Monday, December 3, 2012

Big update part 2 of 2: Finally!!

Well, it's certainly been an adventure, but I'm pleased to announce that I actually have a finished fully custom scooter frame! I'll save you some anticipation and just give you a look at the final product first:


There it is, in all its water-jetted aluminum glory. No Gorilla tape this time, I swear!

Alright, now let's dive into the juicy build report:

I started off blocking out a general shape I wanted the deck to end up looking like, using rough dimensions from my battery pack and how big I estimated a scooter should be. I wanted a slight natural curve for the deck, so I made a few splines and then tweaked them until I liked how they looked. I also disassembled my stock scooter to take measurements of the plate to fasten the front fork. This is about where I was as of my last post, part 1 of the mega scooter build series. After I had a basic shape I was happy with, I fiddled around with the orientation of the battery pack by CADing it up and spinning it around. I decided I liked the vertical orientation best because it actually minimizes the height of the scooter (which is important, considering how tall it has to be to accommodate the battery at all), at the expense of widening it a bit. I also played around with the spacing of the motor controller until I had something that was about as closely-packed as it could get.

I decided to primarily build the scooter out of 1/8" aluminum rather than 1/4" to minimize its weight, and building the entire thing out of 1/4" would probably make it a lot stronger than it actually needs to be. However, this requires some additional design considerations because 1/8" is too thin to just drive screws into its end. I ended up going with three different fastening schemes across my scooter, because each made the most sense in its own area of application. Here you can see all three schemes I used in one shot:

So, why the three different fastening methods?

I didn't want to be riding around in a pure right-angled box, so I wanted the front to have a somewhat visually interesting look, resulting in the angled nose design. The problem, however, is that traditional waterjet T-nut corner blocks are inherently 2D extrusions, which wouldn't be able to hold the separate front plates together. I decided to instead waterjet the top profile of the corner supports, and then post-machine and tap holes on the front (angled) faces.

In the middle of the body, I had a long stretch of top deck I needed to link to the sides, but I was extremely constrained by the width of the battery (I wanted to build the smallest frame I could). I decided to place 2D T-nut blocks on the outside of my side plates, sticking up into the top deck, so that they didn't take up space in the interior.

For the back, however, I had some space to spare because the motor controller has a smaller cross-section than the battery. I was able to fit in some angle brackets to hold the whole body together in the rear.

Here's a shot where you can see how the basic body all came together, this is just really an extension of the previous picture:

And another shot with transparent walls so you can see the insides:

Somewhere around here I realized that I'd probably want a brake eventually, so I just added a mount for a brake shaft to the sides near the rear wheel:

I was pretty impatient to start on the body itself, so I decided to finish the brake later and go ahead with cutting the parts for the frame.

Yaay, the magic of the metalprinter!
I decided that the easiest way to place the holes in the front end of the front plates (remember, the ones I said I'd have to post-machine) would be to just clamp the whole front assembly together and drill the holes by hand using the holes the waterjet cut from the front plates as guides.

I also went ahead and just attacked everything with a countersink, I decided it was worth the effort to use flat-head screws and not leave pan-heads sticking out of every surface on my scooter.

Here you can see the front assembly mostly complete:

I also made a slight design error and placed the nuts holding the front fork mount a little too close to the front corner blocks, so I had to bandsaw away some material to allow the nuts to clear the corner block.

Next there was a lot of tedious counter-sinking and tapping, but I was able to put most of the body together and it ended up looking pretty nice:

I had really wanted to finish this scooter for Maker Faire New York, but I was still lacking a front fork and some basic necessary components. Some attempts involved hand-drill and hacksaw insanity with my original front fork, as well as trying to fuse my scooter body with Shane's:

I didn't quite manage to get either method working, so I decided to just enjoy the fair for a while and let my scooter sit until I got home and had access to a real shop.

When I got back to Boston I started working on a brake and handlebars. I wanted a small-profile brake that would spring back, so I designed a little aluminum brake with a slot in it for a leaf spring:

I then cut it out and put it together.

And mounted it on the back of the frame.

I also noticed that I had made a small design error on my hub motor: the nylon nuts were on the same side that the wires exited, causing them to clip the wires a bit and shred off some of the insulation.

I just put some additional heatshrink over the parts that were ripped up, and backed out and reversed all of the screws holding the motor together.

I had to extend my original front fork because the much thicker deck required a lot more ground clearance. I also had a bit of a problem because the original scooter's fork is made of welded sheet steel in geometries that are really hard to fasten to. Originally I'd intended to just drill holes in the steel, build an aluminum cage around it with bolts going all the way through both sides. I had also put a couple of haphazard hand-drilled holes through the original during Maker Faire, which made things a bit trickier.

I ended up not completely compensating for the bends in the original fork, so it refused to quite fit into its intended slot. I ended up just throwing the whole aluminum cage in the mill and attacking the corners with a giant endmill. The original fork took quite a lot of coercion (of the hammering variety) until it would fit in the cage, at which point the holes were no longer in alignment. I decided that due to how solidly it was pressed in and because it's only ever really getting loaded downward, I would just leave it sans through-bolts.

I added a throttle to my original handlebars, then some wiring and loctite, and it was done! The battery, motor controller, and motor were all identical to the previous iteration, so it handled about the same as the sketchy Johnscooter conversion, but it certainly felt better not having the battery just taped onto the deck.

Hopefully I can post a video of it cruising soon.

I've also spent the last month starting two new major projects, so I'll have posts for those written up shortly!

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