shadeyB
Legendary member
Another thing I’ve been reading after my 2nd twin build
When your extending wires, it’s better to extend your ESC/motor wires = having shorter wire to the battery
Solved Twin Motor Question...?
- Thread starter BATTLEAXE
- Start date
When your extending wires, it’s better to extend your ESC/motor wires = having shorter wire to the battery
BATTLEAXE
Legendary member
At this point i wont be speculating on that. Thanks for the tip though
PsyBorg
Wake up! Time to fly!
Are you sure about that? Longer esc to motor leads would create bigger induction fields that would interfere more with radio gear and FPV as well as possible sync issues. Longer power leads from the battery would be dc and no magnetic fields pulsing. Yes on higher current draws they would heat up but thats due to improper wire gauge usage. Stock wires are meant for shorter runs but that doesnt necessarily mean that longer runs can not be done with properly sized wire for longer distance and current draws on the feed side.
quorneng
Master member
You may have noticed the capacitors on the battery side of an ESC? Why are they there?
The current supplied by the battery is not smooth at all but pulsed as the MOSFETs switch on and off at a high rate. The capacitors are there to provide smoothing to limit the pulsing current creating induction voltage 'spikes' that would kill the voltage sensitive MOSFETS. The longer the battery to ESC wires the greater the chances of creating voltage spikes. The factory fitted capacitor size is set to reduce the spike risk to an acceptable level with the average ESC and battery lead length. If longer battery to ESC wires have to be used additional capacitors can be fitted, ideally at intervals along the wires, to absorb the bigger voltage spikes.
Without this protection significantly extending the battery to ESC leads will increase the chance of an ESC failure in direct proportion to their length.
There is no such problem with long motor leads creating voltage spikes as the motor has no electronics within it. Resistance losses will eventually effect the motor performance but provided the wires have a sufficient cross section to carry the amps the practical limit is measured in tens of metres not centimetres.
The current supplied by the battery is not smooth at all but pulsed as the MOSFETs switch on and off at a high rate. The capacitors are there to provide smoothing to limit the pulsing current creating induction voltage 'spikes' that would kill the voltage sensitive MOSFETS. The longer the battery to ESC wires the greater the chances of creating voltage spikes. The factory fitted capacitor size is set to reduce the spike risk to an acceptable level with the average ESC and battery lead length. If longer battery to ESC wires have to be used additional capacitors can be fitted, ideally at intervals along the wires, to absorb the bigger voltage spikes.
Without this protection significantly extending the battery to ESC leads will increase the chance of an ESC failure in direct proportion to their length.
There is no such problem with long motor leads creating voltage spikes as the motor has no electronics within it. Resistance losses will eventually effect the motor performance but provided the wires have a sufficient cross section to carry the amps the practical limit is measured in tens of metres not centimetres.
bwarz
Master member
Fully agree here - the noise at the DC input to the ESC could be enough to kill it. Extend motor wires not power. Not sure if it would cause weird issues with one motor though? To further an earlier note too - if you use two batteries you should tie the esc power grounds together to prevent the signal ground from trying to pull current to drive a motor in the event of a battery problem on one side - rare sure but could surely bring her down in flames pushing 10-20 amps through that tiny ground wire (although video of this would be cool
) I have read in these forums of another who uses Schottky diodes (low forward voltage drop) on the esc to receiver (via wye) power leads to keep using both becs. The supplies wouldn't 'fight' to supply power - it's just that one would provide more current until its voltage dropped enough to match the other - like two batteries in parallel in a plane. Although the diodes wouldn't be necessary with linear becs...
I've got a B25 mini twin with nothing other than a wye from the escs and haven't had anything odd occur with the motors. Not using differential thrust.
As far as @BATTLEAXE original problem.... I got nuthin anyone else hasn't suggested lol Did you rule out that it wasn't something weird with differential? Disable all differential and see if it still occurs?
L Edge
Master member
Battlaxe
Since you like to explore and resolve issues, I am going to offer you another way to go to get differential thrust that has lots of advantages.
1) Simple to install, no wires to pull out. Just hook it up and that's it.
2) You just use the throttle and rudder channel. No extra channels!!! So if you have a 6 channel radio, you got room for flaps, etc.
