Two Brushless motors on One ESC….YES!

**domwilson** · 12-22-2010, 10:52 AM

I'll be the first to admit that I was wrong about this. I guess you learn something new every day.

**sailr** · 12-22-2010, 11:08 AM

Your test tank video is great! You were saying 4C battery? I think you meant 4S? Also you were saying 1300 rpm when it looked like the eagle tree was saying 13000?

**questtek** · 12-22-2010, 01:37 PM

Originally posted by sailr

Your test tank video is great! You were saying 4C battery? I think you meant 4S? Also you were saying 1300 rpm when it looked like the eagle tree was saying 13000?

YOU ARE SO RIGHT, Sorry. I have a rough time patting my head and rubbing my stomach at the same time. I hold the camera, narrate the video and try to control the experiment, (while my wife is probably yelling at me in the background), so I get a bit confused at times................and glad you spotted it. You can be my video "proofreader".

**questtek** · 12-22-2010, 01:46 PM

Originally posted by domwilson

I'll be the first to admit that I was wrong about this. I guess you learn something new every day.

There is nothing to be wrong about...............this is all just tesing and seeing what does and does not work. I certainly was wrong in my assumption that possibly a single 200 AMP esc could run four $13 high KV Turnigy outrunners. Turns out it one ESC works fine (backed on my limited experiments), for higher, better quality outrunners. It DOES NOT work with a 4400kv $13 Turnigy H2223motor. I believe one reason that a 1% KV mismatch in a higher quality, low, 1200 KV motor is only 12 rpm and the ESC appears able to compensate for this small mismatch. For the higher, cheaper KV moters where the mismatch can be 3 or 4% this means you may have an rpm differnece of about 160 RPM between the motor and the ESC goes crazy. So, a quad brushless FE setup for under $100 does NOT really appear viable at this time.

I am going to continue on these experiments to see what else I do not know!

**LuckyDuc** · 12-22-2010, 02:08 PM

I have run 2 motors on one ESC in a EDF jet. It worked OK. The only time I noticed a problem was when I shut down power in flight and tried to floor it again. One motor started and the other didn't. It caused a flat spin. Pretty cool though. If this is for a scale boat project with low rpms and load, it should work fine.

Here is a video of the above mentioned plane before it met it's demise due to a wing bolt failure. If you watch you can see that the motors are not perfectly sync'd (This is most noticeable at 1:18) Pretty good crash at the end too.

**questtek** · 12-22-2010, 03:55 PM

The previous post inspired me so ...............

I did some additional testing with two of the $13 Hobby King Turnigy H2223 Outrunners on one ESC. It did not appear to work last night HOWEVER I discovered this morning that the motors were hooked up opposite. One in FWD, the other in reverse! I corrected the miswiring, making them both in the same conventional rotation and they did indeed work together.............even these cheap outrunners.

I purchased some 7 x 5 props but was told this is way too much for this engine so I then purchased two 6 x 4E's at the local Hobby store and attached them to the outrunners. The test set up in in the pics.

The motors are mounted to a digital bathroom scale. (I add 15 lbs of lead to the scale then unload it with the motors)

I am worried about the props shattering or flying off since the motors have a 4400 KV and I want to run them on 2-3 S. The heavy wire mesh basket from IKEA provides a good safety factor for this.

It was indicated to me that the motors would have excessively high amps pushing these props (they are rated at 600 Watts) so I wanted to try it. Here are the results with the 6 x 4E prop

1 brushless H2223 outrunner and one ESC
RPM AMPS Watts
20K 2.64 32.7
25K 3.65 45.1
30K 5.22 64.2
35K 7.55 92.3
40K 9.75 118.5

Several important points now:
1. All readings via Eagle Tree V3 data logger
2. Tests on the other outrunner were identical
3. the total mAhr consumed for this test was about 225 mAhr out of a 5,000 mAhr LiPo pac.
4. I assumed this is a two pole motor for the Eagle Tree brushless RPM sensor
5 I did not measure loads from the scale since these are just initial tests

Now with the two Turnigy brushless outrunners both with identical 6x4E props on ONE ESC:

RPM Amps Watts
15K 3.14 38.5 (note the lower RPM starting point)
20K 4.21 51.5
25K 6.80 82.6
30K 9.94 119.8
35K 16.02 136.2

Now time for Data Analysis............................

