Why no dyno for brushless?

[scoob]

Why can't brushless motors be run on a dyno. I assume they can't because I've never heard mention of it.

[tcolesen]

Good question. Maybe it's because they would overload the dyno ;). I don't think it would be proper to use a dyno, since a BL motor's highest efficiency can be rather high (60amps or greater!), and the motor would need quite a load to pull that many amps. The motor's torque output is a function of amps, so as the amps go up, torque does also. It's just that a BL motor will operate on such a wide range that a dyno graph would be pointless (IMO), even if multiple graphs were used to display results at different amperages.

[Rtsbasic]

But a varying load dyno could be useful for comparing to other brushless motors?

[glassdoctor]

Of course a dyno could be used for BL. A motor is a motor and the dyno doesn't care.

The reason we don't see it I think is just becasue the guys who are into brushless are not typical "factory racer" types and don't have a dyno laying around to play with.

In full scale cars, the same dyno is used for gas vs. diesel... carbureted vs. supercharged... etc. right?

It would be very cool to see a full list of dyno tests on various bl motors. There are endless possibilities of what could be tested, like even the difference between controllers using the same motor.

Anyone have access to a dyno? :)

[scoob]

Of course a dyno could be used for BL. A motor is a motor and the dyno doesn't care.

The reason we don't see it I think is just becasue the guys who are into brushless are not typical "factory racer" types and don't have a dyno laying around to play with.

In full scale cars, the same dyno is used for gas vs. diesel... carbureted vs. supercharged... etc. right?

It would be very cool to see a full list of dyno tests on various bl motors. There are endless possibilities of what could be tested, like even the difference between controllers using the same motor.

Anyone have access to a dyno? :)

I agree, I think it would be nice to see some numbers.

I see your point about everyone using brushless not being factory racers but you'd think someone with a dyno would have run some to see how they compare to thier current brushed setups if it were possible. :confused:

I also know that most people use dynos to tune thier brushed motors and you don't really tune a brushless, at least not conventionally, so maybe that's it?

If you could hook up to one of the brushed dynos, we'd finally know how the 6 cell motors compare. Everyone seems to have a different opinion how a motor( like the Novaks for instance) compare to brushed( what turn).

[SpEEdyBL]

You don't need a dyno for brushless since there are less variables. As long as you know voltage of the battery, the voltage drop of the battery as a function of amps, the resistance of the motor and the motor's no-load current, you can find the max efficiency and power out put. You can use graphing calculator to see the graph. Power output = volts x amps - motor resistance x amps^2 - no-load current x volts. Funny thing, I found this equation when trying to find equation for power output with kt, kv and resistance and it simplified out to that. Btw, efficiency = Power output/(volts x amps). rpm drop per amp is kv x motor risistance.

One last thing. Does anyone know what the voltage drop of a battery is as a function of battery resistance?

[kufman]

Here are the results of my very basic dyno that I made using a two motor gear drive, a brushless slave motor and some resistors. I powered it with a 5V supply for all of the motors. In the future I will add a current meter to it. Right now I just have three load levels. The first one is just the resistance of spinning a basic 4200 with no load on its terminals. #2 and #3 have resistaers on the wires of the basic 4200. The horizontal axis is the 3 load levels and the vertical is RPM as measured with an oscilloscope.

One last thing. Does anyone know what the voltage drop of a battery is as a function of battery resistance?

V = I*R Your voltage drop should be the current times the resistance. This is purely due to the "equivalent" resistance of the cells and doesn't take into account any effects of chemistry of the battery.

[glassdoctor]

Interesting...

You can see that the stock motors have more rpm than the 19T in the first run, but drop off under more load and both 19T pull ahead.

What do you est. the current loads are in #2 and 3?

[kufman]

with my one stock motor, "new monst" the current load at #1 was 9.6A, #2 was 17.3 amps and at #3 it was 22.3A. That one I took to work and used a current clamp on.

[BobNovak]

Here are the results of my very basic dyno that I made using a two motor gear drive, a brushless slave motor and some resistors. I powered it with a 5V supply for all of the motors. In the future I will add a current meter to it. Right now I just have three load levels. The first one is just the resistance of spinning a basic 4200 with no load on its terminals. #2 and #3 have resistaers on the wires of the basic 4200. The horizontal axis is the 3 load levels and the vertical is RPM as measured with an oscilloscope.



