# Variable brush timing!



## major (Apr 4, 2008)

Yabert said:


> Hi all
> 
> I have find a 11" motor you can see bellow. With his large brush, the 48 bobine in the rotor (same than ADC 9") and his armature of 5.75 in lenght it is very similar to Warp 11. Do you think it's a good motor at low cost to replace a Warp 11?


the 48 bobine in the rotor----What does this mean?

As far as Warp11, I don't know. But this one looks solid to me . Good find.



> So now I need to run it at hight voltage (120-150v). Probably advanced the brush by 10 degree to realign the flux will work.
> But what do you think about variable advance of the brush. Something like at 40v and low amperage the brush is set a 3 degree and when you snap the pedale to the floor the brush come at 10 degree. Maybe the brush holder can be variable from the accelerator pedale!
> Do you think it's a great advantage compare to a fix advance of the brush?


I think it is more trouble than it is worth. Set it and forget it.



> Also, in the case of this idea isn't good is it possible to add interpole to a standard motor to help it to run at higher voltage?


And who will design those interpoles and comm coils for you? Forgetaboutit 

Regards,

major


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## Woodsmith (Jun 5, 2008)

I've often wondered if variable brush advance would ever become the norm. 
I was thinking in the same way that, on ICE distributors, there used to be a manual advance on the steering wheel that was then automated as engines developed.


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## toddshotrods (Feb 10, 2009)

Woodsmith said:


> I've often wondered if variable brush advance would ever become the norm.
> I was thinking in the same way that, on ICE distributors, there used to be a manual advance on the steering wheel that was then automated as engines developed.


Me too - similar thoughts on this subject...


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## JRP3 (Mar 7, 2008)

major said:


> the 48 bobine in the rotor----What does this mean?


Comm segments?


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## major (Apr 4, 2008)

JRP3 said:


> Comm segments?


Then maybe 49


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## Yabert (Feb 7, 2010)

> I think it is more trouble than it is worth. Set it and forget it.


Hi
In fact isn’t that complex! It’s only to add a plastic rotary ring and two flexible conductors on the brush holder. 

With what I know at this moment, a fixe advance of the brush permitted at the motor to have more power because he runs at higher voltage but that reduce the low end torque. 
So with a motor fixe at X degree you need to put more Amp from stop to have the same acceleration than a neutral timed motor.
Personally I see a good advantage of efficiency to put 600 amps instead 700 to have the same acceleration from stop. 
Well I think than variable advance timing can always give the best efficiency from the motor because you can always have the best flux. The brush can always be at the better place to have the higher power and the lowest lost. Correct me if I’m wrong.

In fact what I need to know is how much low end torque a motor loses when his brush are fixe for high voltage (example: 8-10 degree for 120-150v)? It is 5%, 10%, 15%??


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## major (Apr 4, 2008)

Yabert said:


> In fact what I need to know is how much low end torque a motor loses when his brush are fixe for high voltage (example: 8-10 degree for 120-150v)? It is 5%, 10%, 15%??


Hi Yab,

Brush advance within reason has little effect on motor efficiency.

And I posted the reasons and logic before, so just the summary here. You lose about 2% torque for every 1° of advance for a 4 pole motor. 

Regards,

major


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## JRP3 (Mar 7, 2008)

So your typical 10+ degree advance is costing 20% or more in torque? That seems like a large enough amount that variable advance might be worth it.


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## toddshotrods (Feb 10, 2009)

JRP3 said:


> So your typical 10+ degree advance is costing 20% or more in torque? That seems like a large enough amount that variable advance might be worth it.


It definitely is for drag racing. It probably hasn't been a big concern yet because not many of the current racers seem to be fully utilizing the torque they have with the advance dialed in. I have a plan for a variable advance setup that I will probably use to help tune the launch to the track conditions. 20% is a nice amount of torque to be able to add/subtract as needed. I know the controller, especially a Soliton, can do this but having that last 20% of torque available in ideal conditions means lower numbers.


