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Discussion Starter · #1 ·
I have found a simple way to measure and compare the rpm of slot motors;
I have employed a digital optical tacho, used with R/C planes; it is a cheap tool that costs today $ 19,99 at www.towerhobbies.com, but could be found in every modeler shop in U.K. and almost everywhere.
The probe was built with an old wheel, to which I have glued two strips of chrome tape, at 180° each other, protected with some nail clear polish.
To make the measure you must change one wheel of the car with the probe and run the motor at 12v, or at any other voltage with a regulated DC supply, and read the rpm under high light; of course you must multiply the reading for the gear ratio used. In the example the measure was 8800 and the gear 28/9 = 3,1; so the motor ( a Ninco NC5 ) was running at 8800 x 3,1 = 27300 rpm at 12v.
Remember to set the tacho for two blade propeller measurement, and use two strips of tape.
Obviously this measure is with no load, but useful to compare similar motors and choose the best of them.


The equipment used

The measurement
Ciao
 

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DT
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Cool, cheers sprint.

I was going to get one anyway for my planes. Helpful for tuning the motors.

Doesn't the KL test bench use something similar to this?
 

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If I could have located a suitable digtal tacho at the time, I wouldn't have bought the Kelvin Light Test Bench!
Why weren't you around when I needed you, Sprint?
Oh dear, this forum wasn't even around then!


The really HUGE annoyance withe KL Tester is that it requires you to stick reflective tape on each car's wheel to test its rpm.
Not much of a problem you may say.
Well, no it isn't, but it would be a ZERO problem if they had rigged the tacho to read the roller on which the driving wheels rotate. Then no messing with tiny bits of sticky tape would be required at all. Much much simpler.
 

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Testing at the wheel isn`t a true measure of the motor rpm is it? With the KL toy you can measure the wheels speed plus at the motor for accurate motor rev RPM. Bloomin expensive sander too
Does just about everyone know the Slot 32 story about selling the KL machine at the incorrectly converted price? Even Nic can laugh about it now
 

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Graham Windle
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I have a spanish made digital tacho which uses a magnet screwed on the motor shaft as a sensor, absolutly simple to use .
 

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Graham too!!!!!!
This is not good enough!
Why can't you guys tell me these things BEFORE I go blowing 200 quid on a high class sander?
 

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well their capacitors, as we have an unregulated supply it smooths out any ac spikes. simply

add big capacitor volts go up, power go up, car go faster


Rob.
 

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it's not working properly, the ecu isnt mapped properly yet... next on the dial is the turbo isnt boosting properly eh 3.9?


yeah not working properly.. YET!


I also think I need some new tyres as I'm not getting much grip atm
 

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Rich Dumas
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Most folks put the capacitors on the power supply rather than inside the cars. With the caps in the car there will be a very tiny delay as the caps charge when the voltage increases and a tiny bit more coast because the caps will discharge to the motor when the power is off. Having the caps in the car would be illegal in many places. As far as the tachometer goes I have always thought of them to be of rather limited value. You can tune up a motor so it really screams when it is free running only to have it bog down on the track. If you rig up a chassis dyno that puts a load on the motor you will learn a lot more. An experienced motor tuner can tell a lot from the amp draw as the voltage changes.
 

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Brian Ferguson
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QUOTE I'm not getting much grip atm

Some might argue that you lost your grip when you stuck all those caps in the car...


...just kidding.... maybe....
 

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yes but it's legal at ours and I bought the caps and it's my car so why the hell not? also the brakes were quite sharp so it's helped in that department

I also have a KL bench sooo.. a well

Fergy maybe so, but the tyres are only ninco rally things
I like living on the edge!
 

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Brian Ferguson
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Dan, I saw that too. They look the same and both have the same specifications, but the Hobbico unit is 5 dollars more.
They also have a GloBee unit, at $24.99 which has a couple more features.

These are all designed for outdoor use because indoor lighting can affect the reading - they are sensitive enough to register the cycle rate of electric lighting! In fact, that is how GloBee suggests that calibration can be verified. Might be best to use a battery-powered light source for indoor use.
 

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Al Schwartz
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And, of course, if you are using a well smoothed supply, adding caps to the car will add only weight, not power (NB "smoothed" and "regulated", while often associated, are not synonymous). There might be a slight delay in braking but it would be very short - doesn't take a long time to discharge a small cap into a dead short.

EM
 
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