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=zeYAW...=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.

[LiPo Power]

This is very cool...
Cant wait to see your resoults with no load on first and load on second motor.....

[questtek]

This is very cool...
Cant wait to see your resoults with no load on first and load on second motor.....

Here are the test results with the first 540 XL under NO LOAD and the second 540 XL loaded by using a prop turning in a water filled test tank. The picture shows the test set up.

Here is the video of the tests and you can see it appears in this particulat test set up that it appears to work quite well.
http://www.youtube.com/watch?v=NFrC6...=youtube_gdata

[Jesse J]

Very interested in this... I have a quad motor project stewing on the back burner, would be great to only have to use 2 ESCs - doubt I could get all four through one ESC...... who knows?

[sundog]

Try loading the unloaded motor (pinch the shaft?) while performing the same test. Will the submerged prop motor respond by slowing down to match the problem (pinched) motor? This is way cool......& much cheaper than frying my own. Keep up the good work!

[questtek]

Very interested in this... I have a quad motor project stewing on the back burner, would be great to only have to use 2 ESCs - doubt I could get all four through one ESC...... who knows?

Exactly the point I was considering........... My test plan is as follows so stay tuned today:

1. Continue tests with 540 XL' on on Seaking 180 with Eagle Tree set-up. Some say the motors will stall if you accelerate fast. Some say the amp draw will be way too high, etc. Myth busters here I come....................

2. Try the same set up but the two new Leopard motors 4074 at 2200KV each. Again, using the Eagle Tree, look at what happens as the loads become more and more mismatched, etc.

3. Build up jumpers to do 3 and 4 motor testing. Fortunately I have 4 new matched Leopard 4074 motors an this will be my focus on testing. I do not have a third 540 XL or I wouild start with this on the three motor set-up. (I do have 4 of the match brusless motors so that might be my quad possibility.

Again, I a looking at s very specific motor/ESC combination. I cannot imply this will work on All brushless motors and All esc's. I am doing these tests to see if the old beliefs that" it cannot be done" is really a valid statement and at this point am only interested in a combination of motors and esc's that I will be using on future projects.

THE BIG CONSIDERATION IS THAT THE TOTAL AMP DRAW OF THE MOTORS WILL NOT EXCEED THAT OF THE ESC'S RATED CAPACITY. This concerns me with the Leopards because I can pull 140 amps with the Leopard in my Insane Hydro with the Seaking 180. Two motors pulling 240 aps out of a single Seaking 180, well, priceless.............................all the way to the trash bin.

[questtek]

Just found a post of a different site by Bernie Wolford of Castle Creations. His recommendations are in line with my test results so far.............

His previous comments on running two motors on one ESC..................
1. Two motors can run on a single controller -- but:

a. They must be very closely matched -- within 1% or so on Kv 1. If they are not perfectly matched, timing from the controller is AVERAGED between the difference on the two motors (this happens because the back-EMF voltages average when the wires are paralleled on the motors.) 2. This will cause higher surge currents to the motors-- and will tend to increase the temperature of the controller and motors.

b. They will not always start correctly (I have never had this problem but I only started the motor combinations about 20 or 30 times without a single non-start)
1. If they don't start correctly (for example, one motor starts, and the other does not) the controller can be damaged.

2. So, if two motors are run, they must be started on the ground, and there should be no attempts at restart in the air -- AND if one motor fails to start, the power should be shut down immediately.

So, my personal recommendations are that:

1. We recommend using two controllers to run two motors.
2. If the user runs two motors on a single controller, the controller should be derated by 30% (for example, a 45 amp controller should be used in an installation which draws no more than 31 amps on both motorscombined.) (This is really interesting to me and indicates that the Seaking 180 would be derated to a 126 AMP ESC and I can live with that. I just assumed it would be derated by 50% to a 90 amp ESC so this is actually good news)
3. If two motors are run on a single controller, the motors must be the same type and wind, and must be well matched.
4. The motors should be started on the ground, and not restarted in the air.
5.High inertia loads (for example, large props on very small motors through gearboxes) shouldn't be attempted in a dual motor installation.

[Steven Vaccaro]

This is very interesting and I commend your testing and posting of results. My issue is this, there are enough problems with esc's going south with just one motor connected to it and run within the esc's known parameters. Why chance problems when running 2 motor on one esc?