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## Woodsmith (Jun 5, 2008)

This is getting interesting even from the other end of the spectrum from drag racing.

If a small and efficient vehicle is losing torque due to brush advance for higher voltage and speed then it may need to use gear selection to regain that torque at the wheel for pulling away or hill climbing.

If the advance can be adjusted then perhaps that same vehicle could manage without selectable gears.

The efficiency of the motor may not be much one way or the other but not having a selection of transmission gears could reduce the weight and some mechanical losses by an appreciable amount.


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## Yabert (Feb 7, 2010)

Woooooh! Approximately 2% per 1°!!!! It’s a lot…..

I talk about efficiency because some motor set at 10 degree will need 720A instead 600A to pull the same car (in the first few sec. of acceleration) equipped with a neutral timed motor.
And more amps in the motor, the controller and from the battery reduce de efficiency.

So, like Woodsmith say, in a direct drive car, add 20% more torque at start for the same amperage is really significant.


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## Woodsmith (Jun 5, 2008)

This is prompting me to look at the BMW transmission on my trike.
If I bypassed it completely I could shorten the chassis and save a little weight.
The 9" motor I have has the brush boxes on a ring that can easily be rotated round on a lever or actuator.


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## JRP3 (Mar 7, 2008)

Yabert said:


> I talk about efficiency because some motor set at 10 degree will need 720A instead 600A to pull the same car (in the first few sec. of acceleration) equipped with a neutral timed motor.
> And more amps in the motor, the controller and from the battery reduce de efficiency.


In reality it's only for a few seconds, so unless you are constantly taking off hard from a stop I bet you'd notice no difference in overall efficiency.


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## Woodsmith (Jun 5, 2008)

JRP3 said:


> In reality it's only for a few seconds, so unless you are constantly taking off hard from a stop I bet you'd notice no difference in overall efficiency.


But would it make any 'driveability' difference and commutaton improvement in a direct drive vehicle that is doing some sustained slower urban driving with no advance and then some high speed driving with advance?


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## JRP3 (Mar 7, 2008)

Maybe?????


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## Yabert (Feb 7, 2010)

Hi

What do you think about this set up?

You can see the brush holder, the rotary ring (in green) and a kind of plastic bevel washer for maintain pressure (in white).

After that, you need two flexible wire at A1 and A2 terminals. So you need to connect one with 2/0 cable directly to battery and the other one need a loop to S1 or S2 terminals.

That seem to me correct....


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## Woodsmith (Jun 5, 2008)

Looks like it would work.
The cable connections could be the problem though as that size of cable won't be too flexible.

The set up on my 9" motor is like this.








The brush ring is the light coloured ring and it is held by a clamping ring in the centre.








This is the same with the clamping ring removed.
I could slightly loosen the clamp and rotate the brushes.

The cable routes from between the field coils and allows easy movement without to much cable bending.
I would still worry about fatigue if it is being moved at every press of the throttle though.

Maybe a long coil of cable that wraped loosely all the way around the brush ring would work. The few degrees of rotation would translate to much less movement of the cable overall. It would get in the way of brush removal though.


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## DawidvC (Feb 14, 2010)

The big DC motors at work use a similar setup for their brushgear. It is slotted to allow easy timing adjustment. If you allow enough movement on the brushgear you would be able to reverse easily with the motor. Have a look to see how White Zombie's setup work. I believe it is similar.

Dawid


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## Yabert (Feb 7, 2010)

Hi

Now I need your help. The desing of the rotary ring is good and I need some idea to move it.

With what I understand, I need to increase the angle when the voltage or the RPM increase.

So I can read the voltage from the controller or the RPM from some prox on motor. But I need an actuator or some other mecanical part to move the bruch holder?

Or maybe do you have any idea of some mécanisme (clutch or ??) I can put on the shaft to directly increase the angle when the rpm increase?

Any idea is welcome. Thanks.


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## JRP3 (Mar 7, 2008)

I suppose you could set it up mechanically connected to the throttle position with a lever or cable.