Hummmmmmmmmm, maybe that $100 quad brushless set up for a FE may be possible after all?

Attached Files

**Jeff Wohlt** · 12-22-2010, 05:24 PM

Killer stuff, Joe!!

**questtek** · 12-22-2010, 08:46 PM

Originally posted by Jeff Wohlt

Killer stuff, Joe!!

Thanks Jeff.

I am including another video of a test I conducted this afternoon. It is a NO-LOAD test using 4 Brand New Leopard 4074 motors and a single 180 A Seaking ESC. NATURALLY THE SEAKING WOULD NEVER HOPE TO POWER 4 OF THESE MOTORS UNDER LOAD, PROBABLY NOT EVEN TWO REALISTICALLY, but I wanted to see if the motors could operate in such a condition and what the current, vs rps curve would be for the following configurations:
1 motor 1 ESC,
2 motors 1 esc
3 motors 1 ESC
4 motors 1 ESC

Here is the link to that video...............

http://www.youtube.com/watch?v=8RU-kblpYeU

**sailr** · 12-23-2010, 12:48 PM

I must commend you for your testing. I addressed this idea with one of the best ESC designers in China about 3 years ago. He never found time to pursue it with all the other projects he had. He said it was possible but starts and/or restarts of multiple motors would be an issue because they would get out of synch between the esc and one or more of the motors. He intended to address that issue using a different method I won't go into here because it's a bit of a trade secret.

One of these days, time and $$$ permitting, we will revisit it and come out with a modular system that solves all these issue.

In the meantime, great job!!!

**questtek** · 12-23-2010, 12:57 PM

Originally posted by sailr

I must commend you for your testing. I addressed this idea with one of the best ESC designers in China about 3 years ago. He never found time to pursue it with all the other projects he had. He said it was possible but starts and/or restarts of multiple motors would be an issue because they would get out of synch between the esc and one or more of the motors. He intended to address that issue using a different method I won't go into here because it's a bit of a trade secret.

One of these days, time and $$$ permitting, we will revisit it and come out with a modular system that solves all these issue.

In the meantime, great job!!!

Thanks for the words of encouragement. Also, thanks for sending out my recent order from you on drive flex shafts for some of your mini-FE's. Great service so, thanks again for filling the order so promptly.

In terms of sync of the motors, you will find this next video VERY interesting. I use inexpensive brushless outrunner motors in LOADED conditions (using matched airplane props). The up-shot is that the motors sinks up perfectly 10 out of 10 (or more) times. when both run in the same direction. However when I run one CW and the other CCW on one ESC they only sync up about 80% of the time. This may be due to the fact that since I only have two CW props and one motor is running CCW the loading factor is radically different. (This is just my possible explanation)

Here is the video using two LOADED inexpensive brushless motors with one ESC...

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

**questtek** · 12-23-2010, 11:28 PM

The comparison tests of two small Turnigy outrunners running on one ESC and that of a single Turnigy outrunner running on one ESC are finished and the results are quite interesting......and to me shocking.
All testing was done under motor loading with 6x4e propellor.

Here are the results based on repeated tests:
1. There is over double the efficiency for two motors and one ESC VS one motor and one ESC. Specifically my measurement for comparison was grams of thrust per Watt of input.
Test Overview:
For the two motor 1 ESC configuration I measured total amps and volts for a wide range of RPM's (12,000 to 19,000) using my Eagle Tree V3 Data Logger. Thrust, in grams, was measured directly from the calibrated digital scale. The same method was used for the 1 motor 1 ESC test configuration.

