I go to a pretty geeky engineering college (Harvey Mudd) where most people use some type of wheeled transportation, ranging from longboards and unicycles, to scooters and free lines. The geeky part is many people build their own versions, customize them with engravings and stencils, and occasionally add LEDs, accelerometers, and other cool electronics.
When I visited the campus in my senior year in high school, I saw a guy who made his own longboard out of aluminum and clear acrylic, with custom machined trucks and all. For the next week I was obsessed with making my own once I came to Mudd, but then I realized I'd have to learn how to longboard, which proved to be more of a problem then I originally guessed. So, I abandoned that idea and decided to apply the same basic design motif to a scooter, cause even I can ride a scooter (I think, at least). Also, as far as I know, no one has made their own scooter here at Mudd, so it's a little more original too.
To provide a timeline: I spend the first month of school designing the scooter, and soon after ordered all the metal and some of the fasteners and other odds and ends. I began working as soon as I got access to the school's machine shop, which was around the end of September 2012. For several months I worked all day every Sunday, and completed everything up to Step 5 (the front wheel bracket). I took a break to make Christmas presents for my family like cooking spoons and decade boxes, and resumed work after Christmas break in late January 2013. I then built most of the rest of the scooter before March, and took several parts home to weld over Spring break. I laser cut the deck and finished the rest of the details near the end of the school year in April and May 2013.
Step 1: Design
Before I do any real modeling, first I do rough sketches for most of my projects, this one included. I use these to figure out the basic dimensions I need. Once I had an idea of what I was actually going to be making, I went around my college campus with a notebook and tape-measure and took measurements off of all the scooter styles I liked. I ended up choosing the Razor A5-Lux to base my scooter on. I also decided early on that I wanted to make this out of aluminum, with a laser-cut acrylic deck, and possibly LEDs for night cruising.
After 20 minutes of taking measurements off of someone's A5-Lux, I had all the dimensions I needed to do another round of sketches. Then I moved to Google SketchUp and made a full 3D model. Even though the nitty-gritty construction details were not 100% accurate in the SketchUp model, I used the model to figure out the different stock aluminum I needed, and specific cut lengths for some pieces.
Later on in the build (about 5 months later) I learned SolidWorks in an engineering class. By this time in the build, I had most of the pieces made, so making an accurate model was much easier this time around. I used this model to figure out the exact length and placement of the "folding support bar", but I'll get into that later. However, I'll open each step from now on with a picture of the part from the Solid Works model.
Once I had my SketchUp model, I made a materials list and ordered all of the aluminum from Online Metals. I also took time to figure out generic screw sizes, and ordered these from McMaster-Carr.com. I used mostly 8-32 socket-head and 8-32 button-head, with several 5-40 button-head screws for the little things.
I was originally going to purchase the replacement 8 inch A5-Lux wheels from the Razor store, however, I decided against it after I found out they were back ordered and 60 dollars. After much online research, I found that large wheel-chair casters are cheap, durable, and pretty available. I got two 8 inch wheels from some guy on eBay for less then 20 dollars.
Early on I decided I wanted the deck to be clear acrylic, so I also ordered a piece of 1/4 clear-green acrylic from E-Street Plastics. I'll use my school's laser cutter to cut out the deck. Laser cutting acrylic is great because it likes to crack and chip when you machine / cut it with regular saws, and the laser cutting also 'flame polishes' the edge when it cuts it, so it's just an all-around great way to cut acrylic!
Step 2: The Deck Support
I began by making the deck support, and worked off from that with subsequent pieces. The deck support is the part that supports the acrylic deck, the very base of the scooter.
I used two lengths of 1" x 1/2" x 20 5/8" 6061 aluminum as the 'rails', and connected them with two 2" pieces of the same stock to make up the deck support. I used a bandsaw to cut them roughly to length, and then faced the ends to length on a mill with a ~1" end mill (I did this for both the rails and connector sections). Each joint has two black-oxide 1" 8-32 socket-head screws, counter bored so the heads are flush.
For now, I just drilled one 17/64" hole (slightly over 1/4") in the front of the rails to attach the steering column uprights. I'll figure out the rear wheel mounting later.
Step 3: The Uprights and Steering Column Sleeve
Next I made the uprights, the pieces that extend from the pivot on the deck support up to the steering column. This will be the part that folds over onto the deck when you collapse the scooter.