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## toddshotrods (Feb 10, 2009)

If you want an elegant, but moderately sophisticated, mechanical setup you need a small pump that can be driven off the motor shaft and power a hydraulic cylinder. The higher the rpm the more it's able to overcome a spring holding the brush ring at zero advance. With the right components, you would be able to tune the amount of advance with interchangeable orifices in the hydraulic system, spring rate, and pulley ratios driving the pump. Of course the cylinder would push/pull a lever or cable connected directly to the brush ring.

Personally, I want a full electronic system. Then the brush timing can be programmed just like ignition timing on an ICE.


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## Woodsmith (Jun 5, 2008)

That's a bit like the vacauum advance on an ICE distributor.

I think it can be as sinple as a mechanical connection to the throttle position or a fully programmable electronc solution.
But which will depend on which are the important parameters relating to brush advance.
If it is only motor speed then that can be controlled by the tacho. If it is the throttle setting then the throttle link, or voltage etc.

I still don't know what the controlling parameters are regarding advance so I can't help much more at this point other then to remain interested in the concept with half a foot still in the 'Why don't the experts do it.' camp.


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## toddshotrods (Feb 10, 2009)

I am thinking of the torque advantage of having zero advance at the stoplight/starting line. If you link it mechanically to the throttle you'll have more advance with a more aggressive take-off - the opposite of what's desired. The more aggressive you are off the line the longer you want that brush ring to hang around the zero advance position. That requires a control mechanism that's controlled by motor rpm.

I like the idea of using an rpm signal and some kind of electro-mechanical control systems best, but suggested an option for full mechanical control for the "carburetor" types.


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## Woodsmith (Jun 5, 2008)

The 'Heath Robinson' part of my mind is imagining a tacho dial mounted near the end of the motor with a bit of string tied to the end of the needle that pulls a spring loaded lever attached to the brush ring. As the rpm rises the brush ring advances. 

It has the advantage that the short needle relative to the long lever on the brush ring means that advance is not linear but starts slowly at low rpm and then advances quickly through the middle of the range and then slows again at the top end.

Now, how to do that electronically?


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## toddshotrods (Feb 10, 2009)

Woodsmith said:


> ...Now, how to do that electronically?


Stepper motor, with a control box that reads the tach signal.


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## JRP3 (Mar 7, 2008)

Advance needs to increase with voltage, we have a PWM signal from the controller that increases voltage to the motor, why not tap into that signal to control a linear actuator?


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## toddshotrods (Feb 10, 2009)

JRP3 said:


> Advance needs to increase with voltage, we have a PWM signal from the controller that increases voltage to the motor, why not tap into that signal to control a linear actuator?


That's fine with me. I just had rpm stuck in my head. I suggested a stepper motor though over the actuator because it's more precise. You have the option of being able to program it to go to "X" amount of total advance timing, and repeat that precisely and consistently as needed.


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## thetore6 (Mar 7, 2010)

http://www.youtube.com/watch?v=LYHZtl3Jq9g


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## Woodsmith (Jun 5, 2008)

thetore6 said:


> http://www.youtube.com/watch?v=LYHZtl3Jq9g


Interesting first post.

Your bike?

Have you any measurements of what the output is with and without advance and why manual and not auto advance?
Any more information about it?


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## toddshotrods (Feb 10, 2009)

Umm, to the moderators - I flagged that post because for some reason I saw a video about riding bikes in the snow. I thought it was a shameless ad - sorry guys.

The timing advance mechanism - now that I'm seeing the right video - is nice!


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## Woodsmith (Jun 5, 2008)

That's ok Todd.
I had to look twice, three times, to see that it was more then just zooming about on a bike to some music.

Still not sure about the *thetore6* but if he/she is genuine then hopefully there will be some more information.