V = I*R Your voltage drop should be the current times the resistance. This is purely due to the "equivalent" resistance of the cells and doesn't take into account any effects of chemistry of the battery.
Nice litle project that you have there. We at Novak built a very basic dyno when we first started designing the Super Sport System and still use it today to compare our brushless motors with brushed motors or other brushless motors. It basically is a flywheel dyno that measures the rpm and current from a standing start ( zero RPM) to full speed and will run a standard brushed motor thru a brushed speed control or a brushless motor thru a brushless speed control. The one problem that we have with it is when we try to dyno a sensorless brushless system. On startup all the sensorless brushless systems that we have tested will make the flyweel oscillate back and forth and will never get started. You have to manually spin the flywheel by hand to get it started. This is the main reason we decided that sensorless was not the way to go for cars. The heavier the load the worse the problem. By the way on your dyno it looks like the Super Sport had the highest power output. Am I reading this right?
Bob Novak

[tcolesen]

The one problem that we have with it is when we try to dyno a sensorless brushless system. On startup all the sensorless brushless systems that we have tested will make the flyweel oscillate back and forth and will never get started. You have to manually spin the flywheel by hand to get it started. This is the main reason we decided that sensorless was not the way to go for cars. The heavier the load the worse the problem. By the way on your dyno it looks like the Super Sport had the highest power output. Am I reading this right?
Bob Novak

Bob, have you tried any newer controllers? Ones like the Mtroniks and MGM have almost zero cogging on startup, but of course the actual amount will depend on gearing and motor choice. Newer sensorless controllers are getting so smooth that I may never go sensored like I though I would at some point (just because I was having problems with oversees service, but Mtroniks seems good).

[Rtsbasic]

Personally, I've recieved much better quality of service from Mtroniks than Novak (in the UK), but thats a whole different subject. I do like being only a phone call away from speaking with someone who actually cares about their customers.

I would love to see a dyno graph of various Feigao motors sometime, but don't have the facilities to do it. With newer controllers I don't think there would be as much of a problem starting, this is one thing recent controllers seem to have been getting pretty right.

[SpEEdyBL]

Nice litle project that you have there. We at Novak built a very basic dyno when we first started designing the Super Sport System and still use it today to compare our brushless motors with brushed motors or other brushless motors. It basically is a flywheel dyno that measures the rpm and current from a standing start ( zero RPM) to full speed and will run a standard brushed motor thru a brushed speed control or a brushless motor thru a brushless speed control. The one problem that we have with it is when we try to dyno a sensorless brushless system. On startup all the sensorless brushless systems that we have tested will make the flyweel oscillate back and forth and will never get started. You have to manually spin the flywheel by hand to get it started. This is the main reason we decided that sensorless was not the way to go for cars. The heavier the load the worse the problem. By the way on your dyno it looks like the Super Sport had the highest power output. Am I reading this right?
Bob Novak

Why aren't there any power/kv ratings for the velociti motors? What are they?

[kufman]

By the way on your dyno it looks like the Super Sport had the highest power output. Am I reading this right?

Yup, the SS had the highest output of the motors tested. If I nailed the throttle on the lowest load, I tripped off my supply. I need to get a better 5V supply to test higher performance motors. It is only a 23A supply and that isn't much current when you are testing 50% efficient brushed motors. I could always take it to work where we have power supplies of just about every power level imaginable.

sensorless motors do have trouble spinning a flywheel, but they have gotten better is the last couple years. My Hacker Sport had trouble starting a motor with an airplane propeller on it! My U-force on the other hand, has no trouble and works well in pan cars.

[GordonFreeman]

Bob, hmm..I wanted to build a small inertial dyno (flywheel) for testing. I thought you would want a mass that would simulate real life motor acceleration. What was/is the aproximate size/weight of the flywheel? Any gearing?

Getting sick of using propellers and it's too hard to get accurate efficency numbers, I think.

[kufman]

Here is a newer dyno sheet using a couple of battery packs in parallel and a new slave motor. "Kisby" is a stock motor that is in the last sheet as well.

[Key]

Newer sensorless controllers are getting so smooth that I may never go sensored like I though I would at some point (just because I was having problems with oversees service, but Mtroniks seems good).

I agree with you on this point and would personally not go the sensored route due to their present limitations.