3) No mixing program to deal with.
4) With the trim adjustments, you can get both engines to start at the same time. Also, with throttle trim, you can sync your engines in flight.
5) Then go into the rudder expo, and you can adjust the curve to get differential thrust to match your turns.
'Planes I have used it on was my SR-71, transports(works good with EDF's) and even I can hover using it.
What is the answer----- A V-tail mixer or used also as elevons mixer.
How does it work?
The throttle(s) work togeather much like an elevator. Both electronically move up and down. The throttle trim allows you to move the throttle so you can sync the engines in flight.
The rudder(s) work like the ailerons. One side goes up and the other side goes down. So when you move the rudder one way, one motor increases in speed and the other reduces an equal amount. Hence, differential thrust. Adjust the trim, start the motors together.
I use GWS V-tail mixer (have 7 of them) and I can't find a dealer these days. Hobby King carries them for $5.33 and it has 200 step(don't get something less) . If you need to see some videos, glad to show you.
You are an explorer, why don't you try on your next order, get one, and will be glad to walk you thru it. Then you can pass it on to others.
Added;
Elevator goes to throttle rx, aileron goes to rudder rx,
esc leads (left motor-top right motor-bottom)
Since you like to explore and resolve issues, I am going to offer you another way to go to get differential thrust that has lots of advantages.
1) Simple to install, no wires to pull out. Just hook it up and that's it.
2) You just use the throttle and rudder channel. No extra channels!!! So if you have a 6 channel radio, you got room for flaps, etc.
3) No mixing program to deal with.
4) With the trim adjustments, you can get both engines to start at the same time. Also, with throttle trim, you can sync your engines in flight.
5) Then go into the rudder expo, and you can adjust the curve to get differential thrust to match your turns.
'Planes I have used it on was my SR-71, transports(works good with EDF's) and even I can hover using it.
What is the answer----- A V-tail mixer or used also as elevons mixer.
How does it work?
The throttle(s) work togeather much like an elevator. Both electronically move up and down. The throttle trim allows you to move the throttle so you can sync the engines in flight.
The rudder(s) work like the ailerons. One side goes up and the other side goes down. So when you move the rudder one way, one motor increases in speed and the other reduces an equal amount. Hence, differential thrust. Adjust the trim, start the motors together.
I use GWS V-tail mixer (have 7 of them) and I can't find a dealer these days. Hobby King carries them for $5.33 and it has 200 step(don't get something less) . If you need to see some videos, glad to show you.
You are an explorer, why don't you try on your next order, get one, and will be glad to walk you thru it. Then you can pass it on to others.
Added;
Elevator goes to throttle rx, aileron goes to rudder rx,
esc leads (left motor-top right motor-bottom)
Last edited:
tomlogan1
Elite member
I've built several twins and have always used a single battery with the poistive lead removed from one side. I've dabbled with differential thrust but was not impressed and went back to letting the control surfaces handle turning. I wonder, though, if you calibrated the ESCs when you set up the plane? On my first twin I strugled with the motors being synced until I recalibrated the ESCs. So with the potential of the ESCs being not calibrated and differential thrust slowing one motor when you turn, could that be the issue? I realize ESC calibration is something that is elementary, but sometimes overlooked. Hope you resolve your issue.
BATTLEAXE
Legendary member
I did calibrate the ESC's, they were synced. I found my whole issue to be the receiver, It was giving random commands on its own. Last twin I had up it went into a flatspin on its own, better then I could have pulled it off in the first minute of a maiden
quorneng
Master member
Battleaxe
I suspect your issues with the receiver were not directly as a result of it being a twin but from some electrical fault possibly a bad connection. Being a twin a intermittent connection could result in one motor misbehaving which would have much more serious consequences than if it were a single.
I suspect your issues with the receiver were not directly as a result of it being a twin but from some electrical fault possibly a bad connection. Being a twin a intermittent connection could result in one motor misbehaving which would have much more serious consequences than if it were a single.
BATTLEAXE
Legendary member
That's exactly what I found, the only Rx i had was a beat up Storm that I think might have been faulty out of the box. It has been through numerous crashes. In a twin it was nuts, in a single it would just brown out. Got a new Rx and all is good and consistent now, thanks for the response.
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