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## DIYguy (Sep 18, 2008)

I'm interested in this subject also. Looks like you have a 11 GE motor there Yabert. Very similar to one I have in my EV ..only mine is a 9". I have my brush timing advanced 13 degrees. Thats a whopping 26% power opportunity. The truck already has gobs of power with the Soliton and AGM batteries. Those pics of slip rings for variable brush timing look like the ones from Jim Husted's site. I know he had intentions of selling the components to do this on various motors...as a kit. I should ask him what came of it. 

The way to drive this brush timing in the most efficent way is my current quandry.... Some interesting ideas so far!....


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## major (Apr 4, 2008)

DIYguy said:


> Thats a whopping 26% power opportunity.


Hey guy,

That is incorrect. The brush advance is similar to field weakening with regards to the effective flux. So less flux, less torque for a given current, but also greater RPM. Except for some minor loss difference, the power remains the same.

Using brush advance means you will get less torque from the motor than you would if the brushes were neutrally set. But there is basically no difference in the power from the motor at equal I & V inputs (advance vs neutral).

So all this additional torque these guys are seeing with neutral brushes on launch could be obtained with gearing. But then again, who uses shifting trannies? The real trick is how to and when to advance the brushes. And then not to have that mechanism cause adverse effects to the commutation. I see these levers which Jim has installed on motors like in the Zombie, but I don't see any control connected to them. And I think Bill used this on the Killacycle motors with a timed mechanism to push the advance forward. Not sure why I think that  So consider it a rumor 

Anyway, unless you're strictly a drag guy, I think it is more trouble than it's worth. But they're your motors and your projects....Don't blame me 

major


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## Yabert (Feb 7, 2010)

Thanks all for the ideas.
At this moment, the better way a can see to move the brush holder is a step motor actuator (picture) drive from the increase of voltage. 

Thanks also for your comment Major.
It's right a motor fix at 10 degree and one with variable brush have exactly the same power for the same Amps and Volts..... But at 10 degree only!!
The power is probably more like the graph. With variable timing the power go up constantly and with fix timing you lost 20% at the beginning and a bit to at the end.

You have reason when you said it's complex and that ''maybe'' is more trouble than it's worth, but in a direct drive application that seem to me logic to use.
Imagine, each start you do from stop is 800A instead 1000A to have the same torque. Or, in the other way, with a 11'' motor, it's 360 lbs-pi instead 300 lbs-pi of torque from start.

So, if I find a good and reliable principle to move the brush I will try it. If not, I probably fix the brush at 10 degree and forget about it...


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## Woodsmith (Jun 5, 2008)

A quick and easy way to find out is to have a manual control that can be easily adjusted on the move. Something a bit like the set up in that bike video above but maybe even simpler.

If it were me I would have the default position at the advanced position held with a spring.
Then I would experiment by holding the lever at neutral and then accelerating away and releasing it as I go.
If it accelerates better then I would make a better system with more investment.

Anyway, those with better resources and abilities may go straight into the electronic programmable route while I do 'Heath Robinson'.


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## DIYguy (Sep 18, 2008)

major said:


> Hey guy,
> 
> That is incorrect. The brush advance is similar to field weakening with regards to the effective flux. So less flux, less torque for a given current, but also greater RPM. Except for some minor loss difference, the power remains the same.
> 
> ...


Thanks Major... I appreciate your advise. I wondered how the drag guys were using this feature.......


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## mhud (Oct 19, 2009)

Hey DIYers, I hope you'll forgive my ignorance if I'm not in the ballpark. 

Say you were to install a stepper motor or a servo to dynamically alter the timing. Is the opposite force to the torque provided by the motor going to be transmitted through that mechanism? 

My understanding is that the brushes are mounted to the frame of the motor and the structure of the motor is what the productive torque reacts against. Is that right? 

If that's the case, you need to either have a pretty beefy system to adjust the timing while the motor is producing torque, or you need to cut power to the motor, adjust the timing quickly, then get it going again. 

My final thought on this path would be that while the motor is producing torque, the brushes will need to constantly resist being pushed back toward neutral/retarded timing.


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## Woodsmith (Jun 5, 2008)

The reactive torque of the motor is through the field windings into the frame and the frame will be anchored to the vehicle to resist the driving torque.

