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Cut two tyre shaped holes in the top of a crystal Slot Car box. Mount a throwaway chassis and axels with motor underneath so that the wheels just poke through the holes. Wire up the motor to a digital voltmeter, and wire up a 12v power supply to two strips of copper/foil at the front, either side of a small guide split. Your car takes power from the copper and wheels turn the 'rollers' (old chassis wheels) which turns the motor which gives out a voltage, which is displayed on the voltmeter. Hope this helps, because it is a really simple yet extremely effective solution to the "how fast is my car" question. Unfortunatly, it won't measure torque/acceleration, but you can test the car under load by leaning something against the rollers.

Lotus
 

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I'm being rellay thick now Lotus. I've just read your post for a dyno and whilst it is an elegant and cheap piece of kit, how is it useful? Yes a voltage is generated, but what can you do with that? I suppose you could put all your cars on it to compare generated voltages.... OH! I think I see the light (not a train in the tunnel!). The faster a car's wheels rotate the higher the voltage
Then again, wouldn't a track session determine the faster motor?

I'm not trying to condemn your gadget, I like gadgets, I'm just a little confused...


Mark.
 

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You're right, the higher the voltage produced the faster the motor spun. This would indicate peak HP & torque potential. It is also limited to being a comparison type tester as it is not definitive nor comparable to anyone elses rig. It isn't great but it isn't bad either since it at least lets you compare before and after work you've done to a motor or compare other motors to each other. You just need to remember that the results from your findings are only able to be directly compared to other motors on the same rig.

For those of us that don't have home tracks this sort of testing at least gives us an idea of what to expect from our motor. Even if you have a home track, this simple test will let you know in advance if you're ready to reassemble the car or not


For the tests that I ran on this style 'dyno' I liked to use a heavy motor directly coupled to the motor being tested. You can also test acceleration capabilities of gear ratios you intend to use on your car by tieing into the rear axle instead. You still need to track test but at least you get an idea of whether or not you're headed in the right direction before you can get to the track.
 

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Russell Sheldon
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I agree with you a Bill. Nothing like controlled bench testing to improve a cars performance. Its amazing just how much extra speed can be found by just fiddling with the brush spring tension, for example. Not much good with sealed motors, though!

I believe the Wright Way dyno is nothing more than described by lotus03. In fact, the slave motor is a Parma 16D mounted to an inverted Parma Womp chassis with the tyres sticking through the cuts in the top of the box -- not exactly a sophisticated piece of equipment!

I'd be keen on the Kelvin Light dyno is it could measure amp draw up to around 10 amps. Not much good for me as it is, especially at the price being charged.

With kind regards

Russell
 

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Beppe Giannini
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Without spending 1,000 Euros for a Robitronic test bench (which would probably need to be modified down from RC motors) - one could use Lotus 03's elegant set-up with a sidewinder bottom chassis, connect a variable resistor to the "brake" motor and measure the torque on the sidewinder cradle with a small scale

Or, maintain the arrangement as it is (but still with the variable resistor) and put the scale under the car's guide - as you lower the resistance, the speed goes down, the torque increases and the weight on the guide decreases

OK, you also need to measure current, speed and have a stabilized voltage

Beppe
 

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If you want something which will tell you real RPM, then go to a model airplane shop and ask for a Tachometer. They put a bit of foil on the blades and spin it up in front of the Tacho, and it tells you the RPM. Some have adjustments for 2-3 blades, so either put two bits of foil on your wheels or multiply your reading by 2.

Simple, they cast about £20-30 I think. Otherwise you are talking big money for something like that.

Track time is good and ultimatly better than benching, but its not always possible to do it on the track you race on. And testing on a different track is not worth it.

Lotus
 

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Hi

Local group uses a "dyno" as a cheap test for cheating in stock class cars! No need to disassemble and check the gears or open the motor for "improvements", they use a simple car and if the reading is outside of a given range of tested "legal" cars, then the thing is dismissed. Takes a second.
the easiest way to do this is to buy the Tamiya box that people use for their "run ina trough" tracks. Reads in Km. Remove the front rollers and stop, cut a slot, add contacts and hook up power. Tells instantly if someone has "relabled" a stock motor or popped on that 10 tooth pinion.

Fate
 

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QUOTE (McLaren @ 17 Mar 2004, 20:12) <{POST_SNAPBACK}>If you want something which will tell you real RPM, then go to a model airplane shop and ask for a Tachometer. They put a bit of foil on the blades and spin it up in front of the Tacho, and it tells you the RPM.

I got a new tachometer for 30 euros (41 USD), and it has been extremely useful. For example, it tells when a motor zapped with neo magnets has reached its full potential. Measuring the RPM of rear tyres tells a lot about the transmission: replacing a badly worn Scalextric FJ gear & pinion with good ones added 3000 rpm.
 

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A quick and cheap mod to the dyno lotus decribed would be to add an amp meter in series with the circuit.

The more volts will indicate a higher speed motor but with an amp meter in the circuit you can see if a motor draws more current for the same revs (voltage) etc.

Also if a motor is on its way out sometimes they draw alot more current (amps) so it could be useful to spot half knackered motors.
 
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