Burnouts in an electric drag car

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EV2Go
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Burnouts in an electric drag car

Post by EV2Go » Tue, 08 Mar 2011, 19:50

Just wondering when EVs evolve to insane power levels, how are we going to control high RPM burnouts?

Here the thinking, electric motors need load to control revs, (don't believe me put your EV in neutral and put your foot flat to the floor - DC anyway can't say for certain AC).

There is no fuel to cut, no spark plugs to drop random cylinders, and no timing to retard.

When we start to produce the kind of torque / power that will just bag the tyres like a top fueler, what is going to apply the load to the motor when it spins the tyres so freely?

Only way I can see this working is to use an RPM sensor and cut either voltage / amps or both to the motor (assuming the function was built into the controller), but will the controller be able to react fast enough?

Or will we see an aftermarket industry emerge like MSD etc to control additional functions?

Some may think... thats simple copntroller like the Soliton 1 already have a Kw limiting function built in whereby it reduces the volts / amps to stop the power going above that limit, regardless of what amps you dial in.

But I am willing to bet that will only work in a fully loaded situation crossing the finish line.

But in a drag application you will need plenty of oomph to get the wheels turning in the first place to warm the tyres, and then some way of backing off the power quickly to stop an over rev, but not so much that it stops the burnout.

The other thing is motors don't have things like rocker stoppers to guard against accidental over revs, so how do you reach this optimum burnout without trashing a few motors in the process?
Last edited by EV2Go on Tue, 08 Mar 2011, 08:54, edited 1 time in total.

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Burnouts in an electric drag car

Post by Tritium_James » Tue, 08 Mar 2011, 20:23

You run either an AC motor, or a DC motor with a speed sensor of some sort and a controller that's smart enough to use it.

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Burnouts in an electric drag car

Post by EV2Go » Tue, 08 Mar 2011, 20:33

In order for it to be smart enough / safe, it would have to be able to handle a instant WOT free rev without over reving and exploding the motor, is there an AC or DC controller that smart already?
Last edited by EV2Go on Tue, 08 Mar 2011, 09:35, edited 1 time in total.

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Burnouts in an electric drag car

Post by Richo » Tue, 08 Mar 2011, 20:35

traction control...
So the short answer is NO but the long answer is YES.
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Post by Johny » Tue, 08 Mar 2011, 20:36

AC is intrinsically safe to over-revving as the controller is totally in charge of turning the rotor - degree by degree.

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Post by Speedily » Tue, 08 Mar 2011, 20:37

EV2Go wrote:

The other thing is motors don't have things like rocker stoppers to guard against accidental over revs, so how do you reach this optimum burnout without trashing a few motors in the process?
Good planning and it would help to be god like lol

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Post by EV2Go » Tue, 08 Mar 2011, 20:37

Richo wrote: traction control...


which is just a means of limiting the power, in drag racing you need to buzz the tyres to get heat but not rev it so hard that it explodes.

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Burnouts in an electric drag car

Post by EV2Go » Tue, 08 Mar 2011, 20:39

Johny wrote: AC is intrinsically safe to over-revving as the controller is totally in charge of turning the rotor - degree by degree.
Does this mean the future of drag racing is AC?

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Post by EV2Go » Tue, 08 Mar 2011, 20:40

Speedily wrote:
EV2Go wrote:

The other thing is motors don't have things like rocker stoppers to guard against accidental over revs, so how do you reach this optimum burnout without trashing a few motors in the process?
Good planning and it would help to be god like lol
Failing my God like abilities... maybe a block of wood under the pedal Image

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Post by Speedily » Tue, 08 Mar 2011, 21:06

EV2Go wrote:
Speedily wrote:
EV2Go wrote:

The other thing is motors don't have things like rocker stoppers to guard against accidental over revs, so how do you reach this optimum burnout without trashing a few motors in the process?
Good planning and it would help to be god like lol
Failing my God like abilities... maybe a block of wood under the pedal Image


or a centrifugal clutch setup as a brake

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Post by EV2Go » Tue, 08 Mar 2011, 21:10

Not very energy efficient but the idea has merrit. The higher the revs go the higher the clamping force that is applied, much like a dyno really.

Hmmm maybe a generator that could be loaded up to return power back to the pack?
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Post by Speedily » Tue, 08 Mar 2011, 21:22

I though the idea was to stop over rev not work on the thermodynamic of free energy :)

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Post by Electrocycle » Tue, 08 Mar 2011, 21:52

it's very simple to add a module that monitors the rpm and either connects to an input on the controller to cut the power, or could actually adjust the throttle signal to maintain peak rpm under varying loads if necessary.
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Post by EClubman » Tue, 08 Mar 2011, 22:46

I don't understand the problem.
Big drag-worthy DC controllers have an rpm input.
My Zilla quite effectively limits my motor's rpm with a wide open throttle.

Mark

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Post by Speedily » Tue, 08 Mar 2011, 23:44

EClubman wrote: I don't understand the problem.
Big drag-worthy DC controllers have an rpm input.
My Zilla quite effectively limits my motor's rpm with a wide open throttle.

