Cody provided the first pass at the Electric Handcycle, as shown in his email below. It is interesting to see how he approached, which I think is better than what I did in my Sketchup experiment with Geoffrey. While we both used a 55 degree head angle, Cody fixed the trail at the same as the Travel Bike. In my Sketchup model, we used 55 degrees, but also set the pedal offset at 4”. Cody let the pedal offset float as needed. See the end of this blog post to see why Cody’s method is better.
Hey Bill,I was able to spend a little time today on the handcycle.Anyway, I set out to start to get the geometry of the electric handcycle to start to make sense and see how everything fits together and relates. I started with the travel bike and started with adjusting the geometry for a 20" wheel. I decided to keep the following constant:- Head tube angle (55 degrees)- Amount of trail (.981 inches)- Wheelbase (50.375 inches)- The position of the pedals in relation to the position of the seat- Seat height off of the groundEverything else was up for adjustment.
I found that as I moved the front axle up (necessitated by the larger front wheel) the pedals moved forward. So, the seat moves forward as well to maintain the same relationship. This has the added benefit of putting more weight over the front wheels which should help with traction.To maintain the same amount of trail, the headtube/steerer offset changes to a little under 5 inches.
You will also notice a little L-shape near the bottom, these are the footrests. Since we didn't take this geometry from the travel bike, I took it from the NEH. I think it will be important to have that in the model to determine how to place the miter in the main tube.Moving forward a little bit I roughed in some tubes, using the same diameters as the travel bike.
I found that the miter in the main tube is probably going to be a requirement. Since the increased front tire diameter would otherwise increase the height of the main tube by almost two inches, it would be very difficult to get your leg over the main tube if it were not mitered. I just kept the main tube horizontal in this version which works well aesthetically I think.
If we were to use a continuous main tube, rather than a mitered one, this is what it would look like.I would imagine this gives it more of a rakish look than you were going for.
I also know you didn't want a bent main tube for aesthetic reasons, but it was easy enough to model it, so I made a quick version like that
Probably difficult to get a good idea at this point but as we get more detail in there with wheels, crank, etc. we can play with these things some more.Next up, I'll be going to the shop tomorrow so I can get some good fork dimensions and start to design the whole pedal/steerer assembly in a bit more detail.Let me know what you think so far.Cody
I went into the Sketchup model from the prior post, and extended the head tube axis to the ground. Somehow I thought we’d have very little trail, but in fact with the Sketchup model we have 2.2 inches of trail, which is becoming more than we want. Even as much as I’ve been thinking about this, my mental picture was 180 degrees off. Having a smaller pedal offset will INCREASE trail because it pulls the head tube up, and thus makes the extension of the steering axis hit further ahead of the contact patch, thus increasing trail.
Requires Sketchup 15. Download here: http://www.sketchup.com/download
