Archive for March, 2008


Demise

Saturday, March 15th, 2008

Unfortunately the bike took a lot of abuse in the past week. I took it to the San Jose EAA meeting on March 8th where it received a good deal of attention. I left the bike at work because this week I moved into a house in San Mateo and began setting up the garage. We rode the bike around at the office until a high speed run into a speed bump broke the handlebars off. A subsequent fall damaged the battery box on one side and bent the crank assembly at the end of the extention tube. Rather than fix the bike, I decided to build another bike with a full suspension and some meters so I can finally make good quantitative measurements.

Max speed achieved: 21mph

Max speed achieved in one “short” block: 19mph

Average speed: 13-15mph

More Test Rides

Monday, March 3rd, 2008

I build a head mounting for my Canon HV20 using a bike helmet, two large washers, a 1/4″ bolt, and two 1/4″ nuts. I used a small bicycle lock to make sure that if the camera fell off anyway, it would not fall far. I then rode both bicycles around to record the experience. This SWB bike could do with some adjustments to feel more like the LWB bike. The lower handlebar and pedal heights especially improve comfort and visibility. The SWB bike handles turns far better however.

Lithium Batteries and Generator Testing

Saturday, March 1st, 2008

I dropped by Halted and GreenEmotor. Allen Chen had a lithium battery pack ready for me, so I went home and tried to charge it. Unfortunately the charger blew up the moment I attached it to the battery pack. Not quite sure what happened there, so instead I took the pack of 8x 3.2v 12ah cells and charged them with the old UPS by charging 4 at a time. The lithium ion cells are rated at 3.2v, but they actually top off at about 3.9 or 4.0 volts, and some had dropped to 2.8 or so. I left these charging for several hours

March 2nd

I made some rough tests of the generator motor. They reveal a bit of a problem.

Pedaling Cadence (rpm) Current (A)
50 0
60 0
90 1
150 5
burst 10+

FYI, 60rpm is a nice leisurely pace. 90 is fast paced, while 150 is frantic. These results are not surprising. The battery voltage is 24v, so below that, there is no current flow. In some earlier testing, I was able to generate 36v by pedaling hard. That’s 12v at roughly 10a (actually a bit more, as the meter topped out at 10), or 120watts. Since the LWB recumbent took 350w of energy to travel at 25mph, and that was about as fast as I could go on it, that gives an efficiency of less than 50%. Not good, but not surprising.