Mark
Electrocycle wrote: it's very simple to add a module that monitors the rpm and either connects to an input on the controller to cut the power, or could actually adjust the throttle signal to maintain peak rpm under varying loads if necessary.


yes i think Paul was look at it as a IF the motor can go 0 rpm to 10,000 in 1/100 sec how will we stop over rev   

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Post by Electrocycle » Wed, 09 Mar 2011, 00:56

you need a fast rpm monitor :P

The motor won't keep accelerating if it's not getting power!
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Burnouts in an electric drag car

Post by EV2Go » Wed, 09 Mar 2011, 03:32

EClubman wrote: I don't understand the problem.
Big drag-worthy DC controllers have an rpm input.
My Zilla quite effectively limits my motor's rpm with a wide open throttle.
Mark

Yes but how many much smoke was coming off the tyres at the time? I don't have concerns over my Soliton 1 controlling over all power either, but it is the instantanous free rev that scares me.
Electrocycle wrote: it's very simple to add a module that monitors the rpm and either connects to an input on the controller to cut the power, or could actually adjust the throttle signal to maintain peak rpm under varying loads if necessary.

I think this is more likely to be the answer, some way of recognising it is heading for destruction.

Something like... (pseudo)
If 4000rpm to 5000rpm =< than .1 sec then throttle = 90%
If 5000rpm to 6000rpm =< than .1 sec then throttle = 70%
If 6000rpm to 7000rpm =< than .1 sec then throttle = 40%
If 7000rpm to 8000rpm =< than .1 sec then throttle = 0%

Edit: Whoops forgot to restore power if it takes longer than .1 sec

ElseIf throttle = 100%

and some kind of RPM limit.
Last edited by EV2Go on Tue, 08 Mar 2011, 16:40, edited 1 time in total.

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Post by EV2Go » Wed, 09 Mar 2011, 03:51

So the way I see it working is have the throttle wires as an input to sense actual throttle position, have the RPM sensor as another input, some kind of time clock or timed clock cycles, a very simple loop routine and a throttle output, either as a raw signal or modified.

Obviously you wouldn't want the throttle position out to ever be higher than the raw input in, or modified output, but that would be easy enough.
Last edited by EV2Go on Tue, 08 Mar 2011, 16:53, edited 1 time in total.

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Post by coulomb » Wed, 09 Mar 2011, 04:05

Electrocycle wrote: you need a fast rpm monitor :P

Well, exactly, fast. Also the controller needs to react to the RPM input very fast. It's no good if it only checks the RPM input every 0.1 seconds, and the RPM has gone from 4000 one sample to 14,000 the next.

I have no idea how fast a series motor can over-speed at low load, but I can imagine a simple RPM limit circuit that reacts too late or too slowly to save the motor.

I think that burnouts, where the wheel is spinning pretty fast and generating a lot of smoke, is actually a moderate load on the motor (the energy for that smoke comes from the motor, obviously). So the danger may not be so much the burnout as the accidental wide open "throttle" in neutral, or in a direct drive vehicle some sort of break in the transmission (e.g. tailshaft bolts sheer off).

This seems to be a hazard unique to series DC motors, although I wonder what would happen to a sepex or shunt motor that lost field. You could lose the controller (if not well protected) and motor in one event   Image
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Post by EV2Go » Wed, 09 Mar 2011, 04:16

No definately wouldn't want to sample that slow, you would want to sample as fast as possible to catch it early.

I was only using a 1000rpm variance over .1 sec as a psuedo reference point. Probably want it to measure every pass through the loop for variation.

So if it was sampling a 1000 times a second you might want to say something like.

If NewNumber => OldNumber + 20rpm then Throttle = Current Throttle - 10%
Else If Current Throttle = 100%
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Post by EV2Go » Wed, 09 Mar 2011, 19:18

Thought just crossed my mind on this... using my motor as an example it creates peak torque between 0 and 2500rpm. If we are trying to break traction (which is the whole purpose of the burnout) we would ideally want to keep the motor in the peak torque range.

I wonder if some kind of two step could be built into the controller or seperate box?

Using one of the analog / digital inputs with a momentary switch, you could do the burn out maintaining 2500rpm, then after the burnout let go of it and stage with full revs available.
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Burnouts in an electric drag car

Post by Richo » Wed, 09 Mar 2011, 20:49

EV2Go wrote:Does this mean the future of drag racing is AC?


Yep Image

See DC has a real problem of uncontrollably over revving... Image
So the short answer is NO but the long answer is YES.
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Post by Thalass » Thu, 10 Mar 2011, 05:12

I'm fairly certain the Cougar open source controller could probably do this. And the AC version probably would, too.
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Post by EV2Go » Wed, 30 Mar 2011, 02:05

Martin from EVNetics just got back to me with regards to a question I asked about the Soliton catching an over rev, while he said it didn't catch it perfectly this video link he sent shows the motor is still in one piece.

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Post by rjws » Sun, 19 Jun 2011, 17:05

If you have an electronic controller, you might use a simple, outboard, electronic circuit with a couple of cheap op amps to modify the 0 to 5volt output of the throttle pot/hall effect sensor so as to allow any one of a number of selectable ramp times. The modifying voltage would be the RPM output of the controller or a similar signal derived from a wheel RPM monitor (again, a simple electronic circuit). You could then select "Burn Out", "Win Race", "Road Warrior", "Grandma" or "Shopping" etc.

The total cost of something like that is a few dollars, at most, and the response time, being analogue, can be as fast as you want it to be. No 'digital delay' at all. It is simply a form of analogue cruise control that will limit either the maximum RPM of the wheels or it will ameliorate the rate of RPM increase of the wheels.

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