Originally Posted by howardcano (Post 14259159)

I know of no flywheels that are both specifically made for our motors and affordable. For production, the cheapest solution that I can think of is to use a cast-iron V-pulley of an appropriate size (2.5" or so?). But it would have a little more surface area, and therefore drag, than necessary. If the losses are compensated for, that shouldn't be a big deal.

Originally Posted by pphaneuf (Post 14263213)

Do you know of some that, um, would be expensive?...
Someone with access to CNC equipment could get something quite nice... :)

Originally Posted by pphaneuf (Post 14263213)

About the weight of a flywheel being too much to mount directly to the motor without support, a greater diameter flywheel of the same mass would have a similar MOI as a heavier, smaller one, right? Mass near the centre doesn't help increase the MOI as much, so you could mill it out, to make it spoked (would need to balance it after, most likely!).

Originally Posted by howardcano (Post 14263722)

Yes, larger diameter does give more MOI for the same mass. But it also gives more leverage on the motor shaft for secondary imbalances, more aerodynamic drag, and reduces the maximum operating speed. Spokes may look nice, but for drag and structural integrity, I would prefer to stick with a solid disk.

Originally Posted by howardcano (Post 14263722)

Since I'm going to be using a gear drive, I can easily select the MOI that the motor "sees" by varying the ratio, which makes it easier to get good results with a large variation in flywheel sizes. That's important when being forced to use what's available, rather than what is optimum.

Originally Posted by pphaneuf (Post 14263852)

I'm now thinking it might not matter anyway, if we don't care about converting to real units? As in, if one setting goes from 5,000 to 5,075 RPM between two samples (at fixed time intervals), and another setting goes from 5,000 to 5,100 in the same interval, the second is better, and it doesn't matter if it could have gone to 5,150 without the gearing, right?

Originally Posted by pphaneuf (Post 14263852)

And it should be possible to compensate for the effects of gearing by looking at the deceleration curve when spinning down, right?

Originally Posted by howardcano (Post 14263719)

Several RCTech users are building, or have built, dynamometers ("dyno" for short), but there is no generic thread where we can all come together and share our experiences and show off our projects. So here it is!

Originally Posted by Mudcat981 (Post 14264241)

I would run it in free mode then flip the switches one at a time and apply the resistive load to see how the motor responded to loads from a start and from a running motor. Worked very well to determine RPM motors and torque motors.

Originally Posted by Mudcat981 (Post 14264241)

Plus it was great when you could change brushes, springs, timing, etc. Lot more tuning options than with today’s motors.

Thought of building one again, but with so limited tuning options, the G-Force motor analyzer reads timing and RPM plus amps, though does not check loads is sufficient for now.

Originally Posted by pphaneuf (Post 14264274)

The only thing with a slave motor and resistive load is that it can't go very low, and you have only very granular resistance, which will slow it down to a certain level (so you only get the torque at the RPM that it'll go down to).

Or does it?

Would a slave motor with a set resistance could be used in place of a flywheel to do a spin up, to get most of the torque curve? It wouldn't go all the way to zero (it'd stop short of the free running RPM), but would it generally work for the rest of the RPM range?

I'd be a bit worried that the torque reading wouldn't be linear through the RPM range, but if you optimize for each given RPM (use the timing that gives you the best torque at each RPM), it could make sense, right?



For blinky, there's not much to tune, but for boosted, there's a lot of information that you need to optimize the motor, and that's information a dyno can give you (more or less) easily. :)

The G-Force motor analyzer sounds good enough for blinky, IMHO. Getting the true timing measurement from each sensor is good for getting (more) consistent results from one motor to another, and the amp reading can let you see how much timing is too much. ;)

Originally Posted by Mudcat981 (Post 14264446)

It was only a $15 (poor man's) dyno :lol: It was a good indicator of motor performance (top RPM and AMP draw). :tire: To design what you are asking will cost $$$$$.

Originally Posted by Roelof (Post 14263953)

I do like the idea to measure data on the track:
http://www.rctech.net/forum/nitro-ro...mes-alive.html

It is possible to compare data to see if there are improvements.

Originally Posted by pphaneuf (Post 14264274)

Would a slave motor with a set resistance could be used in place of a flywheel to do a spin up, to get most of the torque curve? It wouldn't go all the way to zero (it'd stop short of the free running RPM), but would it generally work for the rest of the RPM range?

I'd be a bit worried that the torque reading wouldn't be linear through the RPM range, but if you optimize for each given RPM (use the timing that gives you the best torque at each RPM), it could make sense, right?

Originally Posted by pphaneuf (Post 14264480)

The RC Benchmark dyno that recently came out is just shy of US$450! It looks like the current version is aimed at other applications than RC cars (like quadcopters, robots, etc), but they seem interested in developing something that would be good for car racing... :)

Originally Posted by howardcano (Post 14264491)

It's not difficult nor terribly expensive to use an electronic current sink (controlled by a microprocessor, of course!) on the slave motor to vary the load on the motor under test. That's how the fancy dynos for brushed motors worked. But torque output needs to be measured with a separate sensor like a strain gauge to get good accuracy. Just measuring the current loading the slave motor isn't good enough.

The slave motor could simply replace the propeller as the load on the RCBenchmark dyno, since it already has a strain gauge to measure torque.

The flywheel dyno still gives more complete data in a shorter time, but if one needs to run a motor under a continuous load for an extended period of time (perhaps for stress testing), then the absorption dyno the proper device.

Originally Posted by Roelof (Post 14263953)

I do like the idea to measure data on the track:
http://www.rctech.net/forum/nitro-ro...mes-alive.html

It is possible to compare data to see if there are improvements.