Volts Vs Amps

[multiracer]

Test question.... Given a dozen group 12 motors, all with simular magnets, air gap, intruder style blanks, same springs and brushes, same surrounding metal can, armatures from different manufactures.
With a regulated power supply set at say 6.0 volts, reading the amps for each.
Set the power supply at 9.0 volts and read the amps again.
With this data in hand... what is the theory of volts vs. amps testing motors out of the car. Is more amp suck better? or is less? or do they both have merits?
I am searching for a way to get a feel for the performance of a given motor before it goes on the track for the acid test.
Thank You

[HurricaneLarry]

Unfortunately it would be easier to use one of those items to get your results closer, but we all know they do not work, or do they?

There are way to many variables that effect the performance of each motors, I suggest K.I.S.S, Keep It Simple Stupid. No pun intended. The best way it to approach this is simply build your motors the way most everyone else has been building them and work forward from there. No power supply can tell you how a motor is going to react under load conditions on any track. If that where the case, racing would not be so much fun and frankly I enjoy the building aspect of the whole hobby. And if you win it makes it all the more enjoyable.

High amps when building Boxstock motors would only denote a problem with the motor. Most BS motors will run on 5 volts at about 2.5-4.0 amps and to narrow it down any further would be a great accomplishment and a well sought secrete by many of us, so if you find something more please share it.

I have been building motors a long long time and have made many mistakes which in fact have made me a better builder if there is a science to it I have come close to finding it but still have not. I would say the science is in the systematic building of many motors combined with the selection of many different combinations of Magnets, Cans, Brushes, springs, and Arms.

All this is controlled by the track you run on and the power they have to offer the motor. Every motor will run different on every track. I have seen it more times then would like too, you spend hours building your fasted motors only to find out when they hit the track it runs like Dog. So where is the science in anything? My approach is simple, I find something that has potential and go from there, making subtle changes from one extreme to the other and compare my results, finding something that improves what I already know works will drive and has driven me and many others NUTS.

Good luck in your quest for a scientific approach.



PS: I also build motors for other racers too. If you need me you can email me.

[Tom Marsteller]

Usually when I build up a motor, I watch the current draw after the brushes are properly seated. Usually at 3 volts my motors are closed to peaked out current wise (can motors). After 3 volts and up to 6 volts my motors may climb milliamps in current and above that with light tension springs the current slowly begings to drop. This I think is due to the brushes floating off of the comm and because of the decreased dwell time on each segment. A strong group 12 motor I build up for scale racing will usually draw between 4 to 5 amps at 3 volts dependant on timing.

Tom......

[pbj59]

When you guys test a a motor, do you have it under a load or just free? Since the car is running approx. 12-14v on a commercial track under a load ( try to estimate weight ,drag and gearing - momentum ) would that be the best indicator of how it will do?

[multiracer]

All right....
If a " no load" situation does little to understand possible performance.... then what do we need for a miniature chassis dyno?
Thanks

[Tropi]

A dynamometer doesn't test "free running".
It applies a load, preferably variable loads. If it can't apply a load then it is not a dynamometer! :)

[multiracer]

This is correct.... Now, read the post's again!

[Slik]

Originally posted by multiracer
All right....
If a " no load" situation does little to understand possible performance.... then what do we need for a miniature chassis dyno?
Thanks

Just to measure RPM's? Hmmmm.... sounds cool :)

[cheater]

Originally posted by multiracer
All right....
If a " no load" situation does little to understand possible performance.... then what do we need for a miniature chassis dyno?
Thanks

You need a load on the motor that closely approximates the load it "sees" when trying to accelerate a slot car down the track.

Unfortunately, that is only half of the problem. You also need a power source that simulates the power furnished by the track.

IMO the first condition is possible to simulate.

The second condition seems to me to be almost impossible to simulate, given the variability in power sources and wiring between different tracks. In response to Tropi, this is where I see the most variance occurring: in the power supplied by the tracks, not in the load seen by the motor.

Which brings us back to reality: on-track testing is likely to remain the best way to go.

[cheater]

Originally posted by multiracer
All right....
If a " no load" situation does little to understand possible performance.... then what do we need for a miniature chassis dyno?
Thanks

You need a load on the motor that closely approximates the load it "sees" when trying to accelerate a slot car down the track.

Unfortunately, that is only half of the problem. You also need a power source that simulates the power furnished by the track.

IMO the first condition is possible to simulate.

The second condition seems to me to be almost impossible to simulate, given the variability in power sources and wiring between different tracks. In response to Tropi, this is where I see the most variance occurring: in the power supplied by the tracks, not in the load seen by the motor.

Which brings us back to reality: on-track testing is likely to remain the best way to go.

[RocketRod]

Whereas a dyno would be helpful is seeing the amp draw with a load applied, it doesn't tell how loads are applied to the body in the race and what affect it has on the total load and driving force.

You could hook up a fan that would blow air at approx. the speed of the car moving down the track and vary power as you would going into a corner and reapplying it. Sounds like a lot of work when about 5 laps on the track will tell you the same thing.

[Tropi]

A dynomometer certainly isn't the answer to everything!
But it is invaluable for assessing the basic characteristics of motors in isolation from all other effects. Eliminating as many variables as possible is always desirable in scientific decision making. Once you have your basic info, then you can methodically check combinations of factors.

In the end, of course you do have to mount the motor in a car and run it on the track. But prior use of a dynomometer can produce a lot of useful information very quickly. Particularly handy for quick comparisons of several motors without having to build them into cars (and take them out again afterwards). For instance, knowing that a motor is down 25% on power is likely to save the bother of ever mounting it in a car. Then you can work on the motor alone until it develops the characteristics you want. Or trash it, whatever!

Like any other measurement tool, you have to learn the significance of the information obtained in order to use it effectively.

It's just one of the tools available for turning a black art into a semblance of science. It ain't compulsory! :)

[anonymous]

Multiracer, if you race at the Mineral Ridge track,
ask Chris P. about his. Mike B.

[multiracer]

Great replies fella's.
Thank you