Race Prepping Motors

6385 Views 16 Replies 9 Participants Last post by dkubus, Apr 22, 2020

mikejh

Discussion Starter · May 3, 2017

Hi All,

I am curious to know what is involved in race prepping series DC motors.

I have done a few searches and not found much so apologies if this has been raised before.

I see a lot of talk about the motors that are built by a few well known legends and a lot revolves around those motors having much higher torque than a standard motor.

If you take a standard Warp 9 for instance, what can be done to increase the torque?

My understanding is:

Increase armature diameter - not possible.
Decrease resistance to force it to draw more current and hence produce more torque. Don't they only have one turn on the armature to start with?
How can you decrease it any further?

I guess also, Kevlar banding to allow more RPM by preventing it from flying apart?

And the spray on gunk that prevents flashover in the CE? Can't remember the name of it.

And then special brushes.

How do the race guys put 2000A through them when I read other stories of motors being destroyed at 1000A?

Not saying I can do this myself or "it can't be that hard", just curious to know what more can be done to a fairly simple device.

Thanks.

Mike

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major

· #2 · May 3, 2017

Hi Mike,

Probably the best prep for any DC commutator motor is brush seating and commutator filming (aka. break-in). It's been discussed here numerous times. Maybe search for patina.

And no, not much besides more current to increase torque. Brushes back to neutral worth 5-10% but risk flashover (aka. Zorch).

major

Karter2

· #3 · May 4, 2017

With an ICE much of the "tuning" to increase power is done on the fuel supply/ carby/injection system.
The equivalent on a DC motor is the battery and controller to "feed" the motor what it needs to produce more power.
Batteries need to be carefully selected to suit the application (voltage, capacity, output ability) and the controller must be designed to "manage" the power supply efficiently to the motor.

Duncan

· #4 · May 4, 2017

Hi Mike

Major is the man for this but here is my tuppence worth

Your motor is designed for about 200 amps - at that current and about 1500rpm it will run all day and produce about 10hp
At that current the motor's temperature will be such that heat generated is being dissipated - it's temperature will not be rising

If you want more power then there will be more heat to dissipate
If you don't get rid of that heat then the motor temperature will rise until something happens

So you can increase the cooling with a blower - but this will have a limited effect

Basically you end up with a current/time

200 amps - Long time
400 amps - 10 minutes?
1000 amps - 1 minute?
2000 amps - 20 seconds?
(these are WAGs) - Wild Assed Guesses

The other side as Karter says is the battery/controller

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mikejh

Discussion Starter · #5 · May 4, 2017 (Edited)

Hi Guys,

Thanks for the replies. All makes sense.

I did read in one of my searches about the brush/comm break-in and was aware of the need to do that. Part of that thread was regarding the Evnetics guys zorching motors at 1000A but then it was apparent that they hadn't bedded the brushes fully which goes a long way to explaining the results.

I get the heat, and the need for the controller and battery to be up to the task, but they can only feed what the motor wants. Obviously you can't force current into a motor, only supply what it asks for. Unless of course you ramp up the voltage and force the motor to ask for more current.

Running a high voltage like 300V+ will cause the motor to draw more current but the brush/commutator interface would be seeing those 300V pulses even though the duty cycle say 50% would lower the averaged voltage to 150V. Am I right?
The inductance would resist a change in current, smoothing the PWM, but the voltage pulses would still be seen and I would think would stress the hell out of the brushes and comm?

I guess I am just wondering what is "special" about the custom motors that are built by Dennis Berube and Jim Husted, and how they might make motors that are superior to the standard Warp motors.
I guess like ICE's its the blueprinting and attention to every last detail that helps and a lot goes toward building a motor that is reliable under huge stress.

In another thread (ev power glide), Ev99saturn mentioned:

I'm running a single 11" GE motor that was custom built for drag racing by Dennis Berube. It replaced an 11" Warp HV that I went with originally. The Warp is a powerhouse for sure, but the Berube GE is in a league of it's own when it comes to torque and will lift the front tires off the ground on a hard launch.

The Warp 11 HV has the armature size of a Warp 9 due to the interpoles so I would think it would be slightly down on the torque of a normal 11" motor but I could be wrong here. I thought the reason for the HV was to be able to run a higher pack voltage without the arching and high RPM that it would cause on a normal non-interpolled motor?

But that would only account for a small difference in torque.

Im not disputing for a second that these motors are actually superior, just curious as to what makes these "race" motors so much better?

Mike

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piotrsko

· #6 · May 4, 2017

Controllers put out a square wave. So yes you are correct that the motor sees pack voltage. However with L/C in a circuit, the leading and trailing parts of the square wave get rounded off so the APPARENT voltage is much less. Current on the motor is a different matter. A voltage on effectively low resistance inductor makes huge currents until bemf equals the voltage applied.

Duncan

· #7 · May 5, 2017

Call me a cynical old sod but I'm not at all convinced about these "Race" motors
I think it is like "Blueprinting" - which is the least cost effective improvement possible
and is merely an excuse to take money off people

"Blueprinting" is from racing categories where you are not allowed to alter the engine at all and is meant to consist of selecting the standard unmodified parts that work best together
In practice is is machining the parts to the limits of the specifications of the standard parts - all of the parts in a "Blueprinted" engine should be inside the manufacturers tolerance
A way of getting a tiny bit of extra power by bending the rules

John Metric

· #8 · May 5, 2017

Glyptol. Motor varnish on every part not part of electrical path. or brush or brush contact points.
Helwig racing grade brushes
Extra turn on the brush spring

Couple pointers
After break in and After driving on the street for good long period pull motor and check runout again, if it went out of round, throw motor away
And start again.
Never stall your motor with a high amperage settings
Install a line lock
Don't run it far into back emf zone, shift before then.
Take lots of data.

