[a Bill]

What do you use for testing and checking motors? Obviously a visual inspection is important but what do you do to test for torque, rpm etc?

Currently I am just using my eyes and a DVOM. I also use spray cleaners for electronics and an ultrasonic cleaner for cleaning the things. For whatever reason, people keep asking about rpms and torque. I can't check them. I used to do comparative testing of motors by using the motor being tested to spin a heavier permanent magnet motor. The power leads from the heavier motor were hooked to the DVOM and the voltage made told me if the motor being tested was more powerful than whatever motor it was being compared to.

I noticed the 1/24th people use numerous hones and what look like dummy arms for checking and setting clearances on their motors. Is this something worth looking into? I want to make sure I'm not going too far afield and straying from what is important on these toy cars.

I stink at painting bodies and making them look realistic but I seem to do OK with the mechanicals so I tend to spend hours on an armature and maybe two seconds seeing if the body is still intact

 

[McLaren]

Damn straight! Mechanics over asthetics...

Anyway... I use my ears mainly to listen for higher pitch (more RPM) and rattling sounds (gonna blow up soon...). If I really need to know the RPM, I either use my friend's (250GTO's) Kelvin Light testing bench, a homemade Voltmeter bench (like the one you described) or a mini tacho which is meant for RC planes.

To use any of them, you either put the car (with the motor in) onto the bench and the wheels will turn a roller, or you have to place some reflective foil on the wheel, and RPM is measured by a light sensor.

The cheapest option is buying a mini tacho like mine from an RC model shop. Contact your local store for details...

Hope this helped.

Lotus

 

[Difflock]

I'm still at the stage where I chuck the car on the track and race

Actually I've taken to hooking up a 1.5 volt battery and leaving the motor for an hour or so to "run it in". If the car's slow then swap the motor

(bloody luddite I know!!)

Regarding the mini tacho using the foil on the wheel, won't you get varying rpm results depending upon the diameter of the wheel, unless you use the same wheel for comparisons? Taken to an extreme, a wheel twice the diameter would surely give an rpm result half that of the small wheel because the foil takes twice as long to come round.

Mark.

 

[cheater]

Mark wrote:

"Regarding the mini tacho using the foil on the wheel, won't you get varying rpm results depending upon the diameter of the wheel, unless you use the same wheel for comparisons? Taken to an extreme, a wheel twice the diameter would surely give an rpm result half that of the small wheel because the foil takes twice as long to come round."

Mark, this is simply wrong. RPM is not diameter dependent.

A point on the circumference of the larger wheel will move at a faster speed, if it is rotating at the same RPM as the smaller wheel.

If the reflective foil on the twice-diameter wheel "takes twice as long to come round," then that wheel is turning at half the RPM of the smaller one.

 

[ProfFate]

Hi

I am one of those 1/24 hardware guys with themagnethone and all. Yup it works.

The thing is, is it worth your time to spend several hours on a buck motor? There is so much slop in these things that working on them is almost self defeating. You CAN work with the FT motors in the SCX cars and all the tools work here.

Anyway, I havent found RPM too useful, or in fact any of the usual quoted specs. What I do is first throw the motor in a couple of standard test mules to see how they make power in a standard set up. Have a little dyno.

But ultimately, I put the car on the track and see what the clock says.

Fate

 

[Wankel Ickx]

I notice Fergy is lurking as I post....

Regarding SCX motors I now (thanks, Fergy!) take the brushes out of each new one I buy and wire the thing up to a meter to get a reading of... something.

The lower the reading of... thingies, the faster the motor goes.

I also occasionally tweak the springs to give more pressure on the brushes before I reassemble it all. I think the jury is still out for me on whether or not that does much but at least I can be sure I have the best motor in a car that I would like to be fast.

 

[Fergy]

Wankel!

Yes, arm resistance (ohms) will not always indicate a fast arm, but as you have found, it is often an indicator of potential.

One of the great things about those SCX motors is that you CAN play around with them a bit!

 

[Difflock]

QUOTE (cheater @ 21 Jun 2004, 16:32)Mark, this is simply wrong. RPM is not diameter dependent.

A point on the circumference of the larger wheel will move at a faster speed, if it is rotating at the same RPM as the smaller wheel.
D'OH!!

Where's the D'OH Icon when you need it

Mark.