Chris Kouba
Supporter
Chapter One: Mental Commitment, Design Definition, & Initial Build
Portland has an adult soapbox derby each summer (http://www.soapboxracer.com/) and an acquaintance of mine built an entry and ran it last year, having a BLAST. I found out about it and decided I had to do it, so I started my build this fall...
My design concept:
Pondering the build for a while, it seemed like the fewer the bearings, the lower the friction losses might be (although this will increase the loading per tire). I chose a reverse trike layout, hiding the single rear wheel behind my fat head instead of putting two rear wheels out in the air stream. That pretty much laid out the design for me- narrow, low, 2F/1R trike. In my head, I saw the front half of a Swift DB1, except lower and narrower, with a single 26" wheel behind the cockpit.
What wheels should I use? I wanted something which offered minimal rolling resistance, had reasonably robust bearings, was secured by an appropriately-sized fastener, and was available cheaply. For the front end, I found them in the shape of a used wheelchair (acquired off Craigslist for $20). For the rear end, I enlisted the front wheel from one of my mountain bikes, complete with 8" rotor and hydraulic brake.
Beside that, all I needed to source was steel. This was easily done as there's a steel yard maybe 12 minutes from the house.
I read somewhere that one of the early British GP teams (Cooper?) designed their entries by drawing on the shop floor with chalk, so I figured this was good enough for me. I moved the GT out of the way, ran the broom around the floor a bit, and got on with the task at hand.
With the wheels set up just inside 48" wide and the rear wheel placed roughly along the centerline, I laid out the space which my body would occupy in the chassis. Then I narrowed it a bit. I made sure the fronts of the front wheels were slightly behind the front of the chassis (roughly 8' from the aft of the rear wheel) to ensure the whole thing would fit in the truck bed. It looked a bit like this:
I then started chopping steel. First thing to do was build the front axle. I wanted to be able to store the car with minimal footprint, so I wanted an axle I could simply remove and then stand the car up in the corner or something... to get it out of the way. This axle will be held in with U bolts secured to the frame. The upright would be a simple machined billet alu piece with the wheel bolted to it with a 1/2" bolt, and it'd pivot in a C channel section of steel. It would look like this:
Front end solved, I turned to the rear end. I was using a 20mm thru axle wheel, so I just machined up two pairs of pillow blocks with a 20mm hole, and put another set of holes in them so they can be bolted to the frame. Kinda like this:
I then built a very simple fork, which became the first member of the actual chassis:
Presumably you can see where this is going... Once the fork was made, it didn't take much to connect it to the front axle- just a bit of box tube:
And by the end of the first day, it looked like this:
Yeah, still needs steering and brake mounted, floor boards, seating, bodywork, nosecone, etc... but it was off to a great start if for nothing more than proof of concepts.
Chris
Portland has an adult soapbox derby each summer (http://www.soapboxracer.com/) and an acquaintance of mine built an entry and ran it last year, having a BLAST. I found out about it and decided I had to do it, so I started my build this fall...
My design concept:
- Fit in my truck bed- so a footprint of 4'x8' or less
- Completely removable front axle assembly
- Lowest possible rolling resistance
- Minimal cross-sectional area
- Good brakes
- Simple
- Strong
- Heavy
Pondering the build for a while, it seemed like the fewer the bearings, the lower the friction losses might be (although this will increase the loading per tire). I chose a reverse trike layout, hiding the single rear wheel behind my fat head instead of putting two rear wheels out in the air stream. That pretty much laid out the design for me- narrow, low, 2F/1R trike. In my head, I saw the front half of a Swift DB1, except lower and narrower, with a single 26" wheel behind the cockpit.
What wheels should I use? I wanted something which offered minimal rolling resistance, had reasonably robust bearings, was secured by an appropriately-sized fastener, and was available cheaply. For the front end, I found them in the shape of a used wheelchair (acquired off Craigslist for $20). For the rear end, I enlisted the front wheel from one of my mountain bikes, complete with 8" rotor and hydraulic brake.
Beside that, all I needed to source was steel. This was easily done as there's a steel yard maybe 12 minutes from the house.
I read somewhere that one of the early British GP teams (Cooper?) designed their entries by drawing on the shop floor with chalk, so I figured this was good enough for me. I moved the GT out of the way, ran the broom around the floor a bit, and got on with the task at hand.
With the wheels set up just inside 48" wide and the rear wheel placed roughly along the centerline, I laid out the space which my body would occupy in the chassis. Then I narrowed it a bit. I made sure the fronts of the front wheels were slightly behind the front of the chassis (roughly 8' from the aft of the rear wheel) to ensure the whole thing would fit in the truck bed. It looked a bit like this:
I then started chopping steel. First thing to do was build the front axle. I wanted to be able to store the car with minimal footprint, so I wanted an axle I could simply remove and then stand the car up in the corner or something... to get it out of the way. This axle will be held in with U bolts secured to the frame. The upright would be a simple machined billet alu piece with the wheel bolted to it with a 1/2" bolt, and it'd pivot in a C channel section of steel. It would look like this:
Front end solved, I turned to the rear end. I was using a 20mm thru axle wheel, so I just machined up two pairs of pillow blocks with a 20mm hole, and put another set of holes in them so they can be bolted to the frame. Kinda like this:
I then built a very simple fork, which became the first member of the actual chassis:
Presumably you can see where this is going... Once the fork was made, it didn't take much to connect it to the front axle- just a bit of box tube:
And by the end of the first day, it looked like this:
Yeah, still needs steering and brake mounted, floor boards, seating, bodywork, nosecone, etc... but it was off to a great start if for nothing more than proof of concepts.
Chris
