Two Brushless motors on One ESC….YES!

[questtek]

It can be done and here are my video test results…http://www.youtube.com/watch?v=zeYAW...=youtube_gdata

There appears to be more and more multiple brushless set ups for FE boats recently. Twins are common but triples and even quad setups are being built and discussed on various OSE threads. Is it possible to run multiple brushless motors on ONE ESC in multiple motor set ups? I did some web research and the general opinion is that:
1. It probably will not work
2. If it does work it works only on small CD ROM-type motors
3. It will damage your motors and ESC’s
4. The back EMF will cause confusion to the motors that they will jitter
5. You will have a very difficult time trying to start BOTH motors together
6. Etc, etc

Here are some of the links I used in my web research…………

RC groups thread……..

http://www.rcuniverse.com/forum/m_4877831/tm.htm

WattFlyer thread…………….

http://www.wattflyer.com/forums/showthread.php?t=9264

Hobby King Forum discussion…………
http://www.hobbyking.com/hobbyking/f....asp?TID=14234

So, being curious and thinking about a real exotic multiple brushless motor build, I decided to run some actual tests with moderate size brushless inrunners and outrunners. I went all the way up to two Leopard 4074’s running on one SeaKing 180 ESC as shown on the video

http://www.youtube.com/watch?v=zeYAWqt2rIE&feature=youtube_gdata

NOTE: I am not recommending or endorsing the use of a single ESC for multiple motors I just wanted to point out that my experiments proved it was not only possible but actually worked quite well. Naturally in such a configuration the ESC must be matched to the COMBINED AMP DRAW of both brushless motors. Now it’s time for some actual load tests and more experiments!

[BakedMopar]

Im in on this one.

[ManuelW]

Hello,

first I have to say thanks for testing it and nice that it "seems" to work. In the German Forums this topic was discussed either.
Especially in some of the last threads some Pro's discussed it and they came to a conclusion.

As known the Brushless Motors we use are sensorless, the ESC's reads out the position of the rotor with Back-EMF. They didn't test it but assumed as your test showed, that it can work with 2 unloaded motors. Then the controller has no problem to get both motors to the right rpm. It will probably also work when both motors have nearly the same load, eg in planes. Because when the prop size is the same, the load as well as the rpm should be the same.

The big "but" is, the different loads the bigger the problems. This means in tests with planes the controllers as well as the engines worked but got very hot due to inefficiency. And all the experts did have the same opinion that in a boat it won't work. Worst case: Twin engine boat, one prop gets out of the water and runs completely free, the other one has full load.

But I like your test and it really surprised me how nice it seems to work without load. Next test would be, wether it works when you simulate different loads.

Best regards,
Manuel

[questtek]

Hello,

first I have to say thanks for testing it and nice that it "seems" to work. In the German Forums this topic was discussed either.
Especially in some of the last threads some Pro's discussed it and they came to a conclusion.

As known the Brushless Motors we use are sensorless, the ESC's reads out the position of the rotor with Back-EMF. They didn't test it but assumed as your test showed, that it can work with 2 unloaded motors. Then the controller has no problem to get both motors to the right rpm. It will probably also work when both motors have nearly the same load, eg in planes. Because when the prop size is the same, the load as well as the rpm should be the same.

The big "but" is, the different loads the bigger the problems. This means in tests with planes the controllers as well as the engines worked but got very hot due to inefficiency. And all the experts did have the same opinion that in a boat it won't work. Worst case: Twin engine boat, one prop gets out of the water and runs completely free, the other one has full load.

But I like your test and it really surprised me how nice it seems to work without load. Next test would be, wether it works when you simulate different loads.

Best regards,
Manuel

Good feedback and now that I have the actual test set up I can even do load testing. I just tried to run a 540 XL and an outrunner on one SeaKing 180 ESC. They started OK but due to the radical KV differenct, 2084 vs about 1200 kv, there was a lot of jittering and sputtering starting about half throttle no-loat.