The brush ring is attached to the motor frame and so will not need to oppose any of the driving torque itself. Moving the brush ring will only require opposing the relatively small frictional forces between the brush and the comm bars, pushing the brushes towards neutral as you say, and any rigidity of the cables connected to it.


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## Matthijs (Jun 19, 2009)

I know there is a thread on the endless-sphere on the subject. Maybe members here can find some good info. 

http://www.endless-sphere.com/forum...&p=278427&hilit=Variable+brush+timing#p278427


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## DawidvC (Feb 14, 2010)

I had a quick look at endless sphere, but there does not seem to be anything concrete apart from some interesting theories. Using that nice actuator of a few posts ago, I believe something could be made to work. Any Arduino or PIC could run such an actuator, given the right set of inputs and a translation table. 

I believe we would need motor shaft speed, motor voltage and probably ( but not always ) the current being pulled by the motor. Translate that to a optimum position of the brushes via the lookup table and it should work.

Regards
Dawid


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## FlaJim (Dec 6, 2010)

What is needed is a viscous coupling. One side connected/riding on the rotor shaft and the other anchored to the brush ring. The coupling medium can be air or oil as needed to get the brush plate to move correctly. Then a simple spring system can be used to control the brush plate advance vs. rotor RPM. Changing the spring rate can be used to tailor the brush plate advance rate/curve. Put in a mechanical stop where you want the max advance to be.

No wires, no programming, and no pulling your hair out trying to build the perfect circuit to run it all on. As a bonus, your not using battery power to run another circuit/device.

Jim


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## Anaerin (Feb 4, 2009)

FlaJim said:


> No wires, no programming, and no pulling your hair out trying to build the perfect circuit to run it all on. As a bonus, your not using battery power to run another circuit/device.


No battery power used directly, instead you introduce drag on the motor to "power" the motion of the brushes, which means you have to use more battery power to turn the motor. So, no matter how you do it, you're pulling power from the battery. And a resistive-mechanical system like this will lag behind the RPM quite a bit, meaning it won't be able to move the brushes into place until it's well after the advance is needed, whereas an electro-mechanical will be able to pre-empt speed changes quicker.


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## DIYguy (Sep 18, 2008)

Dennis Burube uses a servo, time controlled starting close to zero on the line to about 12 degrees at the end of the 1/4 mile. Then, set back to neutral. According to Dennis it's " good at the track, but not on the street". 

By this I take it to mean a mechanism that self resets and can repeat the process as required for street driving... would be required.


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## toddshotrods (Feb 10, 2009)

Anaerin said:


> No battery power used directly, instead you introduce drag on the motor to "power" the motion of the brushes, which means you have to use more battery power to turn the motor. So, no matter how you do it, you're pulling power from the battery. And a resistive-mechanical system like this will lag behind the RPM quite a bit, meaning it won't be able to move the brushes into place until it's well after the advance is needed, whereas an electro-mechanical will be able to pre-empt speed changes quicker.


Plus, electronic control gives you the ability to make changes to the programming "on the fly". It would be nice to see series-DC technology reach the point EFI-ICE has, where you can plug in a laptop while driving down the road (or on the dyno) and fine-tune the whole setup for maximum power or efficiency form the keyboard.


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## DIYguy (Sep 18, 2008)

FlaJim said:


> What is needed is a viscous coupling. One side connected/riding on the rotor shaft and the other anchored to the brush ring. The coupling medium can be air or oil as needed to get the brush plate to move correctly. Then a simple spring system can be used to control the brush plate advance vs. rotor RPM. Changing the spring rate can be used to tailor the brush plate advance rate/curve. Put in a mechanical stop where you want the max advance to be.
> 
> Jim


Hi Jim, Interesting idea....have you found/seen a viscous coupling that would be suitable for this application? Also, I'm unclear how it is that you would mount this and "anchor" the driven side to the brush ring. Can you sketch something to help me understand your idea?

Thanks...


