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Old 03-20-2004, 01:53 AM   #1
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Default Measuring motor stats w/o a dyno?

I'm trying to get my stock p2k and monster all in tip-top shape for race purposes.

Problem is... I don't have a dyno, so I don't have any good way to determine scientifically if my motor prep has made any improvements.

I've got a 3.3v power supply and a multimeter, and I can see that my clean P2k draws somewhere around 5 amps unloaded (5.6 amps with a break in fan). Can I use changes in the current draw to infer anything about changes in motor performance?

Also, does anyone have any info on making a DIY rpm sensor? My multimeter has a frequency counter on it, and it seems like I could perhaps rig up an RPM sensor if I could find a proper hall-effect sensor (like used in integy's dyno)
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Old 03-20-2004, 02:11 AM   #2
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What you could do is get a motor and couple the shaft to the shaft of the motor you are testing, then run it up and see what voltage is produced from the slave motor. This wont give you the rpm, but a higher voltage will mean higher revs.

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Old 03-20-2004, 10:58 AM   #3
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Default Measuring motor stats w/o a dyno?

Torsion;

I have a Robitronic Dyno which I USED to use to test all of my Motors. Very good information, but my Buddies at the track have been using a much less scientific method with about equal success.

Take the Motor(s) you are considering/tuning and hook them up to a charged 6 cell pack for a few seconds. You will be able to easily hear any differences in Rpm and Accelleration from Motor to Motor. With a little experience, you will be able to tell which Motor is better. and which tuning changes made a difference.

Not very scientific, but it does work!
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Old 03-20-2004, 08:04 PM   #4
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Default Re: Measuring motor stats w/o a dyno?

Quote:
Originally posted by popsracer
Torsion;

I have a Robitronic Dyno which I USED to use to test all of my Motors. Very good information, but my Buddies at the track have been using a much less scientific method with about equal success.

Take the Motor(s) you are considering/tuning and hook them up to a charged 6 cell pack for a few seconds. You will be able to easily hear any differences in Rpm and Accelleration from Motor to Motor. With a little experience, you will be able to tell which Motor is better. and which tuning changes made a difference.

Not very scientific, but it does work!


and it works dam good too
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Old 03-20-2004, 09:35 PM   #5
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Ill third that
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Old 03-20-2004, 10:38 PM   #6
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What about current draw?

On Integy's web site the literature for the motor dyno says:

"a quick test for any 27T stock motor:set the output voltgae to 3.0V and a good stock motor should pull at least 8A"

Is this true? My unloaded stock motors are drawing like 5-6 amps, so does that mean they are out of tune? they certainly aren't the fastest on the track :/

If i tune them better, will they use more and more current?
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Old 03-20-2004, 10:43 PM   #7
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true? yes and no.

You can get a motor easilly to 8amps if it is not free (ie: too many washers or bushings tight... etc etc)
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Old 03-20-2004, 11:50 PM   #8
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Well, okay... sure a motor with a load on it (whether it's a fan, the drivetrain of the rc car, or an armature that resists turning) will draw more current.

but that doesn't really explain the integy comment. I don't believe that my 5.5 amp motors are running *better* than the motors that integy refers to.... so the implication is that a better-running motor will draw more current.

But maybe i'm barking up the wrong tree... don't know.
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Old 03-21-2004, 03:30 AM   #9
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A motor that draws less current yet still outputs the same RPM/Torque is much better...less heat, battery drain etc etc.

However, if two motors are as efficient as each other, then the motor that draws more current should theoretically be creating more torque and rpm.
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Old 03-21-2004, 04:31 AM   #10
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Generally speaking when the amp draw goes up so does your RPM's but down goes efficeincy. I've found when running a monster stock brush choice makes a huge difference in amp draw and overall power, this is also true of other stock motors.
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Old 03-21-2004, 02:06 PM   #11
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I have been thinking about this method: If I set an modelaeroplane prop on to my motor, and let the motor lay down on something that are connected to a weight ( then I see how strong the motor is ) and I will also try to read the RPM with tachometer ? Will I then have som good answers about my motors, if I compare them by doing this ?

Does you guys think this will work ?????


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Old 03-21-2004, 02:25 PM   #12
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Default Re: Re: Measuring motor stats w/o a dyno?

Quote:
Originally posted by mb racer


and it works dam good too
mb racer;

And who do you think taught me? You did!!

Guys;

In my testing of Stock Motors, I too was lured into the higher the amps the better the motor fallacy.
In fact, higher amps (within the same type Motor) only shows LESS efficiency, not more power.

Last edited by popsracer; 03-21-2004 at 02:33 PM.
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Old 03-21-2004, 04:40 PM   #13
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my new monsters draw 12 amps at 2 volts in most cases without loading


i believe the only way to find a fast motor is to track test it...ive used my dyno for years and i don't think it helps much unless you really know what your looking at

also one of the ways to get a really fast motor is to have your car setup up correctly (the less scrubbing of speed in the corners the better of course)

equalizing your batteries help too!!!!!
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Old 03-21-2004, 06:10 PM   #14
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Years?
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Old 03-21-2004, 07:46 PM   #15
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yes ottoman ive had a dyno a few years
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