Transmission losses

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qdos
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Postby qdos » Fri Aug 22, 2008 8:57 am

Not to worry Nino, threads often wander.

The Fiesta by the way was owned by Chris B and I'm sure he will let you know what the set up was in it. It now belongs to Alan Ward the former Chairman of the BVS who often writes items for our magazine, Plugged In, about the Fiesta

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EVguru
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Postby EVguru » Fri Aug 22, 2008 9:24 am

No, not that Fiesta.

Chris's machine had two motors driving through the original gearbox. In first gear it would probably climb anything it could get grip on.
Paul

http://www.compton.vispa.com/scirocco/
http://www.morini-mania.co.uk
http://www.compton.vispa.com/the_named

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qdos
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Postby qdos » Fri Aug 22, 2008 9:41 am

Ah wrong Fiesta sorry, still I'm sure Chris or Alan would be happy to talk about it. there's also JC's Peugeot 205 I don't know what's in that one.....

MalcolmB
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Postby MalcolmB » Fri Aug 22, 2008 10:53 am

Thanks for the tip about the inverted chain drives Jeremy, I'd not heard of them before. Unfortunately they're not reversible though.

Didn't know the Prius used a chain drive either, that was a surprise. Duplex or triplex drives make sense, but I'd still have to go down to 8 mm pitch chain to get a small enough final sprocket. Sounds a little flimsy. It's hard to get a good feel for what will be a "good enough" solution. When you look at manufacturers' design recommendations they're clearly very conservative, otherwise the big bikes that are on the road now wouldn't get away with chain drives.

I'd rather avoid oil baths and oil seals if possible, although I'd naturally fit chain guards to keep out the worst of the muck. Does anyone know how effective modern chain waxes are?

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Jeremy
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Postby Jeremy » Fri Aug 22, 2008 11:07 am

The specs for industrial chain drives tend to assume that the thing will be run at rated power all day, every day, will probably not get as much care and attention as it should and will have a service life that's many times longer than the chain and sprockets on a bike.

Chain drive ultimate torque limits are set by the bearing stress wear limit of the rollers, normally, and are much higher than the figures given in the industrial design catalogues. An electric motor driving a vehicle is a fairly benign application, as the power duty cycle is very low. Average power is only a small percentage of maximum power. Using the SFC figures for the ICE on my Prius I worked out that it's average power consumption was about 8 or 9hp. Not much, really.

Even just building a simple case to keep the dirt off will very significantly improve the chain life and reduce the maintenance requirement. Some of the old enclosed chain bikes had extraordinarily long-lived chains and sprockets, and they only used simple bits of bent tin to "seal" things. I doubt you'd need to go to the bother of oil seals, even with an oil bath in the bottom of the casing. You could probably get away with the "oil slinger" effect of the sprockets themselves to stop oil getting thrown out.

If you opted for just chain grease/wax, then it should be possible to build in a simple "squirt tube", aimed at the chains. Periodically squirting an aerosol of chain lube down this might be all that's needed.

Alternatively, you could look at adding something like a Scott oiler above each chain, and having a small catch tank for waste oil underneath that needs emptying now and again.

Jeremy

MalcolmB
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Postby MalcolmB » Fri Aug 22, 2008 11:32 am

Many thanks for the advice! I'm pretty sure this is the direction I'll be heading.

Deker
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Chains n Belts

Postby Deker » Sun Sep 14, 2008 11:05 pm

Hi there.

Chains, great advantage is you can achieve wider ratios in one step, compared to HTD or other type toothed belt drives.

HiVo or inverted tooth, MUST be run in oil, are expensive, and HiVo toothed gears must be mounted on very parallel shafts, they will not tolerate mis-alignment.

Toothed belt, for continuous duty, cast iron or steel pulleys give the best long life performance, you should always use an iron pulley (the smallest pulley) on the motor, in our application weight is an issue, so you may use an Aluminium or composite on the larger pulley.

I have seen aluminium toothed pulleys so badly worn that the belt does not make full contact on the mating faces of the pulley.
This leads to premature rupture of the belt.

Deker

bobc
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Postby bobc » Mon Sep 15, 2008 11:58 am

Researching for the greenpower racers, I found a "human powered vehicle" report on transmission losses. The interesting fact from this was a massive increase in losses if any sprocket has less than 12 teeth (i.e.start to see a 2-3% increase in losses c.f. 13/14 teeth)


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