My U-Force75 esc are steps ahead of sensored units in terms of high amp, high quality, low speed smoothness, Lipo friendly, motor options, pc compatibility and the list goes on...

-Key

[Key]

Interesting numbers but not surprised.

The Pletty maintains it's efficiency over a wider range which is why they make excellent car motors.

[kufman]

The motor that really holds it's rpm is the lehner 4200. If I had another load level, the 4200 and shadow would probably be equal. this is probably due to battery limitations, but that is true to real life. You are not going to be running 4 packs in parallel when you use it in a car. I noticed that both lehners and plettenbergs graphs show constant voltage comming in. They must have used a fairly well regulated power supply to do the tests.

[Craps]

My team has 6 Plettenberg Extreme and like all motors, everyone is a little different with power or throttle curve. It is small differences and would like to find away to scientifically measure those differences with a computer dyno?

I would also like to measure the Schulze U-Force 75 ESCs against each other too because I suspect the ESC maybe different too instead of the motor in every case?

With the West Mountain battery analyser, I can check my batteries performance wise and can report all 6 TP8000-2S4Ps I just got in are all equal to each other. The 1 thing about Thunder Power li-pos, they are created equal, but there is difference in chargers. I have 3 Astro Flight 109s and 1 Duratrax Ice and all of them in a small way peak the battery at different voltages. None of them compared to a digital voltmeter peak it exactly to the 8.4 volts the charger reads out!

[tcolesen]

I have 3 Astro Flight 109s and 1 Duratrax Ice and all of them in a small way peak the battery at different voltages. None of them compared to a digital voltmeter peak it exactly to the 8.4 volts the charger reads out!

That's because the AF 109 isn't a CC/CV charger, but the ICE is.

[Craps]

I use the AF 109 for my li-pos because the ICE is way to slow! I use the ICE to charge my TX batteries!

[SpEEdyBL]

8 amps too slow? I thought the 109 does only 7.5 amps max.

[BobNovak]

Bob, hmm..I wanted to build a small inertial dyno (flywheel) for testing. I thought you would want a mass that would simulate real life motor acceleration. What was/is the aproximate size/weight of the flywheel? Any gearing?

Getting sick of using propellers and it's too hard to get accurate efficency numbers, I think.
Dear Gordon,
Sorry for the late reply but I have been out of town to the Novak Touring car Championships in Milwaukee. If any body is interested in the results they are posted on our website @ www.Teamnovak.com. Anyway the flywheel is 745 gms (26.28 oz) with a diameter of 2.725 in. The problem you will have is that you need a power supply that will put out at least 150 amps. Ours is adjustable from 0 to 350 amps. We do not use any gearing and with some of our real low turn brushless motors the rpm realy gets scarry fast. Here are some typical numbers from a Velocity 5.5 turn Brushless motor. At 0.1 sec RPM=3757, I=126.7amps, at 0.2sec RPM=7763, I=120.97amps, at 0.3sec RPM=11329, I=113.57amps and max RPM=33127 at I=12.7 amps. Voltage input is 5 volts. This gives a Kv=6625.4 at 12.7 amp load. This Kv is realy the Kv of the system as there is voltage drops in the power wires and speed controll, but they are small. Hope this helps.
Bob Novak

[OptimaMan]

hey, this is awesome... I had the GTB 5.5 Kv to be approx 6500 based on my eagletree tests under 30 amp draws and about 6200 around 50 amp draws. Looks like our info is pretty close there.

[kufman]

Anyway the flywheel is 745 gms (26.28 oz) with a diameter of 2.725 in. The problem you will have is that you need a power supply that will put out at least 150 amps. Ours is adjustable from 0 to 350 amps.

Is this really a good test? Batteries are not going to hold up their voltage at 100A so how useful is the data generated by using a constant voltage source going to be? I see the fantom dyno have the same problem for brushed motors since you can basically use a car battery for that dyno. The voltage in the batteries alone (for 17m-ohm battery pack) would be 1.7 volts at 100 amps.

So here in my question, is a motor that is optimized on a infinite current source, optimized for running on a battery pack?

[OptimaMan]

Even though testing with an unlimited power might not be absolutely ideal, it will give us a way to compare motors. In addition, a 6 cell pack at 100 amps still will maintain voltage over 6.0 volts