Cyclekart progress, May 24, 2009: plywood side panels
This weekend I’ve been working on the side panels for my cyclekart. There are no plans for these things, so you’ve got to kind of invent a design for yourself. I’m loosely modeling my kart after the “Delage Bequet”, but as that is a full sized car, and my kart is not a full sized car, but the driver is definitely full sized, you can’t just scale things down. There are other limitations. The body of the Delage Bequet is very round in cross section, but plywood tends to be pretty flat. So some compromises and adjustments must be made.
So, I set out to do some drawing. The first setback I came across was a distinct lack of graph paper. Well, no problem, I just made some in the Gimp and printed it out. (The menu options for making grids are under Filters/Render/Pattern/Grid.)
My first attempt at that was a failure, as I tried to specify the grid lines in inches, and the limited precision meant that things didn’t work out right. Once I specified things in pixels, things were better. At first, I tried 8 pixels per grid line in blue, and then another red grid with squares 96 pixels wide (8×12=96). The idea was each blue square would represent 1 square inch, and each red square, 1 square foot.
This ended up not fitting quite enough square feet onto a sheet of paper. But it was what I used for my first attempt at a drawing:
As you can see, the frame rails barely fit on the page, and the back end of the kart extends off the page.
So then I decided to change my graph paper so that the the blue squares represent four square inches instead of just one, thus allowing me to decrease the density of the blue lines while at the same time fitting more square feet onto a page. Here’s my second attempt at a drawing with this new graph paper.
It looks sleeker than the first attempt, but still pretty rough as I was trying out ideas trying to keep it looking nice while fitting everything that needs to fit in, esp. the driver.
Here’s my third attempt at a drawing, cleaning up the mess in the 2nd drawing. This one is starting to look pretty good.
At this point, the drawing is clean enough and good enough that I transfer it into the gimp. I used the pencil tool on a new layer superimposed on my graph paper, and just transcribed, more or less the paper drawing into the gimp. The result of that is what you see below. The shaded area represents the plywood side panel.
At this point, I start really looking hard at the design. I had two worries. First, I wasn’t sure that the cockpit opening was quite big enough. I think I could fit, but wasn’t sure about how comfortable I’d be or if I’d be squashed, or what. The second concern was that the large sprocket on the rear axle would be too big and interfere with the seat back. The second concern was alleviated when I found the radius of the sprocket with chain to be six inches.
The first concern was validated when I went out to my actual car an measured the distance from the seat to the steering wheel when adjusted properly. 30 inches, considerably more than what I’m allowing for in my kart. I adjusted the seat to allow 25 inches, and tried it out. Not good. So, I need to move the dashboard forward a little bit — moving the seat back isn’t an option — remember the sprocket. Hopefully, the aesthetics of the kart aren’t damaged too much by this operation.
I also noticed that the rear part of the panel trespassed into the area occupied by the rear axle, and that needed to be fixed.
This is the design I’ve settled on. The curved part of the side panels at the top of the rear wheels is something I’ve still not settled on, but this can be done later if I decide to do it.
And here are the side panels, realized in plywood.