I made this part from slightly different stock, I used 1 1/4" x 1/2" instead of the 1" (Im not really sure why I did this actually, Im writing this about 6 months after I ordered the aluminum, so who knows what I was thinking then. Im sure I had a good reason though...)
Anyways, I cut two pieces to about 16 inches, and faced one side of each. The other side had to be milled at a weird angle, so I left one side rough for now.
I also cut two 1" connector sections and faced both sides to length.
Now came the tricky part: machining that weird angle. This would have been easy if the shop supervisor would have let me swap the mill vise for a turntable, but he didn't, so I had to get creative. I ended up using regular t-slot tie-downs to clamp the pieces down to the mill bed, and then jerry-rigged a very sketchy system to make sure the pieces were lined up at 32.3 degrees to the z-axis of the mill. I had an angle measurer, but because of some physical constraint, I had to use it in tandem with two squares to make sure everything was lined up. And I had to do it twice, once for each piece.
Once it was lined up, I faced the other end of the piece to length with the angle, and then did a 1" wide 1/4" rabbit.
Thankfully, both parts came out okay!
Next, I attached the two pieces together with the connector pieces. For these joints I used 1" stainless 8-32 button head screws, and counter bored the heads with a .33" end mill. To finish off the part, I drilled a matching 17/64" hole in the end to connect it to the deck support.
The next part was even trickier. I had to mill corresponding 1/8" deep cuts into the steering column sleeve (the thing the steering column spins through). Again, I had to clamp the piece directly to the mill bed, which proved to be harder than before because it was a tube. This also made it hard to line the angle up correctly, because I didn't have a clear edge to sight down since it was rounded. After much finagling, I made the cuts and the joint turned out okay. You can see how the parts fit together in the pictures above.
Step 4: The Steering Column
This was definitely the coolest part of the scooter to make. The steering column has to spin smoothly even under a lot of pressure, and aluminum rubbing against aluminum is not good, so I had to figure out how to insulate all the aluminum in the rotating joint.
I used lubricated brass bearings which fit around the steering column and slid inside the steering column sleeve to keep the column separated from the sleeve, and a brass washer in-between the top of the sleeve and the shaft collar kept the top of the joint insulated. The bottom joint has to bear a lot of weight, so I splurged and bought a trust bearing to lubricate the steering motion.
The steering column itself I made out of two telescoping tubes. The lower, bigger one is about 1 1/4" outside diameter, and the inside one is 1" OD. I mounted a threaded plate on the inside of the inner tube, and drilled a corresponding hole in the outer tube. These holes line up at the desired hight and a threaded knob keeps them together. In the future, I may mill a slot in the outer tube so you can easily adjust the height, but for now Im leaving it at a set height.
I used a 1" end mill to make a rounded cut in the top of the inner tube so another 1" tube could fit across the top to make the handle bars. I made a plug out of 3/4" solid rod and fit that inside the top of the inner tube, the handlebars thread into this plug.
Step 5: Front Wheel Bracket
I made the front wheel bracket out of 2" x 1/4" stock aluminum, with two connector pieces made of 2" x 1/2" stock. I spaced the connectors 1 inch apart, and connected them to the side pieces with the same 8-32 screws. After I drilled and tapped all the holes, I used a CNC mill to cut a 1.25" hole in the top connector piece, and a 1.25" depression in the bottom piece. This way, the steering column can slide through the top piece and recess into the bottom one. This allows for easy welding alignment and will provide extra rigidity. Unfortunately, my college shop doesn't have a great welding set up, and we can't weld aluminum at all. So, I had to take several pieces home over Spring Break so I could weld them. I'll talk more about welding in step 9
I drilled a 0.316 hole to fit the 5/16" axel, and then I made groves on the axel to fit the retaining rings which keep the axel in place.
Step 6: Rear Wheel Bracket
This might have been the simplest piece to make. I used 1/4" x 1 1/4" stock connected by a little 1/2" x 1 1/4" piece, and attached them with four 8-32 button-head screws. I left the other ends rough because I wasn't sure exactly where to mount the bracket at this stage in the build.
I've also included a progress pic taken when I finished the rear wheel bracket. This was taken in mid February 2013
Step 7: The Folding Mechanism
For the folding mechanism, I wanted a bar to pin between the uprights and the deck support, creating a triangle around the main joint and preventing it from folding. I also wanted to be able to pull the bottom pin, fold the scooter over, and then pin the same bar back near the rear wheel to keep it folded. Accomplishing one of these would be easy, but accomplishing both is difficult, because I needed to satisfy the angle and lengths of both triangles. This problem was complex enough that I knew I would screw up if I tried to just make it, so I decided to remake the whole scooter in Solid Works so I could really get the dimensions for this part right.
