# Direct drive Siamese motor go reverse



## Yabert (Feb 7, 2010)

Hi 

I start to think about siamese motor configuration direct drive to the rear differencial.

So I have a question...
Can I go in reverse with advance timing motor?
I know I need contactor for inversed the current, but is it posible without damage motor advance by 10 degree?

White zombie configuration!


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## TX_Dj (Jul 25, 2008)

Yes, you can set a siamese motor configuration to switch into reverse, you just need more contactors to do it. As with any advanced series DC configuration, you can make it run in reverse, you just don't want to apply a lot of amps to do it, so then going direct to the differential may not be conducive to such a desire, since it will take more amps to move the vehicle while stopped.

A transmission is a good thing, and if you want to go without, I'd recommend changing your differential ratio to something that gives you the best compromise between low-end torque and high-end top speed.


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## Yabert (Feb 7, 2010)

Hi

I think use a 3.64 rear differential ratio.
That give me approximately:

-1760 rpm @ 35 mph
-3030 rpm @ 60 mph
-4550 rpm @ 90 mph

For two industrial forklift motor it's will be ok. 

The real question about advanced timing motor in reverse is when I will start in reverse from stall there will be a lot of amps for 2-3 sec. There have chance to burn motor?

Thanks


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## TX_Dj (Jul 25, 2008)

Depends on how many amps you let it pull. Too much, you'll certainly get arcing. Too little, and you won't move. There must be a happy balance, I can't imagine that John Wayland pushes his car to back up.


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## toddshotrods (Feb 10, 2009)

People don't usually do power take-offs in reverse. You are usually pretty much creeping just to get enough clearance to go forward in the desired direction. That means you're probably not going to be drawing too much current, if your whole system is properly matched to the vehicle.

The White Zombie does indeed use a reversing contactor to back up. I am pretty sure that I remember reading that only one of the motors is used for reverse.


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## TX_Dj (Jul 25, 2008)

I've also seen something, I think it was on Jim Husted's site, where he's working to build an adjustable brush advancement for ADC-type series motors. As I recall, the reasoning for it was to allow the brush timing to be returned to neutral for reversing applications. Could also probably be a benefit for regen applications as well. (where's the popcorn icon? lol)


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## EVfun (Mar 14, 2010)

Yabert said:


> Hi
> 
> I think use a 3.64 rear differential ratio.
> That give me approximately:
> ...


Please don't do that unless each motor is considerably large than the Zombie motors or the vehicle is considerably lighter. Even the Zombie runs a 4.11 to one. The higher voltage (compared to a forklift) is going to raise the motors target rpm so you won't need to simulate a forklift's rpm range. For street duty I recommend even lower gears because running around the neighborhood at under 1500 rpm is going to be very hard on the motors. The motor voltage will be low, but the amps WAY greater than the battery amps.

As far as reverse goes, no problem to do it with contactors. 6 double pole contactors will get you series and parallel operation in forward and reverse just like shown in the Zilla manual (which can be downloaded for free.) You can do series and parallel forward and series only in reverse with only 4 double pole contactors. You have to limit motor voltage in reverse (which will tend to limit rpm) because the motors are timed for efficient forward operation. If you keep the applied voltage to less than half of what the motors can take going forward you should be fine (this is also why parallel motors in reverse isn't really needed.) 

The White Zombie uses a unique racing contactor system using a number of single pole normally open contactors. It only operates a single motor in reverse and the other one freewheels. This is not a good idea for a street car as it makes backing up a hill dicey.


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