Working with Geoff Bostwick SketchupTutors@gmail.com we were able to add a proposed seat design to the Electric Handcycle design. The Sketchup model is available at the end of the post. You can download it and play around for yourself.
This 1982 photo shows me on the first handcycle I designed. It was based on my 1980 undergraduate thesis at MIT. We’re stealing part of the seat design for the Electric Handcycle, some 36 years later.
In this scale model made of brass (I was very proud of that), I proposed a square main tube and two sliding seat supports which would clamp to the main tube. In the end we used round tube, and round clamps. It worked fine, and I rode that bike for years.
If you feel like it, here is a whole bunch of photos of the brass model and photos of the actual thesis handcycle before painting.
The proposed seat will use round clamps over the 2” metal tube. The seat will be able to move from to back. But that’s not really the point because the front end isn’t adjustable, and the seat will end up where it due to the geometry we pick on the front end. We may have an adjustable reclining angle for the seat, and that would mean moving it front to back.
The Travel Bike uses steel clamps over a titanium tube. It works great. Titanium is like gold — it doesn’t corrode at all. We may use titanium for the main frame, which will make clamping very easy, whether the seat is also in titanium, or if we use chrome-moly.
The first prototype will be all chrome-moly. The clamps should work fine. Yes, clamping will scratch the paint, but if we go with titanium, no pain on the main tube (or that part of it) is required.
Here’s the clamp, but with no bolts or anything. When finished, there will be a top piece and a bottom piece. They’ll bolt together.
NOTE: This is far from a finished design. This is meant to get the concept going.
Here we see the current Sketchup model with the Solidworks model dimensions overlayed. The seat is positioned correctly, but you can see that front end is about 1 inch further back than the Solidworks model calls for. Not a big issue right now, but we’ll need to sync up with Solidworks once we finalize the geometry. For example, or recent work has the head tube angle at 54 degrees, and the pedal offset at about 5”.
You can download the Sketchup Model below. (Uses Sketchup 2015 or later)