Since I already had most of the scooter built, making it in Solid Works only took several hours because I already had all the dimensions and details figured out.
Once I got the scooter model built, it took about an hour of tweaking the length of the folding bar and placement of the holes before the scooter locked in the unfolded position at the right angle, and locked in the folded position so the steering column was parallel with the deck. I took dimensions off of the model and used these to make the real part.
Step 8: Welding
Like I said earlier, I didn't have the facilities to weld aluminum in my college shop, so I had to bring several pieces home over Spring Break so I could weld them.
When designing, I tried to limit the welding as much as possible exactly for this reason, but there were still several joints that just couldn't be made with screws. These are the joint between the uprights and the steering-sleeve, the steering column and the front wheel bracket, and the ends on the folding bar.
I dont have a TIG welder at home either, but I read online that you can actually weld aluminum with a MIG setup if you use a special aluminum filler wire instead of the regular steel stuff, and use 100% argon as your shielding gas. We also had to replace our gun-tube liner, diffuser, and tip, because I guess you can't use any parts that have touched steel welding wire. Something happens at the chemical level that screws up aluminum welding if your material, or the filler wire, is contaminated with steel. Because of this, you also have to brush your material a ton with a stainless steel brush to clean if before you weld it (for some reason, stainless steel is ok).
Most of the joints that I needed to weld were pretty thick stock, so I wasn't to worried about burning through or messing anything up to bad, (in fact I had to add heat with a butane torch just to get it hot enough to weld) but the steering column tube is super thin, and I needed to weld it to a 1/2" plate, so I ended up deciding to just use a set screw instead of welding. If this joint fails later, I'll go through the trouble of welding it.
Step 9: Progress Pictures
Here are just some progress pics. These were taken around late April 2013.
Step 10: Acrylic Deck
I made the deck out of 1/4" clear-green acrylic.
I used the Solid Works model to tweak the deck dimensions, and I ended up exporting the model to a .dxf file so I could cut it directly with a laser cutter.
The not so fun part of this was drilling and tapping the 20 holes for all the 8-32 button-head screws that hold the deck down to the rails. Of corse, I didn't need that many, probably 4 or 6 would have worked just find to secure the acrylic down, but I thought having 10 screws on each side would look really awesome!
Anyways, I put two screws in on the kitty corners, then marked the rest with a centering punch. Thankfully the mill made it pretty easy to drill the holes, because for all the holes on one rail I only had to change one axis (the y axis was the same for all the holes on one rail).
Usually, I use a tap-holder in the mill chuck and tap every hole right after I drill it so the mill is zeroed right over the hole. This provides for the best tap possible, but it takes forever because you have to take the drill chuck out and swap collets and everything, and then change the z-axis height which is very tiring if you need to do this 20 times in quick succession. So, in this case though, I decided against it and just tapped by hand. My wrist was extremely sore after the last tap though, Im glad I only used 8-32 screws instead of anything bigger, or my hand might have fallen off.
I cleaned off all the cutting fluid and attached the deck! It looks awesome!
Step 11: Finishing Touches & Future Plans
I used 240 and 320 grit sandpaper on the aluminum in some places where scratches were noticeable. Then I used a Scotch-Bright pad and finished the rest of the aluminum with that, providing a nice even matte finish.
I went back over each joint and cleaned the leftover cutting fluid out of the threads of the screws and the tapped holes. Then I put Thread Lock on all the screws before reassembly.
For The Future:
As always, there are still things to work on, even though Im pretty happy with the current state of the Scooter. Here are some things I'd like to work on still, and I'll add updates as I complete these parts.
- Add battery pack and super-bright white LEDs underneath acrylic deck
- Laser-engrave an aesthetically cool and meaningful design on the deck, so it lights up when the LEDs are on
- Build the rest of the rear wheel cage so I can rest my pushing-foot on something besides the rear wheel itself
- Implement the rear pin-lock mechanism so I can lock the scooter in folded position
- Figure out some sort of braking mechanism
- Mill a slot connecting the two holes on the outer steering column so the handle bars are adjustable
- Buy better bearings for the wheels to make riding easier
- Remove more material from the inside of the steering column sleeve to decrease steering friction.