# [DC Series] Race Motor Question



## Frank (Dec 6, 2008)

What is the impact of brush advance on motor torque at low speeds? The setup I'm using to drag race pulls like crazy at higher speeds but I wonder how much (if any) torque I'm leaving on the table at low speeds, ex. 0 -> 1500 rpm? I'm thinking about some kind of brush advance rig but wonder if it's worth it.

Thoughts and insight appreciated!

thanks,
Frank


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## major (Apr 4, 2008)

Frank said:


> What is the impact of brush advance on motor torque at low speeds? The setup I'm using to drag race pulls like crazy at higher speeds but I wonder how much (if any) torque I'm leaving on the table at low speeds, ex. 0 -> 1500 rpm? I'm thinking about some kind of brush advance rig but wonder if it's worth it.
> 
> Thoughts and insight appreciated!
> 
> ...


Hi Frank,

I've been through this a number of times. It's not exact, but not far off, IMHO. These are 4 pole motors. A shift of 180° mechanical (m) = 360° electrical (e). So an advance of 180°m would cause no difference. 90°m would reverse torque (and rotation). 45°m would net zero torque. So for an approximation, each m° = 2% torque loss. Maybe it isn't exactly linear, but I don't think it's that far off.

Hope that helps,

major


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## Frank (Dec 6, 2008)

Hi major,

Thanks, this is an interesting way to think of it. I'm using a nominal 11° advance so am likely experiencing a reduction of ~20% torque using this method of analysis. I've been assuming that at higher motor speed/voltage that everything is in the "sweet spot" which is why it runs so well. Given that I'm already at current limit this makes me think I should investigate further. I typically run the second half of the track in half the time it takes to do the first half (1/8-mile racing.)

It's been suggested that I return to 0° advance to see if the 60' improves but I don't want to mess with things too much mid season. Maybe reduced advance would net an improvement. If I had more amps I'd use them. Also, if I had a transmission it would make a huge difference in performance.


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## Karter2 (Nov 17, 2011)

Dyno test run ??


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## Frank (Dec 6, 2008)

I guess that would tell a story too...


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