ShortHopper electric bike takes shape

July 23, 2010 · 5 comments

This ebike frame is complete. There is a lot of finish work left to do. However, I couldn’t resist building it to the point where I could go for a test ride.

First I had to build the front wheel. There is a video of this in the works. I hope to post it soon.

Next I finished the build enough to roll and stop and pedal in first gear.

I managed to get a short test ride. Since the internal hub shifter isn’t hooked up I’m stuck in first gear. Once I get the shifter installed I’ll be able to get up to speed and go for a longer ride.

The short ride I had was interesting. It felt very nimble and quick turning, maybe too quick. I’ll know more when I can shift into a higher gear and get some speed up. I can turn on a dime. This will make it easy to navigate a crowded downtown peloton but might make it too twitchy for higher speeds.

You can see the final geometry in the photo. The laid back seat tube angle stands out. The space between the seatpost and rear wheel will be filled with a battery/controller box.

The reason for the seat post angle is because a complete donor rear triangle from a 26” bike was used. For a 20” bike, the bottom bracket is higher than a 26” bike. This decreased the seat tube angle to 65 degrees.

There is plenty left to do. I have to choose an electric bike conversion kit and install it. I’ll make a video of that.

I also need to design a battery/controller box to hide those things and their wires. It will be similar to the one in the Chop Mountain Bike project, same idea anyway. Probably construct it lighter this time.

To read all of the steps for this project so far go to the ShortHopper category.

I’m still deciding which electric bike conversion kit to install. If you have a recommendation, please leave a comment. Any other comments about this design are welcome too.

{ 5 comments… read them below or add one }

1 danr July 23, 2010 at 6:47 pm

looks great! that rear derailleur looks like it might scrape on a right turn if extended all the way.

2 pdxebiker July 23, 2010 at 6:49 pm

I have a folding bike with similar geometry and wheel size. It’s great for what it is, but it’s not a daily rider. That said, an ebike conversion kit could make a big difference.

3 Dan July 24, 2010 at 3:07 pm

@danr – I just threw that derailleur on as a chain tensioner for the internal gear hub for now. That way I can keep the chain long until I decide what the final drive train will be. If I go with a rear hub motor, I’ll put a better derailleur on. If I go with a front hub motor, I’ll loose it altogether.
@pdxebiker – I’m hoping that this bike will be a daily rider. I might have to redesign it a few times to get the geometry right though.

4 Jim N. August 12, 2010 at 1:44 pm
5 Dan August 12, 2010 at 3:56 pm

It does look like yours except yours looks much better. How do you like the way it rides? I didn’t get the HT angle right on mine so it feels really twitchy. It’s just an experiment. I hope the next one rides better.

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