Duncan

· #9 · May 5, 2017

Hi John

Don't run it far into back emf zone, shift before then.

Do you mean limit the revs? - or could you expand please

John Metric

· #10 · May 5, 2017

What I mean by too far is that your peak horsepower is made right at the rpm point where your motor current limit and your max motor voltage meet (assuming you have the battery to do it). Going higher in rpm is falling downward in power so shift. Also the back emf field keeps growing after this point and IMHO the trailing edge arc gets worse and worse.

electro wrks

· #11 · May 6, 2017

John Metric said:
Glyptol. Motor varnish on every part not part of electrical path. or brush or brush contact points.
Helwig racing grade brushes
Extra turn on the brush spring

Couple pointers
After break in and After driving on the street for good long period pull motor and check runout again, if it went out of round, throw motor away
And start again.
Never stall your motor with a high amperage settings
Install a line lock
Don't run it far into back emf zone, shift before then.
Take lots of data.

Dito on these points. You might find winding varnish (a generic term) with epoxy or other formulas that have a higher heat rating than Glyptol. There must be some info out there that has the best heat transfer rates of the various varnishes. This is a concern because what is sprayed on or dipped into the windings may insulate them thermally as well as electrically. The upside is that the windings mechanically shift around less and are protected from foreign materials when they're coated.

Rather than tossing a very expensive motor with a out-of-round comm, you might try re-pressing the mica, Bakelite, and/or insulated metal cones that lock the comm bars in place on the armature. This should probably be done under the supervision of a motor re-wind shop and the comm trued-up and the motor tried again. It could save some of the expense of having to replace a motor.

Duncan

· #12 · May 6, 2017

John Metric said:
What I mean by too far is that your peak horsepower is made right at the rpm point where your motor current limit and your max motor voltage meet (assuming you have the battery to do it). Going higher in rpm is falling downward in power so shift. Also the back emf field keeps growing after this point and IMHO the trailing edge arc gets worse and worse.

Thanks John - that makes sense

John Metric

· #13 · May 6, 2017

Well I actually meant to say throw out the armature. They are $500 for a warp9. But if the 1/4"X1/4" Copper comm bars could be reset somehow and then reground flat and round it might make sense.

electro wrks

· #14 · May 6, 2017

Here's a piece on banding comm segments for higher RPM use:http://iccinternational.com/blog/20...outboard-end-of-a-v-ring-comm-for-stability-1
BTW, what I called cones to hold the copper segments together are more properly called v-rings.

mikejh

Discussion Starter · #15 · May 18, 2017

Thanks Guys,

All good information and helping me to understand maybe theres not too much special about those motors...

John Metric said:
Glyptol. Motor varnish on every part not part of electrical path. or brush or brush contact points.
Helwig racing grade brushes
Extra turn on the brush spring

So John are you saying thats all you do to your race motors?

Mike

Frank

· #16 · Jul 27, 2017

The bit about Helwig "racing grade" brushes is important. You want H49 "red tops". And run that thing for a week on 12V to build a good comm film. Don't get greedy when you hit the track: start slow and keep letting the comm film build up. Never touch the brushes. Advancing brush timing raises the speed where max torque occurs but as Major points out, you give up some on the bottom. Some teams have rigged up brush advance systems but if you're bracket racing it's a lot of effort, so understand your goals. If you're pushing big amps, keep the motor cool between rounds. The best way is to pull air through the fan end but most folks push air through the comm end because it's a lot easier.

dkubus

· #17 · Apr 22, 2020

Seriously good thread to read through, and i love the part about pulling cooling air supply out from the fan end of the motors rather than pushing air in through the commutation end. Based on my limited experiments (bench testing only so far) with this I've found that "pulling" the air out from the motor actually cools better as the air is forced to "stretch or expand" rather than the opposite of being compressed into the motor when blown into the com end. Compressing the air reduces its cooling ability because of molecular friction (like turbocharged boost pressure in a heavily boosted ice vehicle needs an after cooler to help restore the air density due to compressive heating)... its still only theoretical for my current build (dual warp9) based race car but I'm optimistically looking to take this cooling strategy a step further by including cooling (heat exchangers) in the ducted supply side that is routed into the com end of the motor and drawn through from the fan end by an extremely strong vacuum producer (yet to be determined) thinking along the lines of positive displacement blower driven by a separate power source or not fitted to the vehicle at all and only used between runs ?? Anyway if anyone has some theories they'd like to share id be keen to hear them. Refrigeration based, dry ice chilled fluid cooling etc lots of ideas, some probably worthwhile some probably not?

My application is tarmac hillclimb so its not quite like drag racing where you might apply full power for the full run however my run times are more like 50-65 seconds rather than 5-12 seconds for speedy quarter mile runs. Hillclimb run consists of steep grades and fast straights segmented by corners, crests and various other forms of restrictions that mean you're never on full throttle for the entire time. Still i envisage that the thermal loading will be much greater than a typical drag racer might experience in a quarter mile run?...

For this reason I'm more than willing to throw quite a lot of additional complexity and power resources into cooling system or at least interval-cooling as i typically get an hour or so between runs up the mountain.

Hope you're all staying safe and well.
Cheers guys.

Mike.

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