Didn't the Robin have a small wheel size, so requiring a low ratio? What did the Mini have, for 10" wheels?
On gearboxes, I watched some of the Formula-E coverage last night, more for the Buenos Aires connection rather than the E part, but there it was mentioned that the cars had gearboxes to maximise the use of the maximum allowed motor speed of 20,000 rpm.
Take your pick...
somewhere between 3 and 4:1 it seems.
Yup. electric motors have optimal RPM like almost anything else.
its a different curve to IC, but its still a curve.
And since, as has been observed, electric motors have maximum torque at zero rpm, then any method of running them closer to that speed must be good. A gearbox would seem to fit that quite well.
They weren't big, that's for sure but I don't think they were much smaller than many similar vehicles of that time. So, probably 10 or
12" probably?I think the early ones were 10" and then they went to 12".
Do you remember if they actually use them like gearboxes (changing gears all the time) or just / mostly leaving them in one gear?
I think that the needs and design of a racing car (where you are looking to optimise everything) may override the more pedestrian use of something like a road car in most cases. ;-)
Cheers, T i m
I didn't watch the race, and I doubt whether that would have been obvious anyway. I found the website useless when I was trying to find out, in advance, where in BA the race was held, so although I would normally suggest the site as the place to look, I am not encouraged!
Some elecric motors have max torque at zero revs. Not all.
I have watched a couple of the races and they sound so much like when I was racing RC electric cars myself (Yokomo MR4TC). ;-)
Listening to the FE in-car audio here:
... it sounds like there are gear changes. ;-)
Cheers, T i m
I'd be surprised if Reliant made the unit. And if not, it's likely the diff at least was shared with other makes.
The owner's club would be the place to ask.
Sorry, how are those statements connected to your assertion that "So bhp/ton for ICE engines is neither here not there"?
Power to weight ratio is a reasonable way of getting a feel for the straight line performance of a vehicle regardless of its propulsion technology. If the bhp is quoted at the wheels, even better (although losses through modern gear train are unlikely to be huge).
The 13 second 0-60 for your car is comparable to other vehicles with similarly low power to weight ratios, even if the acceleration curve may be a different shape.
Not all electric motors have maximum torque at zero RPM. A pure DC series wound type does, though. But not sure how good that would be for continuous running.
Cyclists are very quick off the mark as well, up to about 10 mph. I would still not bet on one in a drag race.
at about 2:26 he says "the gearbox works fine, up shifts, down shifts" or words to that effect.
Yeah, and you can hear the changes etc. But you can also hear those motors revving fairly well (was 22k RPM?) so as has also been mentioned they may need to keep them up in their sweet spot.
If my EV had a std Reliant (3 wheeler) diff, 12" rims and does 30mph I'm sure we could work out the peak RPM in that and I feel sure it's nowhere near 22k. ;-)
If you press the accelerator gently you get 12V on the motor (and
800Ah available) and the car pulls away reasonably smoothly (about the same as anyone not 'racing' away). However, if you floor the throttle from standstill (48V @ 200 Ah) it pulls away pretty smartly, even from the 0 RPM level. It would probably be a bit quicker if there wasn't quite a few meters of fairly heavy copper cable and contactor contacts in circuit. ;-)Cheers, T i m
At zero RPM the power output is also zero. The torque is about as useful as the force holding the car off the ground.
You want maximum power for performance; contrary to popular belief torque is merely a by-product and not useful in itself. (if you don't believe me BMW have a good range of petrol and diesel cars, and publish the performance figures; performance goes with power, not torque)
But you're probably also interested in maximum efficiency, as range is such a problem, and for that a gearbox might help. But so might some clever electronics. I'm no expert on that.
Andy
It was said that the limit was 20,000, but who knows?
Power is merely a function of torque and engine speed. If a torque figure is maintained. the bhp would simply go up with revs. But it drops off after the peak figure which is usually below peak bhp. And usually pretty quickly after that.
For a road car, a nice flat torque curve is far more important than an artificially high BHP figure.
Agreed. I used to have a car which had no useful torque below about
3,500 rpm engine speed. Once up to speed, it was fast, but from a standing start, it was terrible, until the magic engine speed was reached. Torque dropped off, but since the engine was now running fast, it had plenty of power. Power is indeed the result of torque multiplied by engine speed, and performance can be different things to different people.
ROFL!
Er... why is it any easier to run that than to just run the engine?
What about all these fuckwits who use daytime running lights (on a sunny day!) that are more powerful than a dipped beam? That'll never work in an electric car.
cs for traction.
In an urban situation, you never get anywhere near 60mph. And there are no gear changes.
The one in the middle is similar to the motors fitted to electric cars.
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