About Cam

gribbly.org* is the online home of Cameron Brown. Creative director, designer, musician, mediocre programmer, caffeine addict. Seattle

This is where I accumulate interesting links... If you're looking for coherence or context, you're in the wrong place!


The Electric Cruiser Project - Part 1

OK, so I bought an ex-Venice Beach rental cruiser back in 2001, for ~$40. I just finished a thorough mechanical refurb today. Stripped it down to the frame, cleaned and adjusted everything, and put it all back together. It rides more sweetly than it ever has, which is good news!

Now I want to electrify it =] I don't know how to do that. But I'm going to learn.

First, research. Tonight I found this link , which answers some basic questions for me:
  • "In my opinion, a bike needs a motor of at least 400 watts and probably not more than 1000 watts. The reason for a motor this powerful is simple: hills. You need from 5  to 10 times as much power to go a given speed on a decent grade."
  • The motor he used "draws around 41 amps while producing a continuous 1 hp. Put a greater load on it and will draw well over 100 amps and produce up to 3 hp."
  • Electric motor: 3000RPM+
  • Bike wheel (26" @ 20mph): ~265RPM
  • Therefore a gear reduction of ~11:1 is needed.
  • "Now it is certainly possible to simply bolt, say, a 130-tooth chain sprocket to the rear wheel and drive it with a 13-tooth drive sprocket off the motor. But this is a very large wheel sprocket (about 15" in diameter) and, critically, the chain would be unbearably noisy. My basic observation about chain drive is that if any chain sprocket turns faster than about 750 rpm, it will start to make a racket."
  • His solution is to go motor -> belt -> "jack wheel" -> chain -> rear wheel. Seems to work well, and kind of looks like a supercharger =]
  • Rear wheel sprocket is on the left, and is just clamped to the spokes! Apparently that works fine.
  • "My battery pack has 2 x 12V x 16Ah = 384 watt hours"
  • "A bike can easily draw enough current to discharge a battery pack fully in under half an hour, so batteries will not give their rated output under these conditions."
  • Recommends AGM.
  • "I feel that a decent controller is absolutely necessary with a powerful motor like this."
  • "You need to size your controller at about 3 times the rated power of your motor. My motor is rated at 41 amps continuous, HOWEVER it will draw a lot more than that at full throttle under load."
  • Regenerative braking: "Almost certainly never worth the added trouble, expense, and operational hassles. You would be much better off with a freewheeling setup."
  • "The brakes can easily overcome the motor in an emergency stopping situation." <-- good to know =]
  • "I can also see going to a higher voltage system. 36 or even 48 volts would be a lot better and keep the current draw down."
  • "Stay away from friction tire-drive - too much slippage and tire wear"
  • "Stay away from chain drive - at 3000 rpm a chain is too noisy"
Some interesting motors:

Handy info: