# Rpm Limiting



## judebert (Apr 16, 2008)

I've been looking for a rev limiter to go with my 144V Curtis + ADC9" setup. I didn't buy the one at EVParts.com when I had the chance, and they've never had another whenever I went back.

I kinda like your idea. If you get something working, please let us know; I'm sure I won't be the only one interested!


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## jnissen (Apr 1, 2008)

Does the Curtis controller have that built in? I know on the Zen with an AC motor and Curtis controller they have a programmable field for the max RPM. Seeing this is a DC setup you may very well be stuck with a sensor and trying to feed this back.


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## judebert (Apr 16, 2008)

No, the Curtis doesn't have anything like that. I've purchased a Hall effect sensor and magnet collar for the ADC9" already. I'll be wiring it to the existing tachometer to provide a human-controlled rev limiter.

But that's fallible -- especially when I'm the human. I really want a solution that will allow me to loan the car to others. That would be a rev limiter.


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## dataman19 (Oct 7, 2009)

How about a tach based limiter?
I have read numerous articles and posts about how to get the OEM tach to work with the new electric motor.
And, as I remember, most drag racing and pro racing tachs have a rev limiter (IE Speed Governor) so just hack a speed sensor into the OEM tach circuit and use it for REV Limiting.
The secondary benefit is you will also have all the makings of a Cruise Control. All you will have to add is a speed sensor to pick up the speedometer (car speed) to give you a cruise control.
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Just thinking out loud...
..
dataman19


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## Dave Koller (Nov 15, 2008)

My tach pickup will go to an Arduino processor and have set points for keeping RPM's from killing my Motor by feeding resistive shunts across the throttle pot... Nothing fancy but I will stay tuned to this thread.. 
http://www.saturn.offical.net/node/326
(beating this to death - but will feed this signal as we did here both to tach and to processor ..)


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## dataman19 (Oct 7, 2009)

Dave Koller,
Excellent post.. But haven't I seen this info posted elsewhere..
..
None the less - you have a very good solution to several points...
...
dataman19


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## Dave Koller (Nov 15, 2008)

dataman19 said:


> Dave Koller,
> Excellent post.. But haven't I seen this info posted elsewhere..
> ..
> None the less - you have a very good solution to several points...
> ...


I work 80 hrs a week lol but I had that post on my
http://www.diyelectriccar.com/forums/showthread.php/getting-rid-pcm-saturn-30356.html

and when we first did it - along time back - lol 

I keep throwing things the above thread and will put in the processor in a month or so...


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## Homer (Aug 4, 2009)

Has anyone used this speed sensor for their motors?

Looks like it bolts right onto the tailshaft of a warp motor and can be hooked right up to a aftermarket tach.

http://www.rechargecar.com/product/warptm-speed-sensor


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## peggus (Feb 18, 2008)

I used a LM2907 f to V converter IC and a hall pickup. The circuit is in the datasheet.


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## dtbaker (Jan 5, 2008)

judebert said:


> No, the Curtis doesn't have anything like that. I've purchased a Hall effect sensor and magnet collar for the ADC9" already. I'll be wiring it to the existing tachometer to provide a human-controlled rev limiter.
> 
> But that's fallible -- especially when I'm the human. I really want a solution that will allow me to loan the car to others. That would be a rev limiter.



The rev limiter would only protect under load.... you still have the condition where a person may be coasting down a hill, and pick up speed past where they should shift. The motor wouldn't be under load so cutting the power would not help.

I just put little red stickers right on the speedo at each gear's 'redline' as a visual indicator.....


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## Woodsmith (Jun 5, 2008)

I am hoping to use the tacho to trigger a signal that will limit the revs on my motor. The standard MR2 limiter is set at about 7500rpm which I think is a fair bit too high so I will need to figure out how and what sets that and and what it does.

Maybe I can just put a micro switch on the dial face of the tacho and let the needle nudge it at the right speed!


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## Forklift Guy (Apr 20, 2009)

elevatorguy said:


> Has anyone done speed limiting to protect the motor?
> I had an idea, mostly stuff laying around, to create a speed sensor on the motor shaft, connect to programmable tachometer with shift light.
> The shift light would drive a relay to either decrease or cut off motor speed control input.
> I know some kind of hysteresis would need to be built to prevent bucking at limit or damage to controller may result.
> ...


 

I'm using a tach interphase module from Dakota Digital, which drives an aftermarket tach with a shift light. I use the shift light output to drive a relay, which opens my speed pot circuit. 

The only dissadvantage of this setup was that the Dakota Digital module uses a magnetic pickup. Their module requires a minimum of 34 teeth on a gear, for their pickup sensor.
This ment that i had to use my original Ford flywheel/ring gear, so my tach/rev limiter would work.


Brad
Forklift Guy


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## dataman19 (Oct 7, 2009)

First: dtbaker (Post #11 - this thread)..
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True a Tach Limiter only functions under load - if it is connected to an ICE Engine.
..
We are talking about an electric vehicle. Granted. I would suggest that one should put the Tachometer to monitor the motor speed (In fact this is what I do).
But - What stops you from putting a similar circuit on the drive shaft? In fact, what stops you from mounting two tachometer movements into one Tach Position. 1) to monitor motor speed, and 2) to monitor draie shaft (road) speed (actually, I think they call number two a speedometer - dah ohhh).
..
In NASCAR I believe they have a proposal to do just this.
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Since most modern cars use electronic speedometer drives, then it is just a matter of circuit wizardry to hook up a speed limiter (I think they already call these "cruise control").
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If you are prone to coast down long hills in neutral (a bad idea - especially since you are tossing away the benefits of regenerative braking - which would most likely give a far better range boost than coasting), you should consider a Tach and Speed Safety Sensor. Especially if you coast down hill and are worried about over-dragging the motor when re engaging the motor/drive train.
...
If nothing else a 9V battery, and three 2N3904 transistors will make up an and/or circuit. You know a circuit which only operates when there are two signals of a set amplitude (voltage), and or one is at a pre-set maximum.
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Simple circuit, just a non-typical application.
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I think they call this "Thinking Outside The Box". I call it "Mods without limits" - but then, once again, this is just my .75 cents worth.
..
Dave Mason


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## dtbaker (Jan 5, 2008)

dataman19 said:


> We are talking about an electric vehicle. Granted. I would suggest that one should put the Tachometer to monitor the motor speed


monitor speed it not the question... it is whether you can either make over-run blazingly obvious with flashing lights, or physically clamp down and slow things...



dataman19 said:


> ...just a matter of circuit wizardry to hook up a speed limiter (I think they already call these "cruise control").
> If you are prone to coast down long hills in neutral (a bad idea - especially since you are tossing away the benefits of regenerative braking


with and AC drive I would say, 'sure, engage regen when max rpm is exceeded'.... but with DC you are essentially in neutral with no braking unless you gain the attention of the driver. 

My only point is that circuitry to turn on an idiot light in that case may not be any more effective than a sticker on the speedo indicating what gear the car should be in......


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## dataman19 (Oct 7, 2009)

This is in response to ForkliftGuy - post #13-
..
If your tach requires 34 pulses per revolution - give it 34 pulses. A few CD4017's can be made to provide 34 pulses per pulse. The circuitry can also be modified to average the single sensor pulse and generate varying pulse speeds that are exactly 34 pulses (more like 33.9 to 34.6 pulses) per drive shaft pulse. You would only have to set the rev limits in a realistic range to allow for the sync (single Drive Shaft ) pulse to fall within a useable range.
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Then the timing circuit would generate a 34-pulse stream that would fall directly between the sync/reff pulse every time.
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Since the sync reference pulse spacing is varying by speed of the driveshaft (and you need exactly 34-pulses for each sync pulse) you would have to vary the frequency of the 34-Hz square Wave generator by a ratio of the sync speed.
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To complicate you math - it would be something like this...
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Say you have a vehicle that will do from 0-60MPH and the drive shaft will turn a maximum of 6,000 RPM at 60 MPH. You need 34 pulses per RPM - so you need a reference clock of 0-204,000 Hz. So if your reference pulses are 6,000 Hz - your clock will run a 204,000 Hz. Which happens to equate to 60 MPH.
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So if you are doing say 30 MPH your drive shaft will generate a 3,000 Hz reference clock which will trigger a 102,000 Hz clock speed.
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It's just simple logic and timing pulses (which are what makes a tach or timer work anyway). To ge honest, the circuitry would have to run at about 404,000 Hz and divide the output by two to give any real accuracy.
Such is the world o real time timing clocks, the higher the multiplier in the output clock the higher the accuracy.
..
But then, we aren't launching missiles at the moon? Or are we?
...
Dave Mason


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## elevatorguy (Jul 26, 2007)

elevatorguy said:


> Has anyone done speed limiting to protect the motor?
> I had an idea, mostly stuff laying around, to create a speed sensor on the motor shaft, connect to programmable tachometer with shift light.
> The shift light would drive a relay to either decrease or cut off motor speed control input.
> I know some kind of hysteresis would need to be built to prevent bucking at limit or damage to controller may result.
> ...


I just wanted to post a follow up, I used a optical sensor and a pulse wheel to feed a off the shelf tachometer with a programmable shift light. I used the shift light to drive a relay with a timer circuit to shut down the controller and main contactor for 2 seconds if overspeed detected.
I will use the light as well as an indicator.
This could be expanded for reduced throttle setup or multistage reduction or addition of a motor brake.
I also thought I can use the setting for a "valet" mode for other drivers not familiar with driving a EV.
I'm sure there are many ways to do this, this just seemed like a simple solution.


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## Dave Koller (Nov 15, 2008)

elevatorguy said:


> I just wanted to post a follow up, I used a optical sensor and a pulse wheel to feed a off the shelf tachometer with a programmable shift light. I used the shift light to drive a relay with a timer circuit to shut down the controller and main contactor for 2 seconds if overspeed detected.
> I will use the light as well as an indicator.
> This could be expanded for reduced throttle setup or multistage reduction or addition of a motor brake.
> I also thought I can use the setting for a "valet" mode for other drivers not familiar with driving a EV.
> I'm sure there are many ways to do this, this just seemed like a simple solution.


I posted more on my own pickup for ADC 9 at:

http://www.diyelectriccar.com/forums/showpost.php?p=151836&postcount=37

The output from the Cherry sensor will go to an embedded processor and read the RPMs ( it is buffered and sent direct to the tach also ) IF the RPMs reach a preset it will throttle back the Curtis via a D to A and not cut off the motor - just speed control it a bit ... Going downhill with no Regen is another story and I will let you know how the other device works later lol...


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## elevatorguy (Jul 26, 2007)

Dave Koller said:


> I posted more on my own pickup for ADC 9 at:
> 
> http://www.diyelectriccar.com/forums/showpost.php?p=151836&postcount=37
> 
> The output from the Cherry sensor will go to an embedded processor and read the RPMs ( it is buffered and sent direct to the tach also ) IF the RPMs reach a preset it will throttle back the Curtis via a D to A and not cut off the motor - just speed control it a bit ... Going downhill with no Regen is another story and I will let you know how the other device works later lol...


It looks good, a lot better than my quick pulse wheel made from a modified grinding wheel. 
Are you going to go multistage?, like reduction then zero throttle?
I am not using regen so that wasn't an issue.


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