Two Brushless motors on One ESC….YES!

[m4a1usr]

In terms of "more battery mower 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.

Yes. I understand you are defining a unit to measure force. Do you have a copy of "Brushless Permanent Magnet Motor Design" by Dr. Duane Hanselman? Not that you need it Joe, I was just curious as it is very informative for what you are doing currently. Many usefull formulas applicable to our hobby.

John

[TotalPackage]

where can you pick up that book ?

[TotalPackage]

Whoever said that the two would be less efficient they are right coz the motors are not gonna match exactly but you would think handwound motors that are measured could be closely matched?I mean that mistmatch inefficiency applies to the batteries not exactly matching as well right?

[m4a1usr]

where can you pick up that book ?

You can find it on Amazon but here is a link for sections or chapters. http://www.eece.maine.edu/motor/ It is spendy! The book goes for $175 so not many people own one out of their own pocket. I got lucky and inherited one from work when one of my co-workers retired. The guy is a genious at Matlab applications. Wish I had him as a consultant 5 years ago! Have since systematically been changing everything over to Labview since they are dominating the market and buying all the little guys out. Oh well. You gatta love National Instruments!


John

[questtek]

Yes. I understand you are defining a unit to measure force. Do you have a copy of "Brushless Permanent Magnet Motor Design" by Dr. Duane Hanselman? Not that you need it Joe, I was just curious as it is very informative for what you are doing currently. Many usefull formulas applicable to our hobby.

John

Thanks for the tip. I can use all the help I can get since I am in no way a motor expert but more like a slight cut above a novice. I am just trying to use them effectively in several projects and the tests are designed to find out how best to do this I will try to get of a copy of the book you recommend. I am sure it would be beneficial to me. Thanks again,

I also found a great program for Scorpion motors for evaluation. Although I am not using their specific motors, the computer program I think will help provide some guidelines. Unfortunately there is nothing on multiple motors with one ESC. Most, probably like me before the testing, thought this could never be done.
Maybe it still cannot effectively but right now that appears to be not what my test results are indicating. This is why I felt I had to include the actual test video so people did not think the data was pure vapor ware.

[m4a1usr]

At this point I'm thinking (yea, very dangerous!) you have proven that with one ESC and two motors the IR losses (wasted battery power/heat generated) is halved or something approximate. Worth every moment from my perspective and this is going to only get better.

John

[questtek]

A few posts back SAILR mad this comment........"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."

Possibly these tests I have done may inspire them to look into it on a more serious basis. I keep trying to figure out if I did anything wrong in the tests so I went back to check if everything was in calibration and if the numbers repeated...........they did.

Project continues after Christmas...............and a Merry One to All.

[keithbradley]

No response to my posts? Im curious what you think...

[questtek]

I think when blackcat refered to the higher cost of larger escs, he was refering to escs that are higher current capable than the t-180. The t-180 is kind of an in-between. Compare a Swordfish 120 here at OSE ($69) and a Swordfish 240 ($259). He does have a piont about the more capable escs being considerably more expensive.
Steven had the 200A Swordfish's made for that very reason, but I think that esc (or the t-180) would be well suited for ONE motor like the 4074/2200kv, not two.
If you were going to run a pair of Leopard 4074's (2200kv), you would expect to use a higher Amp esc than 180, right?

I think it would be cool to use one esc if it were the more cost effective choice. I hate all the extra parts. One esc would make things a lot cleaner.

Sorry, I must have missed your post...........First, you are correct, Under high loads the SeaKing 180 is perfectly suited to the Leopard 4074 . I have recorded a high of about 120-140 Amps on my Insane Hydro with large prop on 4S.

However if you would run a milder set up and draw about 100 Amps you might be OK two Leopards on one Seaking. I will be trying this on a Mean Machine I have that is exactly set up like this. It appears that in running two motors you do not double the amps but its more like 70% of the total......at least that is what I have been told. (This is why I love the Eagle Tree and lab testing so I can actually find out)

I am not interested in using expensive ESC's. I am just happy with the $79 Seaking 180 or the $29 Hi Model or Suppro, 200 with my water cooling. The trick for me is to find motor/load combinations that permit me to use these ESC's on affordable multi, brushless motor set-ups.

There is lots of talk using 600 to 1500 watt outrunnrs in multiple motor setups. I believe that FighterCat 57 is doing this. So, theoritically a single $29, 200 AMP ESC just may possibly run 4 of these 600 watt outrunners. I am running two from one of the Seakings with no problem under loaded conditions.

It's easy to experiment with inexpensive components .....and you will notice I have no Castle HV's or multiple Leopard 5092's in my testing! However I just ordered a few of the Castle Creation SALE outrunners and will try them on one ESC.

[keithbradley]

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...

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.

I was refering to these

[FighterCat57]

Yes, having excellent results using mid-large helicopter ourtunners spinning boat props. High Torque and High RPM w/high efficiency.

I have yet to try two motors from one ESC, but if I did, I would try the Suppo 200 and two 3126 outrunners. I would ask the MFR, but I don't want to confuse him any more. He's having enough trouble filling orders accurately.

[antslake]

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.

First of all, great work! Very interesting. I am skeptical about the efficiency of a setup like this, especially when the loads start to vary on the motors.

When doing experiments like this, it is important that they be in as a controlled environment as possible. You are doing a great job. One thing I noticed though that could give this false(possibly) reading of more effceincy is the position of the prop on the stand. When you are using two props, the props backwash is not blowing on the scale that much, and the props have 50% more free space around them. When you use the single prop, the prop is blowing directly on the scale, countering the effect of lift. Here is what I would love to see you do, and you will thank me for this, turn the props around, so they push down. You will have no prop wash on the scale, and the props will not fly off and hit you either, and your family jewels will be much safer

[antslake]

I would also like to see a graph that plots rpm's vs input watts, I think that would be more accurate in determining efficiency. It would be nice to have the same exact voltage in the two tests too. When using the two motors, your voltage drops more, although I am not sure if this has an affect on it or not. But knowing that higher amps and lower volts, is less efficient than the opposite, maybe a factor.
How about using two packs with the two motors(2P), and one pack with the one motor, and maybe the voltages would stay the same. That is another variable you can eliminate. You are comparing twice the amp draw using a single pack. That could have an affect on the numbers.
Just trying to help.

[ManuelW]

Concerning efficiency:

I watched your Video of one Seaking 180 and four Leopards 4074. All the measurements where taken at about 11.000rpm as far as I can see.
Well with four motors the starting of the motors is quite rough, might be a problem to find the right commutation. But most interesting is the amp draw at 11.000rpm:
one motor: 1.38amps
two motors: 6.8amps
three motors: 8.3amps
four motors: >25amps

Doesn't really seem to increase efficiency at all. There has to be a massive error in your measurement equipment concerning thrust I think. Even the step from one motor to two motors shows a massive reduction in efficiency as I expected resulting from small manufacturing differences of each motor.

Best regards,
Manuel

[antslake]

The scale may also not be accurate determining negative numbers. Another reason to turn the props around, and make them thrust down. This is the way I use my Medusa research dyno.