THE 2 MOTOR 1 ESC CONFIGURATION PRODUCED 2.06 TO 2.72 GRAMS OF THRUST PER WATT OF INPUT POWER. (RPM range: 12,000-19,000, Watt range 230 to 640, Thrust range 627 to 1321 grams)

THE 1 MOTOR 1 ESC CONFIGURATION PRODUCED 0.7 TO 1.2 GRAMS OF THRUST PER WATT OF INPUT POWER. (RPM range: 12,000-22,000, Watt range: 76.5 to 439.6, Thrust range 75 to 358 grams)

So that anyone can draw their own conclusions and manipulate the data from the actual load tests. I have included a complete video of the test comparisons to make this possible at:

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

(sorry, in the video there is about a 15 sec segment in the middle of the video that was accidently duplicated...just ignore this duplication)

I have also included a graph of the results plotting Thrust (in grams) VS Watt Input for all the tests. The linearity of the test data and the enhanced efficiency using the 2 motor 1 ESC configuration can easily be seen.

Comments, Please............

Attached Files

Data Graph 006.JPG (141.5 KB, 11 views)

**m4a1usr** · 12-24-2010, 12:01 AM

Why did you use the upper to mid 1/3 band of the RPM range for your measurements? Wouldnt the data be more indicative of power consumption over the entire RPM band? I'm not surprised by your results since your amperage draw was substantially higher for the higher thrust results with the two motor test. You dont get something without paying a price (more battery power used) and you begin each test at 12k. Was the tool for measuring thrust not able to gauge below 12k?

John

**keithbradley** · 12-24-2010, 12:27 AM

So at 12,000RPM, a single prop makes 75grams of thrust, but 2 props make 627grams of thrust? Something doesnt make sense with the trust numbers...how are 2 props making more than twice the thrust?

I dont see how this is a comparison of efficiancy of 2 motors on 1 esc vs. 1 motor per esc...you are testing the efficiancy of 2 props vs. 1...
Why not test
2 props/2 motors/1esc
vs.
2 props/2 motors/2 escs
Then analize the wattage used. That would be a better test of efficiency. I would also monitor motor heat for both tests, that should also give you an idea of efficiancy. Either way Im not sure why 2 props are making 4X more thrust at the higher RPM range of the test and even more at the lower end. There is no compounding going on there...something doesnt make sense...

**keithbradley** · 12-24-2010, 12:45 AM

Ahh...I watched the video and a couple of things became apparent.
First, I think you would have much more accurate results measuring the actual thrust of the props rather than the lift created. The dual motor rig has the props out to the sides, where as the single motor rig has the prop in the center with the scale directly below it. The difference in available area behind the prop can have a drastic difference on the lift created. I think you should try a rig more like this where the thrust is measured at the scale rather than trying to lift an object off of it:

http://www.youtube.com/watch?v=I2WIqmDrJik

I respect what you are doing and Im not trying to bash your work. Just giving my thoughts, as I am under the impression that you are looking for input.

**questtek** · 12-24-2010, 01:07 AM

Originally posted by m4a1usr

Why did you use the upper to mid 1/3 band of the RPM range for your measurements? Wouldnt the data be more indicative of power consumption over the entire RPM band? I'm not surprised by your results since your amperage draw was substantially higher for the higher thrust results with the two motor test. You dont get something without paying a price (more battery power used) and you begin each test at 12k. Was the tool for measuring thrust not able to gauge below 12k?

John

It was hard to set the RPM much lower actually. In an FE situation you rarely run at the low 1/3rd end of the RPM curve. SO, about 10K RPM was my starting point. The upper RPM point was dictated in the 2 Motor 1 esc set up by the Max power. If you look at the tests at around 18K to 19K I was pulling up to 57 Amps on the small motor producing 639 watts....(Remember, the motor is rated for only 600 watts max.) Uniquely the motors did not really get hot but I never bothered to measure the temps.

You can hear the sound at 19K to 20K RPM and it is quite loud and, even with the Lexan shield I made, I was not all together comfortable to go much higher .

In any case you can just extrapolate from the curves in the graph I attached. Note how linear and repeatable the tests were. You can even see the variation between the two different Turnigy outrunners when running in the 1 motor 1 ESC configuration.

In terms of "more battery power used" please remember the measure of comparison is grams of Thrust PER WATT OF POWER. This means we are comparing performance (Thrust in this case) with the actual Volts x Amps being sucked from the 3S LiPo.