Observations on performance and gearing

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reikiman's picture
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Observations on performance and gearing

I have a Charger bicycle that has been an ongoing project for a long time. I've finally got it in great shape and am having some fun riding it around. Instead of the 12v 12ah SLA batteries it was designed for, I have a 24v 10ah LiFePO4 pack from pingping which fit into the bay for ONE of the batteries it replaced, hence it has the same energy capacity at half the size and weight of the previous pack. Very cool.

I've also replaced the stock controller (because I blew up the old one) and that meant for a long journey during which I learned what a bottom bracket is etc. But that's to be told another time.

The design is a REVCOR motor (the same kind as was used for the ZAP DX kit and the EV Warrior) which has a direct chain drive connection to the rear wheel. The controller is a Yi-Yun 24v ?500 watt? model. The rear wheel has a Shimano Nexus internally geared hub. This means the motor power is geared unlike many other electric bicycle designs.

In typical electric bicycle design the motor is not geared .. either it's a hub motor (no gearing) or the motor connects to the wheel via a different sprocket than the derailleur.

Because the motor drive train is geared you can vary the gearing ratio while riding for different purposes.

Using a Cycle Analyst while riding on flat terrain (no pedaling) I noticed the following performance figures

  1. 2nd gear: 12-13 miles/hr max, motor high RPM (high whine)
  2. 4th gear: 400 watts, 14-15 miles/hr max, motor at lower tone (lower RPM)
  3. 7th gear: 500-600 watts, 18+ miles/hr, motor at lower tone (lower RPM)

The speed in the top gear is impressive, and it poked above 19 miles/hr a couple times.

Just because electric motors have a wide power band doesn't mean varying the gear ratio has no benefit. On this bike it doesn't start very well from a stop in 7th gear, but you could start in 4th then switch to 7th when at speed. Also hill climbing probably works better in the lower gear but I can't test that around here.

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