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## few2many (Jun 23, 2009)

Look at just about any simple 110v, single phase motor. It has a start and run circuit inside that is switched by a centrifical switch. When power is applied, the start and run windings are engaged. When the motor gets to a certain rpm, centrifical force throughs out a couple weights atttached to springs, which turns off the start circuit. Very simple and all adjustments made are the weights or spring tension.


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## DIYguy (Sep 18, 2008)

few2many said:


> Look at just about any simple 110v, single phase motor. It has a start and run circuit inside that is switched by a centrifical switch. When power is applied, the start and run windings are engaged. When the motor gets to a certain rpm, centrifical force throughs out a couple weights atttached to springs, which turns off the start circuit. Very simple and all adjustments made are the weights or spring tension.


Yes, this is the same way that the older ICE ignition timing worked. We use to change the weights and springs for racing.... . I wonder how to adapt the ones from electric motors to reliably drive the brush ring.... ?? hmmm..


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## few2many (Jun 23, 2009)

Someone mentioned doing it all electronically, nice idea in theory, but might as well with ac for all that!


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## peggus (Feb 18, 2008)

One way of creating a position feedback servo is to take a regular RC servo, for this application probably a jumbo servo intended for large sailboats. Remove the mechanical stop that prevents it from spinning freely, remove the internal position feedback pot. Couple the output shaft to the brush ring through suitable gear mechanism. Put a position feedback potentiometer (of the same resistance as the one you removed) on the brush ring and wire it into the servo control board. 

Controlling the servo is easily done with any micro-controller through a PWM signal. It's been done to death so no need to go into detail here.

Another way would be to take a off the shelf linear actuator with DC motor and wire it to an RC servo control board. Hmm, a window elevator motor and gearing would work well....

As always there are many ways of skinning this cat, the best solution depends on your particular skill-set. If you're most comfortable with steam power and mechanical governors, then go for it.

The real problem is finding the optimum brush position as a function of speed, voltage & current.


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## major (Apr 4, 2008)

peggus said:


> The real problem is finding the optimum brush position as a function of speed, voltage & current.


You got that right. I always figured you'd use a camera. Did you see jackbauer's video's of brush arcing with his compound motor? Cool.

But then I think, if you can do it with the eyeball, why not use a phototransistor (photocell, I guess) with an auto feedback loop to the servo and keep the light (arcs) to a minimum? Might be a mess of a PID loop to tune


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## peggus (Feb 18, 2008)

major said:


> You got that right. I always figured you'd use a camera. Did you see jackbauer's video's of brush arcing with his compound motor? Cool.
> 
> But then I think, if you can do it with the eyeball, why not use a phototransistor (photocell, I guess) with an auto feedback loop to the servo and keep the light (arcs) to a minimum? Might be a mess of a PID loop to tune


Yeah, I saw the fireworks, very exciting.

The photocell control would probably be something closer to a peak power tracking algorithm, chase back and forth to find the minimum.


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## few2many (Jun 23, 2009)

peggus said:


> If you're most comfortable with steam power and mechanical governors, then go for it.


 I happen to be a steam punk fan. Now youve got it! Steam Punk electric car!


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## peggus (Feb 18, 2008)

major said:


> Hi Yab,
> 
> Brush advance within reason has little effect on motor efficiency.
> 
> ...


Question for you Major:
In AC motors the Torque is proportional to the cross product of the stator flux density and the rotor flux density. So as you divert from 90 degrees the torque therefore weakens by the sine of the angle, not proportionally. Is it not the same in DC motors? And if not, Why not?

Thanks


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## major (Apr 4, 2008)

peggus said:


> Question for you Major:
> In AC motors the Torque is proportional to the cross product of the stator flux density and the rotor flux density. So as you divert from 90 degrees the torque therefore weakens by the sine of the angle, not proportionally. Is it not the same in DC motors? And if not, Why not?
> 
> Thanks


Hi peggus,

Yep, that is what I was attempting to say without the trig. But remember, on the 4 pole motor, work with electrical degrees.

major


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