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Sunday, July 24, 2011

R&D is expensive

Yet another lesson learned from this project: R&D is very expensive.

The tire glue didn't work. It might have been because the metal was too smooth (it really wasn't that smooth...), or wasn't properly prepared. But for whatever reason, as soon as I took the hose clamps off, I got to watch the polyurethane slowly peel back from the edges. Damn.

Note the bubble made it into the steel.

20 minutes later...

Apparently, urethane strip's natural position when wrapped around something is warped:

, which is probably why it peeled up. I doubt any amount of glue will be able to hold that down in the long run. So, options:

1. Try prepping the surface better and re-glue.
2. Try thinner polyurethane strips.
3. Cast tires (so the warping problem goes away)
4. Cast tires with attachment mechanisms embedded in them (solves both warping and mounting problems)
5. Find a wheel to bore out and glue on (so I don't have to cast tires)
6. Screw on the polyurethane strip (see below).

I seriously doubt 1 and 2 will work judging by how poor the bond was this time. 3 and 4 require expensive casting equipment (hey, R&D is expensive...). That leaves options 5 and 6.

Let's start with option 6.

The idea is to have 8 of these "tire-retainer" rings waterjetted. They would bolt to either side of the motor using the existing bolt hole patterns. The extra set of bolt holes would have #4 sheet metal/wood/self-tapping/self-threading/sharp-pointy-things go through them and into the sides of the polyurethane tires (that are hoseclamped on to the wheel during this process). Screwing into the polyurethane works great:

Unfortunately, having the 8 plates waterjetted would cost me $120...ouch...again, R&D is expensive. Let's try to find something cheaper- on to option 5!

Now, it just so happens that I made the OD of the hubmotors 3.25"...which happens to be exactly the maximum ID you can bore out 125mm scooter wheels to. Check it out:

Alien Wheel!
I'm going to try to press fit three scooter wheels per motor. I bought 12 off of ebay for $65 with shipping. We'll see what happens.

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