Tuesday 28 January 2014

Overvolting bike.3 - part 2

First, I repaired an old speedometer whose wire had snapped, and installed that.

Then I tried to take the handlebars off the bike (which I'll have to do to put it in the car). You remember I replaced the disc brake on the front wheel with a caliper, because the motored wheel couldn't take a disc ... well, I used a cable that was a bit too short. The brake worked fine, but the brake cable wasn't long enough to let me unmount the handlebars. Grrrr. So I replace the cable with a longer one (and had to do it again because when I cut the outer to the right length, I stupidly cut the inner too, and thereby wasted an inner cable. Annoying, but those inner cables are only a few pence. And now the bike was ready to test. By the way, bike.3 is 7 pounds lighter than bike.1, the bike I'm currently using. That's a nice thought, for when I'm lifting the bike over obstacles.
First I measured the speed with the existing batteries (8 cells), which, being freshly charged, were 33.6 volts. With the front wheel held above the ground, that came to 21 mph. That, of course is the speed with no load; with a heavy rider on board (me) that would be a lot less. But useful for comparison. That gives me a reference point.

Then I plugged in more volts; 12 cells, which comes to 50.4 volts. I was expecting my voltmeter to give up, it's only supposed to go from 0 to 30 volts. It only cost about £1, so I wasn't that bothered if it broke. But it didn't, it showed the voltage correctly. That's nice.

Then I ran the bike, again with no load. This time I got 32 mph - again, that will be a lot less with a load. But it does indicate that giving the bike 50% more battery, means that I have 50% more oomph. What I'm interested in isn't speed, it's torque.

When I'm caching, I'm biking from cache to cache, typically 2-300 meters; 500 meters is a long gap. I don't need speed, Even at 12 mph, that's about a minute. It takes me longer than a minute to dismount, prop the bike up, and remount; finding the cache can be anything from a few seconds to 20 minutes. So speed isn't important, because even if I biked at 24 mph, I'd only be saving half a minute per cache. And anyway, when I'm going over rough ground such as many bridleways are, I probably do a lot less than 12 mph.

What is more important to me, is torque at low speed. Torque is what pulls me up hills, and over rough ground, and gets me through squishy ground. So this looks like rather good news; I can add 50% to my torque without (I think) any cost.

I have to try a longer run, to see if the motor or controller starts to get hot, And I'll try it out on a local hill. And I also want to try it with 16 cells (67 volts). To do that, I have to make up a new wiring harness that puts four of my Hobbyking batteries in series, and I'm waiting for the various connectors I've ordered for doing that.

Tomorrow, ladysolly is out till late, so I will be also. I'm going North to Nassington, there's a couple of circuits there that are calling me.

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