So how do you measure torque?

[Talico]

There is a lot of talk on here about torque, but I dont see anyone explaining how to measure it, even just comparitevely. Anyone built a De Prony brake to measure torque? Or when you talk of torque do you just mean it as a function of power at rpm?

[Charlie-III]

Most are using a calculation. There are some dyno's that "measure" torque with a small flywheel or magnetic field, but my understanding is that it tends to be inconsistent.

[OfnaJoe]

I use my Phanton dyno for my RC stuff. And for my 1:1 'Stang I see how far the front wheels come off the ground and the tree.

[Talico]

Wow! That Phanton is seriously expensive, especially from this side of the world(South Africa). I once build a kind of a "dyno" for my slot cars when the kids argued about losing because they got the slow car. That was just the wheels rotating a mass and I measured the voltage generated by this, so just rpm under load. That seemed to work fine for comparison purposes of power but I don't think it will indicate amount of torque.

[EddieO]

A dyno is main the way its measured....

A Turbodyno actually has a Torque Sensor to measure the torque. As the motor runs in the dyno it will cause strain against the carriage that holds it, which is connected to a torque sensor. The main problem with the Turbodyno torque sensor is it only measures to 16 oz of torque, which most crawler motors have no problem exceeding.

The fantom or the robitronic are flywheel dynos, both of which simply use a flywheel attached to the motor to measure certain characteristics. There is no torque sensor though, so both machines use formulas based on acceleration, amp draw, and rpm to calculate the torque and overall power of the motor.

There are other dynos out there, but they are not used much.....these were the main 3 by far.

Later EddieO

[OfnaJoe]

I had a Turbodyno and didn't like it, kept getting different reading on the same motor from back to back pulls. I guess it was all from how the motor torqued in the holder.

[EddieO]

Thats the main gripe with the Turbodyno, its unlike a flywheel, you have issues with consistency. This is caused by the slave motor needing to be rebuilt. If you have inconsistent readings from a motor from pull to pull, the slave motor needs to be rebuilt. This clears up the problem 99% of the time.

When it was all said and done, the Turbodyno was used by Jim Dieter, Mike Reedy and Oscar Jansen, among others in racing. Those 3 were considered the best motor tuners in the world, and of all time.....

Later EddieO

[Charlie-III]

A few things to keep in mind about ANY dyno (RC and 1:1).

1-They can be good for checking changes on a motor or vehicle.
2-They suck when comparing values from one dyno to another (even if they're the same brand/model dyno)
3-Electric motors accelerate VERY fast, thus the time span to do measurements is very short. Any tiny error/inconsistency creates large errors in torque values.

This is not even getting into differences in set-up/calibration of a dyno, wear, variances in input power (RC dynos).

I use a simple load based "dyno". I use it for before/after testing. I have no good way to compare my numbers to anyone else, but don't really care.
If I plot out graphs, I can get an idea of my motors compared (sorta) to other peoples motors. Just looking at the basic shape of the graph.

In the Subaru world, there were dyno brands that would give "Great numbers" and others that were "Heart-Breakers". A car dynoed on a heart-breaker could out run a car with great numbers in the 1/4 mile.
The stopwatch won't lie.

[Talico]

Hey Charlie can you explain more about your load based dyno? Sounds like something I might be able to build.

[Charlie-III]

Originally Posted by Talico

Hey Charlie can you explain more about your load based dyno? Sounds like something I might be able to build.

I have:
Large power supply (so input power won't change)
Series of resistors (so I can vary load using toggle switches)
Slave motor
Light type tach (to measure RPM at each load)

It was built off of plans from an RC magazine in the mid 80's. Basic but useful for me.
I don't have plans anymore but could likely draw up some basics. There is also some building to mount the slave motor, case, etc.

You can find used dyno's on the Internet.

[OfnaJoe]

Yup, I only really used mine to find my best motors, and see what different spring combos would do and different cuts on brushes. Even got a Gause meter to chech the cans. Was "Real" heavy into 1/10 oval

[Talico]

So you would be looking for highest rpm at the same voltage?

[Charlie-III]

Originally Posted by Talico

So you would be looking for highest rpm at the same voltage?

Depends on the track/use.

Oval we went for speed (high RPM for a given voltage)
Road course we went for torque (high RPM for a given load)

Different compound brushes and spring tensions were 2 easy changes for these values.
A hard brush/light spring combo could help top end as an example.

There were also little differences between motors (we used a lot of "epoxy sealed" 27T track motors) that made some better for oval while others were better for road course. Since they were sealed, it was harder to make major changes to the motor internals.
We used to buy as few motors and dyno them as a baseline. Then sort them into oval or RC and go from there.
As they became tired, we would use them for practice motors and save our good motors for races.

I used to keep one "gold standard" motor to test the dyno itself, it was NEVER raced. When the slave motor needed a service, I could see the numbers drop off in the "gold standard". This way, all my numbers remained relatively constant for that specific dyno.

Hope this all makes sense.

[JohnRobHolmes]

A prony brake dyno could give you pretty good numbers. You could build your dyno stand with the test motor mount pressing on a simple scale for torque measurement. With a tach, voltmeter, and ampmeter you have the full gamut of readings needed for a dyno. Measure amperage on the test motor, measure voltage as close to the test motor as possible, and use the prony brake to get the exact amp readings you need. While you will smoke most motors trying to dial in the prony brake for higher amperage (takes too much time), you can get four to five good readings and draw out the rest of the motor curve in excel.