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Have you made or bought a converted vehicle if so this is for you
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EVguru
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Postby EVguru » Fri Aug 15, 2008 11:58 am

I presume we're talking about a series wound motor.

is there any simple way of estimating amps/torque at different rpm from a single operating point?

No.
Looking at performance curves for a motor of similar size and weight the torque values at various currents are:
130A = 13 ft lbs
260A = 33 ft lbs
390A = 57 ft lbs
so, it's not a linear relationship?


No, it's not. In theory there is an exponential relationship between current and torque (becuase both field and armature currents go up).

There is a mathmatical model for a series motor, but there are quite a lot of factors and the manufacturers don't publish them. If you have graphs, then you can calculate the factors and use them to determine figures outside the graph (different voltages, currents off the graph, etc.)

There is an EV calculator that with some care can give useful results and I has a motor calculator;

http://www.geocities.com/CapeCanaveral/ ... vcalc.html
Paul

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

MalcolmB
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Postby MalcolmB » Fri Aug 15, 2008 1:46 pm

Thanks Paul

Yes, it's a series motor. I've played with that calculator before, but I don't have enough data to get any sense out of the motor calculator.

You can have your thread back now Chris :)

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geekygrilli
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Postby geekygrilli » Fri Aug 15, 2008 7:38 pm

No worries!

Thanks for all your comments, much appreciated.

The motor is dimensionally large, and blimin' heavy. Running at 96v it does get warm, but never hot. I has 47v stamped on it, which is odd.

I've been doing some thinking about how to extend the range...

I think I have a lot of inefficency in my gearbox. 2nd gear is very noisy and also a little short for driving at 30mph. I'm on the look out for a cinquecento sporting 'box whch has different ratios. Its only an hour's work to replace it, so its worth a try.

The coupling isn't great, and makes a little noise, so its probably a little out of line (It does have float in it, though). It should be silent.

The tyres are wider and a higher profile than standard, but they were new and on the car when I got it. I can't see LRR tyres paying for themselves within 3-5 years. Maybe I am wrong. With the tyres I have on I can carry quite a lot of speed through corners :lol:

Wheel bearings are all in good condition. Brakes are not binding.

The controller is under the seat, so the motor wires are 4 times longer than thy need to be, they do get warm. I couldn't package it under the bonnet as there was just no space.

The car is very basic and carries no extra weight. I don't want to rip anything out that stops it looking and feeling like a real car. However, personally I have lost 5kg in the last month :D

My driving style really is the biggest loss/variable and I want to measure how this can affect the power consumption. I accelerate nice and slowly, but not slow enough to be beeped by other road users.

Any other ideas and areas I can look at would be greatly appreciated.

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qdos
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Postby qdos » Sat Aug 16, 2008 8:29 am

Driving style makes a big difference. It's mainly the stopping though not the accelerating which can make a big difference. Think well ahead and think about the speed you want to be at in 10 seconds time and coast to junctions etc. don't drive to them and then put all that kinetic energy in the heat transformers (breaks)

It pays of just as well in an ICE car too so everyone can practice this :) Oh and modifications to the right foot are free too ! ;)

hyve
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Postby hyve » Sat Aug 16, 2008 9:37 am

Have you looked at wheel alignment, Chris ? On my Fiat the book says up to 4mm toe-out at the front. Better handling for fwd, maybe, but not good for drag.
Experiment towards zero. Don't forget the rear too. Old car = possible abuses.

Otherwise congratulations for just getting on and building the thing, not like me, sitting about trying to design it perfect.
Peter Ph

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EVguru
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Postby EVguru » Sat Aug 16, 2008 8:02 pm

Hear's a really simply trick for checking wheel alignment, but it requires a fairly smooth surface.

Lay a length of paper down on the floor in front of the car. It needs to be a coupe of feet longer that the width of the car. Secure it with a couple of bits of tape at the ends. Newspaper (unprinted from a roll) is good, but thin wallpaper will probably do. Push the car over the paper. If the toe is a long way out the paper may tear, if not you should be able to get an idea of the toe from wrinkles, or the smears left by the tread as you get closer to zero toe.

The advantage of this method is that it takes some account of the play in the suspension joints.

A slightly more scientific method uses a pair of platforms that can slide sideways. You measure how far they move at the car is rolled across.
Paul

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

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geekygrilli
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Postby geekygrilli » Sun Aug 17, 2008 5:04 pm

Ooooo, I've not checked it yet, but...

My usual method involves a flat workshop floor, 2 x 10ft long straight edges, 4 x 5ltr paint tins, some packers and a tape measure (and a few iterations of changing, checking rolling back and forward). It has always comes out pretty well exactly where it needs to be. My MR2 and my brother's westfield were spot on when checked by laser alignment machines at MIRA - for castor, camber and toe :D

I would never ever let Kwikfit or the like anywhere near my cars. They're complete muppets and very rarely know what they are talking about...

Next week I'll set it to zero when loaded and see how it goes.


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