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Old 08-18-2011, 01:08 PM   #1
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Default Twin Motor Synchronization

I am building a twin electric plane and have some issues with motor speed synchronization. I have tried previous setups I used for twins and they don't resolve the issue. At low throttle settings the motors are as much as 1000 RPM different. I have the same motors, ESCs and batteries for each and have even tried a Y adapter from the throttle channel on the receiver. the setup is one battery and ESC for each motor. (Hyperion motors and Dualsky ECSs - neither are cheap).

I have a Futaba 9C radio that has a Throttle-Needle function that is suppose to allow you to power two "throttle servos" to allow tuning of twin setups. I cannot get it to work with my electric motors. When a motor is plugged into channel 8, it just beeps continuously.

Anyone used this function on electric motors OR have suggestions for tuning the twin motor setup?

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Old 08-18-2011, 01:59 PM   #2
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I have only done one multi engine so have limited expereince, but it seems like most of the posts I have seen try to use one battery to ensure that the each ESC sees identical voltage. Any slight difference in input volts to the ESXC will result in a RPM difference, higher kV motors will make this more pronounced.
You might try a test rig running both motor system from one power source to see if the issue goes away to see if that is the problem.
If it is maybe one of the Futaba users has an idea how to trim it out, but triming it out may end up being difficult unless you can make sure that the battery voltages will always be the same with respect to each other.

The one setup I did was a B17, 4 motors, 4 10 a ESC, one3s 2200 battery. Used a Y connections to take all ESC to the throttle port, seperate UBEC
Good luck with it
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Old 08-18-2011, 05:51 PM   #3
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Vic it sounds like you don't have channel 8 mixed with channel 3. The constant beeping is a sign the esc is not getting a signal to arm.

3 master, 8 slave. And if they are not running up the same you go in and play with the end points and such to sync them.

Granted the stuff you have is not cheap, but it could still be a manufacturing tolerance condition you are fighting once you get the motors running.

When I die, I want to go like my Grandfather did, in his sleep...... Not screaming like the passengers in his plane.
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Old 08-18-2011, 07:06 PM   #4
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First, add a parallel connection between the batteries so both motors see the same voltage. The chance that two batteries will have the same discharge curve is pretty slim, especially if they're not brand new.

Second, try recalibrating the end points on your ESC. Your ESC instructions should include a procedure for setting throttle endpoints. If that fails, try swapping the ESCs to see if you get a better match. Then I would try a differential mix with the transmitter. You'll probably only be able to match them perfectly at one throttle setting so pick where you want the best match.

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Old 08-18-2011, 07:13 PM   #5
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Originally Posted by iFLYrc_Vic View Post
I am building a twin electric plane and have some issues with motor speed synchronization. I have tried previous setups I used for twins and they don't resolve the issue. At low throttle settings the motors are as much as 1000 RPM different. I have the same motors, ESCs and batteries for each and have even tried a Y adapter from the throttle channel on the receiver. the setup is one battery and ESC for each motor. (Hyperion motors and Dualsky ECSs - neither are cheap).

I have a Futaba 9C radio that has a Throttle-Needle function that is suppose to allow you to power two "throttle servos" to allow tuning of twin setups. I cannot get it to work with my electric motors. When a motor is plugged into channel 8, it just beeps continuously.

Anyone used this function on electric motors OR have suggestions for tuning the twin motor setup?
You may want to see if your motors are really identical. That would be the no load current, no load RPM (Indirectly the KV rating), and winding resistance.

You can take the prop off your two motors, and put two pieces of white tape on the rotating parts of your two motors. Then check the no load current and no load RPM of each motor, using the same ESC and same battery. Make certain your battery has the same voltage during the tests on each motor.

Checking the winding resistance is a bit more involved, and requires the use of two common digital multimeters. How to is covered below:
http://www.wattflyer.com/forums/showthread.php?t=50740

If the no load current and no load RPM is identical, AND the winding resistance is identical, problem would have to be with the ESC's or the two batteries. I use Castle Creations ESC's and Hacker motors, but to this point never tried to use them in a twin.

Hope that helps.

DennyV
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Old 08-18-2011, 10:48 PM   #6
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Default Problem Solved

Well, I don't know if was switching back and forth (NOR to REV) on Ch8, but I got the Throttle-Needle function working. It is just perfect for tuning the twin electric motors. Once it is set up properly, the slave motor (NEEDLE) can be adjusted at several points throughout the full range of the throttle. The master motor is controlled as it normally is and you adjust the slave motor at each point (0%, 25%, 50%, 75% and 100%) to match the speed of the master motor - absolutely the perfect solution for mismatches in the motors or ESCs.

So now I have exactly matched the motor speeds from 2000 RPM up to 7000 (half throttle). I did not have a way to hold down the plane for full throttle matching due to the location of the nacelles. They sounded pretty close so I think I will be OK.

Thanks to all for your help.


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Old 08-18-2011, 10:55 PM   #7
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reallity is , you won't notice if they aren't spot on. even a nitro doesn't have to be perfect.

they need to be reliable... and in the same arena.. if same basic motors,props, batteries are new and charged.. good to go.

if using old batteries.. motors.. then you can get drastic differances.

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Old 08-18-2011, 11:12 PM   #8
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Originally Posted by tampaflyer View Post
reallity is , you won't notice if they aren't spot on. even a nitro doesn't have to be perfect.

they need to be reliable... and in the same arena.. if same basic motors,props, batteries are new and charged.. good to go.

if using old batteries.. motors.. then you can get drastic differances.
I agree they don't need to be perfect but mine were in the 1000 RPM range which was not close enough for me. they are now within 100 RPMs and I am a happy camper. Hope she flies as good as she looks.

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Old 08-18-2011, 11:16 PM   #9
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just rember , it thinks it a jet.. respect it as one. the props push no air over anything. if you stall test, be high it might need time to recover.

put the have great wings and fly smooth.

good luck and get a video

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Old 08-19-2011, 02:20 AM   #10
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Originally Posted by tampaflyer View Post
just rember , it thinks it a jet.. respect it as one. the props push no air over anything. if you stall test, be high it might need time to recover.

put the have great wings and fly smooth.

good luck and get a video
You said " it thinks its a jet, respect it as one". I take it you mean I need to keep the speed up. I plan to fly it relatively fast but not like a jet. From all reports, it lands a little fast but very stable. Have you seen one of these fly?

Thanks for your help. I'll post a maiden report soon.

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Old 08-19-2011, 02:49 AM   #11
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don't try to be too slow on final. lift the nose to induce drag.. like landing a shuttle.. nose up and a click or two of power. it will slow down , but don't be reall slow till you about to land.

i have seen to many people see a prop and think cool that they are like every other prop plane. if you think JET you should avoid most mistakes.

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Old 08-19-2011, 02:57 AM   #12
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this has a similar wing... but uses 2 6 cell 5000mah lipos ... but performace whould be similar... he didn't get the landing.

if you have ever seen a plane begin to rock its wings before a stall? if you see this in a jet.. especially landing... power up and relax on the elevator.

if you are only 5-10 off the ground you may not recover...

i am not trying to scare you.. just go out on the maiden with a plan....

take off..trim.. a pass or two the set up for landing.
check the plane , batteries, heat on the esc/motors (ASAP). then adjust timer as neccesary. sit back take the coodo's the first one's done

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