# Adjustable brush advance.



## DIYguy (Sep 18, 2008)

mizlplix said:


> Yesterday, a guy came by in answer to my Craigslist ad for an old arc welder I had for sale. When he saw my car, he spent over an hour asking questions and sharing ideas with me. It seems that he is an Integrated System Engineer, (A specialist dealing with making pre-engineered components work together.)
> 
> One of those ideas was about the conveyor drive system They had at his work. It had a DC motor which used an adjustable brush timing, to minimize arcing and keep the motor running in an efficient mode.
> 
> ...


There has been a bit of tinkering with variable brush timing. I think the controlling of it is the key. There are a few threads on here about it. I think I may have started one.... ??? Denis Burube uses a small servo and drives his brush timing from near zero to (i think) 11 degrees, in the time it takes to get down the 1/4 mile. This is on a 13 inch motor in Smoke Screen. 
Apparently, there is about 2% torque per degree on the table. Of course if you have a transmission, you can get it back with the torque multiplication.... however, as you suggest, with direct drive (assuming your motor is large enough to begin with) it may give you what you need. 
Coming up with a servo or stepper that is tied to rpm is one idea. I really like the simple method like the old weights/springs in a distributor to mechanically advance the brush gear based on rpm. Now, if you could only design one that works well. 
I've thought of rigging up one with a simple pull cable... I'm sure it would more the gear ok....but getting the exact amount timed to the rpm would not be possible manually. It could give you some idea of potential though.

Jim Husted had a few pics of the sliding arrangement he came up with. Not sure if they are still on his site or not. 
Who is the manufacturer of the conveyor drive that has this system on it??


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## Salty9 (Jul 13, 2009)

Brush/commutator wear could be an issue. (I don't really know, just commented to get updates)


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## DIYguy (Sep 18, 2008)

Here is the thread I was thinking of.... and I didn't start it.... 

http://www.diyelectriccar.com/forums/showthread.php?t=49143&highlight=variable+brush+timing


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## sonicj (Mar 17, 2010)

i had this idea a few months ago when modifying the timing on my golf cart. what i had in mind was similar to the link above.... cut a new brushplate with slots that allow for adjustment and leave a tab on the plate that protrudes from the can, use something like a lawnmower throttle for on the fly adjustment. i think i drew something up... i'll have a look for it.
-sj


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## DIYguy (Sep 18, 2008)

I don't think the mechanical brush gear slide arrangement is the tough part. Its how to control the advancement in relation to RPM that's a bit more challenging.


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## sonicj (Mar 17, 2010)

i agree, automating the task would be the bidness. in the interim though, having the timing manually adjustable at the driver's seat is better than no timing adjust at all. 

for tuning the µC, could try mounting a small camera fixed on the com, record the position that gives the least arching at a given rpm, then plug those into a lookup table. OR maybe a photo detector inside the can to detect arching and drive the PID. 
-sj


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## albano (Jan 12, 2009)

sonicj said:


> i agree, automating the task would be the bidness. in the interim though, having the timing manually adjustable at the driver's seat is better than no timing adjust at all.
> 
> for tuning the µC, could try mounting a small camera fixed on the com, record the position that gives the least arching at a given rpm, then plug those into a lookup table. OR maybe a photo detector inside the can to detect arching and drive the PID.
> -sj


Put the vehicle on the dyno and adjust the timing.


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## DIYguy (Sep 18, 2008)

sonicj said:


> .... having the timing manually adjustable at the driver's seat is better than no timing adjust at all.
> 
> -sj


hmmmm, maybe not. You may have different thoughts if u screw it up a few times too many.


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## mizlplix (May 1, 2011)

I might be naive but I would put the vehicle on a chassis dyno where load, temperature and torque could be monitored.

A curve of advance/rpm/load could be worked up. 

I would also use an oscilloscope to monitor power anomalys, like brush arcing.

This would only need a small stepper motor and minimal CPU power to accomplish, once a reasonable curve was found.

Hey, look how devious a spark ignition curve is.....Static advance, Vacuum advance tapering off as rpm gains, Centrifugal advance gaining with RPM, and a high RPM retard to decrease emissions. (WHEW) Not to mention pressure retard if supercharged or nitrous is used.

It may be that the gains are not worth the cost, but what if they are?

Miz


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## sonicj (Mar 17, 2010)

DIYguy said:


> hmmmm, maybe not. You may have different thoughts if u screw it up a few times too many.


"Don't mess with that thing! You're gonna break it!" Thanks Mom! 

Seriously though, point taken. A costly new motor or your sole means of transportation probably isn't the best test bed for experimentation. Got it!



mizlplix said:


> It may be that the gains are not worth the cost, but what if they are?


on my golf cart, i gained approx 2mph by advancing the timing just a couple of °. might not seem like much, but when you have just one gear and your top speed is only 14, a couple MPH feels like a lot! i would like to advance it more, but i know i'll sacrifice a lot of torque... 

check this out  : 
http://www.youtube.com/watch?v=LYHZtl3Jq9g&feature=player_detailpage


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