Based on this simple test I am pretty sure the motors should be of the same type, size and KV for it to run properly. However, it's the actual load tests that should provide the most interesting results.

It goes without saying I plan to run the same type, kv motors with identical props on my first loat testing. I already have a Mean Machine set up with Dual 4074 Leopards. I am pretty sure a single 180 Seaking will NOT support both motors at max draw, however 1/2 to 3/4 throttle should tell me quite a bit. Unfortunately we have heavy rain here in SO Ca till Friday so it will be a few days for the lake testing

[questtek]

With the heavy rain curtailing actual lake load runs, I resurected an old test tank I built up for a previous thread I posted on ESC cooling. I used this test tank to evaluate different ESC cooling methods on the bench while tied into an Eagle Tree system linked to my laptop.

From the pictures you can see I have already mounted two 540 XL motors and a 180 Seaking ESC with my "Y' connectors to the motors. I still need to drill the top and align the dual shafts. The large props I use will provide the load for the motors. It should be interesting....

[keithbradley]

Im always interested in people testing things for themselves. Hats off sir.
I would error on the side of less load...if you have small identical props to test adn lower kv motors, it would make sense to start with that. Motors can still pull a ton of current at light throttle if the load is high enough.

[questtek]

Im always interested in people testing things for themselves. Hats off sir.
I would error on the side of less load...if you have small identical props to test adn lower kv motors, it would make sense to start with that. Motors can still pull a ton of current at light throttle if the load is high enough.

Good suggestion but I will have an Eagle Tree hooked up to my laptop and the ESC/Motors system. I will keep the amps on the "reasonable" side. Not too worried about blowing up the 540 XL's ...I just do not want to trask two brand new Leopards! Should be intresting and have great application.....IF it works!

[jimbo--jones]

Thats brilliant!
I got one question. Where did you get the Y bullet connectors from?

I never understood why you cant run 2 motors on one esc. I figured if both motors are the exact same ( resistances) it will work.

[keithbradley]

Good suggestion but I will have an Eagle Tree hooked up to my laptop and the ESC/Motors system. I will keep the amps on the "reasonable" side. Not too worried about blowing up the 540 XL's ...I just do not want to trask two brand new Leopards! Should be intresting and have great application.....IF it works!

Are you going to do a control run of these motors? It would be usefull to run them alone at the same throttle amount and monitor temp rise relative to time when compared to running them in pairs. I wouldnt be the slightest surprised if there were some timing issues that caused higher temps when running 2 motors, but you dont know until you try.

[photohoward1]

Put a load on one Motor and not the other. Bet it fries something. What happens when one motor outside in a turn is spinning free and the inside motor bights the water?

Timing will be all off for the controller.

HT

[GeoVW72]

I have also put some thought into this concept, definitely curious to see where it goes

[questtek]

Thats brilliant!
I got one question. Where did you get the Y bullet connectors from?

I never understood why you cant run 2 motors on one esc. I figured if both motors are the exact same ( resistances) it will work.

Just made the "Y" connector. If this works I will make a 3-motor connector.

Agree with you...both motors probably have to be the same. The big question is what happens when one of the two motors becomes "unloaded"? Only more testing will tell......

[questtek]

Put a load on one Motor and not the other. Bet it fries something. What happens when one motor outside in a turn is spinning free and the inside motor bights the water?

Timing will be all off for the controller.

HT

Good point and easy to test. I will give it a try.

[graill]

Heh, This simply cant end well......

[questtek]

Heh, This simply cant end well......

But at least you will learn why it can't be done..........

An interesting point was brought up when one motor is no load and the other under load. So, I did a test with the two 540 XL motors. I left one free running at no load and put a very heavy load on the other, almost stall, and they recovered just fine. No jerking or shuttering. I repeated this several times but it was always the same. It appeared the RPM slowed down a bit on the unloaded motor but without a tachometer or Eagle Tree on it I would not know just how much. Testing your concern gave me a bit of renewed confidence.