layers in between ran perpendicular. When I was done, I put down a final sheet of wax paper and lowered a heavy piece of oak lumber to compress it. After 8 hours of curing (I couldn't wait overnight) I peeled off the wax paper to get a look:

The notch was cut later on a bandsaw

Overall, it was disappointingly wrinkled on the surface. Despite efforts to keep everything smooth, one side turned out badly, and one turned out OK. The OK side became the top surface. While the wrinkles didn't ruin anything (or compromise its strength), it meant that I ultimately had go through the sand down+reapply epoxy process four times to get a good finish. Four layers seems to be about the minimum thickness that is safe to use as a standing platform. There is some flexing from the deck that will hopefully be eliminated after screwing it down to the risers. On the positive side, it is extremely thin and looks kinda cool up on the risers (in my opinion).

Next I turned to the drive system. To connect the motor to the body, I needed to make a very large and unusually shaped motor mount plate:

The shape is so bizarre because it has mount in-between the back wheel and the end of the rear slot. After it rises above the deck level, it widens to fit the motor. The slots should allow the motor to slide when the bolts are un-tightened. Because the chain won't have a real tensioner, i'll just slide back the motor to take up slack. The motor mount will also need some aluminum spacers to line up the motor and wheel sprockets. This part presented a good challenge for the ShapeOko. When cutting it, I choose very conservative settings and used lots of fluid. It took about 4-5 hours at this snail pace, but the final results were great:

Also pictured are the two pseudo rectangular aluminum spacer pieces for the motor mount, and the scooter front cover/headlights. The headlights were just an idea I had for fun. I had ordered four superbright white LEDs from All Electronics a couple months ago, and I soldered them to a perf board with a resistor to run on 5 volts. The aluminum front fits into the U-beam like this:

And the LEDs do what they are expected to do too:

Much brighter in real life than the picture appears

Getting back to the drive system, I spent a couple hours working on an unorthodox method for connecting a sprocket to the rubber wheel:

Those are 5 carefully positioned and adjusted threaded rods tapped into both the wheel and the sprocket to hold it an exact distance away from the hub. It was a long process to get the sprocket completely parallel to the wheel with minimum wobble. Unfortunately, I later realized that it was impossible for me to connect the smaller matched sprocket to the motor I had purchased. These #25 sprockets and chain had come from a junked electric scooter a couple years before. That scooter used a brushed motor with a strange shaft to hold the sprocket on. Despite another couple hours of attempts to attach the sprocket to my standard-shafted motor, I ultimately couldn't find a way to securely connect it. I've finally decided to just purchase some standard #35 chain and sprockets from McMaster-Carr. The parts should be arriving later this week.

The last element of Mëtal Scooter that I have worked on is engraving the deck. Realizing that cutting letters through the carbon would probably weaken it even more, I decided to try to use the mill to engrave into the epoxy. This was a pretty scary process. I ran the code on at least two test pieces and double checked all the settings and machine parts to make sure that everything was perfect. To get the deck into the ShapeOko's 8x8" milling area, I slid it under the Y-axis rails and then screwed it down directly to the worktable through the pre-drilled riser screw holes. The deck is one of the few pieces that I can't easily replace without a lot of work. There would also be no way to hide any mistakes if I messed anything up. It took five false starts to get the zero level right on the Z-axis (the surface wasn't completely level), but it finally got set correctly:

The improved epoxy finish is more visible here. The engraving went very well, and I really like the depth of the letters. The epoxy dust that is making the words visible in the pictures will soon go away, so I think that I may brush in a metal paint on the engraving. One final coat of epoxy over that should make it durable and still slightly indented.

Construction is moving faster at this point, so I will probably post another update soon with more about the electronics and drive system. I'm also planning on adding a lot more information to the ShapeOko page, especially more details about the aluminum cutting and future modifications.