[questtek]

This is very interesting and I commend your testing and posting of results. My issue is this, there are enough problems with esc's going south with just one motor connected to it and run within the esc's known parameters. Why chance problems when running 2 motor on one esc?

All good points, Steve. I have found the SeaKing 180 and Leopard 4074 motor combo a bullet-proof system and I want to push it to the next level for several special projects.

The pictures show just one of them, a prototype of a Military, Hands-Free, Diver Propulsion System. Size is critical. If properly done, the RPM thus power and torque of the motors is perfectly matched.

Also just thought the FE community might be interested in the successes as well as failures of my testing in this area.

[questtek]

This should cause a bit of controversy....................

I am using a new unit of measure in my analysis that I do not think has been used before. The unit is RPM/watt. To determine this I have an Eagle Tree system on my test rig meauring watts, amps, RPM and temps. I will not bore anyone with the details just the punchline:

This is for BOTH motors unloaded condition:
1 motor 1 esc the result is 292.17 RPM/watt
2 motors 1 esc the result is 343.6 RPM/watt

The 2 motor set up takes into account that you are spinning two unloaded motors each at 11,300 RPM consuming 65.17 watts. In the single motor, single ESC set up you are turning a single unloaded motor 12,350 RPM and consuming 42.27 watts.

Now I really have to think about what this means.....................

[Flying Scotsman]

Very interesting thread, BUT real world conditions on an FE boat would be interesting, not a lab experiment, but I also commend you for trying it out.

Douggie

[blackcat26]

I think your testing is great but is it still not cheaper to run two esc's than one big one? The price gets crazy the bigger you go which has never made since to me. You can't tell me it cost the manufacturer double to produce a 240a versus a 120a........

[questtek]

Very interesting thread, BUT real world conditions on an FE boat would be interesting, not a lab experiment, but I also commend you for trying it out.

Douggie

Agreed,BUT, starting in the lab has already disproved many theories. It also alows me to closely measure what is happening. Too often when running a boat we "Think" it looks a little better bur just how much, Well????

The absolute most important reason is RAIN. It is, has been and will continue to pour down rain here in So Ca. These are some of the worst rainstorms I have ever seen. Winds are so high it blew my 16 foot electric boat away from the dock. Fireside testing with a gin and tonic...........that's for me in this weather!

[questtek]

I think your testing is great but is it still not cheaper to run two esc's than one big one? The price gets crazy the bigger you go which has never made since to me. You can't tell me it cost the manufacturer double to produce a 240a versus a 120a........

Is it? I buy the Seaking 180's for about $80 each. From Hobby King you can buy the 200 amp HiModel or Suppos for less than $50 and DIY water cooling. Another thing is that in some of my projects this concept 1 ESC, multiple Matched brushless motors may have some real advantages, cost issues aside. What about running a quad system with 4 of the Turnigy outrunners at 400 watts each on a single $50 to $80 Esc? May be a terrible idea, but it sounds at least interesting to me.

I generally try to avoid the conventional and experiment with different concepts since much of it has application to other marine products. Multiple brushless motor control, with matched motors, is right now a potentially interesting concept to me. I am still trying to think about what RPM per watt really means when we evaluate this type of system. Ideas?

I have attached pics of a QUAD controll jumper set I just made. I have 4 matched outrunners I would like to try them on. Using these jumpers I can run `1,2,3 or even 4 matched motors from a single ECS................or blow up that number also!

[Flying Scotsman]

Agreed,BUT, starting in the lab has already disproved many theories. It also alows me to closely measure what is happening. Too often when running a boat we "Think" it looks a little better bur just how much, Well????

The absolute most important reason is RAIN. It is, has been and will continue to pour down rain here in So Ca. These are some of the worst rainstorms I have ever seen. Winds are so high it blew my 16 foot electric boat away from the dock. Fireside testing with a gin and tonic...........that's for me in this weather!

A Scotch whisky might be better and I have been following the mad weather in Europe and the rest of world this month and yes your point of in the lab is observed.

Douggie

[questtek]

A Scotch whisky might be better and I have been following the mad weather in Europe and the rest of world this month and yes your point of in the lab is observed.

Douggie

Sure wish you were here to help me.............along with your Scotch! A fine malt I am sure.