# Advanced brush timing with electrical reverse?



## EVfun (Mar 14, 2010)

Keep the peak motor voltage in reverse low and the motor current reasonable and it should be fine. You might run a little less than 12 degrees advance unless that motor really needs that much to run at 150 volts.


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## major (Apr 4, 2008)

Hi wb9k,

An 11" in that truck? I wonder if it will hold up. I mean the truck, not the motor.

You have to remember that on a 4 pole motor, each mechanical degree (°m) is equal to 2°e (electrical degrees). 360°e gets you back to where you started. 180°e gets you negative torque (reverse motor rotation). 90°e gets you to zero torque. That is an advance (or retardation) of 45°m from brush neutral will result in zero torque production. 

So that 12°m advance on your motor results in about 25% loss of torque/amp. Why do that? The edrag racers loading to a couple thousand of Amps need it to successfully commutate. But I doubt you need or could stand that level of motor output.

You are correct the advance becomes retardation when you reverse the motor. This becomes a problem to the edrag racers. White Zombie blew (zorched) one of its motors reversing up a hill. It is hard to get around. That and the fact that motor reversing requires a pair of large contactors, is a big reason a lot of guys stay with the reverse gear in the tranny.

I don't see a good reason you would use 12°. I think you should back off to 5 to 7°m and limit current and speed in reverse if you can. That will significantly lower the chance of a zorch backing up an incline or rocking out of a snow drift.

Regards,

major


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## wb9k (Apr 9, 2015)

Thanks for the replies. Major, I assume you're the same Major from ES....

The motor is a tad overkill, but I want it to last and be able to maintain/accelerate to 55 mph going up a hill. I'm not looking to set any speed records or smoke the tires. We're going to use the original driveshaft (it will need to be lengthened a bit) and rear end....driving the motor hard would just shred the rest of the drivetrain. So there will be some limits on acceleration in both directions. Sounds like heavy timing advance is really only needed with sudden bursts of big power? Reading the sticky on picking a forklift motor, it sounds more like a flat out requirement...is that because guys are using smaller motors most times and therefore will need to drive them closer to their limits to drive even a fairly small car?

My driveway is a bit of a climb out to the street. In the wintertime, getting out requires some finesse, but not a lot of power, really. I will probably need chains on the rear tires in the winter. 

Extra contactors is something I have piles of, so two more to make reverse possible is no big deal. The slight increase in electrical losses is more than offset by the ditching of the tranny, IMO. 

My dad and I got new motor mounts almost done. I'll get some pics up and into the ES thread. Now I need to get a controller picked. There's a Raptor 600 on eBay that looks OK. I'd like to keep it under $1k for the controller. 

Thanks again for the input.

dh


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## Yabert (Feb 7, 2010)

I like your direct drive little truck project. 
As controller, you can maybe look at the Zeva 600 Amps controller at around 900 US (1195$ AU).


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