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Old Jul 16, 2002, 04:06 AM
17 years on RCG!
United States, NV, Las Vegas
Joined Dec 1996
3,119 Posts
Twin brushless motor and ESC problems - how do I get the motors "in sync"

Hey guys!

A few weeks back I purchased a Kyosho Lear Jet, fitted with retracts and twin brushless motors.

The motors are Aveox 1010/2ys, with Castle Creations Dragon 35 ESCs. Although you may have used different brushless motors and ESCs in the past, please read on - I think the problems I have with the motors relates to ALL twin brushless motors and ESCs...

When I received the plane, both ESCs had their Rx leads soldered together. This was to save weight rather than using a "Y" harness. Both ESC/Motors run off of one single 11 cell pack so their power leads are also "Y'ed." I went ahead and bench tested everything before making changes to make sure it all worked - and it did. But, I could only SOMETIMES get the ESCs to arm and run the motors at the same time. Most of the time, one motor would start a click or two on the throttle before the other. At full power there didnt seem to be a difference in power, but its virtually impossible to tell...

Later on I plan to run 2 seperate 12 cell packs so I went ahead and soldered new Rx leads to each ESC and used a common "Y" harness to connect them to the receiver. Same problem - sometimes the motors came up at the same time, many times they did not. Even when the motors do come on at the same time, they dont seem to be producing equal power entirely at lower throttle settings. Anything over 1/4 throttle I just cant tell as the fans are really churning!

So I decided to plug each ESC into the receiver alone - one ESC plugged into the throttle, and the other I plugged into Aux 1. I used my Tx (JR 8103) to mix throttle and Aux 1 and tried it out. Actually, it seemed to work better - more often I could get the motors to start at the same time, but still, there were times they wouldnt start together.

Again at full power, it seems both motors are producing all the power available equally, but I dont know. How can I tell? Is this problem common? Will going to a seperate battery pack for each ESC/motor help? Should I continue to use a "Y" harness on the leads or keep the seperate plug ins with a radio mix in place?

Thanks for all the help guys - I really want to fly this thing! Im only nervous because every time I would throttle back too far, the motors wouldnt restart in the air at the same time. I just want to know if there is any way to overcome this problem at all, or am I stuck with it. I contacted the previous owner who said he flew it like that and he knew it wasnt right on but didnt think it mattered much once in the air. He had a lot of successful flights with it that way, but I want to make it better if possible...

Jason
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Old Jul 16, 2002, 07:58 AM
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Gordon's Avatar
Joined Aug 2000
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Hi Jason

I'm shortly goig to be flying brushless twins myself - twin Actro C6s in an Aeronaut Tigercat, and a pair of Hacker B50-16Ls in a scratch-built Meteor. So I'll be looking out for the problem you just described!

I would think that slight differences in component tolerances within the escs are causing your problem. Setting them up as you have done using 2 mixed channels, and then adjusting the tracking of each channel against the throttle stick is probably your only hope to get the motors synchronised at low and mid-range throttle settings. I don't think you'll be having any problem at max power.

Here are a couple of thoughts, though:

Do the Castle Creations escs have different modes available. For instance, is there a soft-start option available for belt drive? I just wondered if using that setting would help in getting the motors wig-wagging and starting together.

Additionally, if you select brake-off, in the air the fans should stay rotating in the slipstream even without power - unless the Aveoxes have so much cogging that the motors stop quick anyway - though my Pletti brushless Schubi fan decelerates only slowly on cutting the throttle with no brake, and that has loads of cogging.

Cheers

Gordon
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Old Jul 16, 2002, 09:18 AM
Flying Welder Pilot
Plane Crazy's Avatar
Reno, Nevada
Joined Jan 2001
1,137 Posts
I have seen this problem also with the Dragon 35 and Aveox 1010 2Y combo running off one pack and Y receiver cable in a twin application.

I attributed it to the component tolerence differences between the two Sensored Dragon 35 ESCs. It always seemed like one of the ESCs was favored, and the other was starved for power.

When I changed over to senserless Brushless ESCs the problem dissapeared. Running two packs might help solve the problem, but there will probably still be a difference in RPM.

On the Lear the EDF nacelles are close in to the fuselage. I never notice any adverse handling or tracking from minor differences in RPMs from the 2 fans. Other than the Twin Fan sound was not as cool.

GordonM
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Old Jul 16, 2002, 05:21 PM
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Haldor's Avatar
Stavanger, Norway
Joined Feb 2000
7,999 Posts
Dont know the cause but a solution could be a single ESC fopr the two motors. When a succesful start of both motors is done they'll be in perfect sync.
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Old Jul 16, 2002, 10:33 PM
joe
Registered User
greenbay,wi,usa
Joined Apr 2000
412 Posts
using one sensorless speed controller would work mabby
I could never get my two small brushless motors to start at the same time with one controller
it was always hit or miss
if any one knows of a sensorless controller that can start two 010 fans at the same time I would sure apreciate it
mabby it only works on the big boys

Crazy Joe
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Old Jul 16, 2002, 10:58 PM
EDF all the way!
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Gilbert, Az
Joined Jun 1999
7,988 Posts
Twin motor single ESC

I have flown my EJF Rafel for a couple of years using two Astro 4T 05 brushless/sensorless motors and a single 3SL-40-6-16 ESC with no problems. This was using a single 12 cell 2400 ma pack.
Good Luck,
Bob Ruff
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Old Jul 16, 2002, 11:05 PM
York Electronics
Gary Warner's Avatar
Dallas Tx USA
Joined Apr 1999
2,505 Posts
I have twin fans running two brushed motors in series. The motors are as identical as can be. I get the same thing you do. One always starts before the other. Full power they are about 120 rmp out of sync (2 drones per second). I didn't think that was too bad at 21k.
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Old Jul 17, 2002, 05:22 PM
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Las Vegas, NV
Joined Dec 1996
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So Jason did you get to fly the Lear yesterday? I hope it went well.

I wouldn't worry about the motors not starting simultaneously. You probably wont be throttling back or cutting the throttle that much anyway. If there's a one second delay so what, if you are in the air the vertical stab is big enough to overcome any adverse yaw. During takeoff roll corrections can be made with steering if the jet yaws at all.

As you know running both motors on one speed control at 70 amps isn't a great idea for battery longevity. Two seperate packs and controllers like you are planning on using is the way to go.

I hope I get to see this one sometime!
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Old Jul 17, 2002, 06:35 PM
Making Cuisinarts Fly!!!!
Richardson, Texas
Joined Dec 2001
298 Posts
Try disconnecting the BEC and run and RX pack.

I had issues with my dual brushless setup on my Viper Twin.

Also what batteries are you using? Can they provide the current both motors need. My VT was doing all kinds of wierd things when I was testing it on a zagi 1700 pack. Try pulling 50 amps from a 1700au cell. Voltage drops like a rock. Then one motor cut out then the freaked and shut down to a large voltage spike.

Moral of the story......use a rx pack and run the correct capacity batteries.
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