Saturday, July 6, 2013

Building a µGP racer. Day 3..

After the depressing evening that came from build day 2, I took a bit of a break.

The new motor was ordered.  I decided not to return the materials I bought.  And went back at it.

Speaking of materials, how's this for a start:

Tonight I mocked up the new motor, and found that it will work!  I need to buy a lot more #25 chain though.

I think it looks like a good fit.  The chain actually clears the BB, so can run roughly whatever size sprocket I want.  ... Though that will likely need to be specified at some point.  But hey, we're still in development right?  

So what's a motorcycle with a bicycle seat?  A moped.  This isn't a moped.  Tonight I started fixing that.  

The rule I'm going with for now, is that all saddles must clear the tire by at least half an inch, and the back of the saddle, or tail-section, must be within 1" of a vertical line drawn from the rearmost point of the tire.  AKA, you saddle needs to be long enough to cover the rear tire.  

The build began with a 6" wide plank of 3/8" plywood.  It's 24" long, but i'm sure it'll lose an inch or so off the front end eventually.  

You can see the layout lines I made so I could be sure that my hole for the seatpost is centered.  For the record, most BMX bikes have a roughly 1" seatpost.  So a 1" spade bit does a heck of a job.  

Mmmm power tools.  That drill press was the first "serious" bit of metalworking gear I bought.  I needed something vaguely precision so I could mutilate peoples expensive paintball guns.  It's amazing that it's still around after all these years.  

I drilled the hole from both sides.  So that there was no tear out of the exit side.  

The back end of the seat is going to be supported on a metal bridge.  The bridge will also provide the lateral support on the seat.  To find out where that bridge would go on the seat, I used a level, and measured from the seatpost to the back axle.
I had initially planned on using the axle bolts to hold that on. Seeing how big my track ends are on the bike, I'm just going to drill mounting holes into track ends.  

I don't have any pictures of the bridge construction.  I'll get those later.  But here's the saddle on the bridge.

Next time?  We'll be finishing the saddle, and bridge.  That means getting it trimmed to shape, and covered.

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