Engines sync.

[Fred Arsonneau]

Do you know how to build a device to synchronize two (fuel) engines, to be sure there is no power difference, whatever is the throttle position ?

Fred

[vintage1]

Not easy - need a tacho on each one and a fair bit of software.
Could be done though.

[AndyOne]

Fred,

I have heard thet there are devices available to regulate the rotor speed of a heli, could you use two of these to regulate the speed of each engine via individual throttle servos.

Andy.

[Fred Arsonneau]

Yes, maybe ; but I'm not sure it would be enough, as the device has to compare both speeds, and to reduce the fastest engine throttle down to the slowest one (preferable to do that than to try to increase the slow one, which could be incorrectly adjusted, with the risk of stalling). Then there is a need for a safety mode or something like that, to be able to react correctly and to keep some power in case of one engine stops... Many things to think about !

[AndyOne]

Fred,

The rotor speed regulator, as far as I know not being a heli flier, holds the speed constant to a preset servo position, therefore, you would not need to lock the two engines to eachother, just make sure that the the regulators were set the same.

Andy.

[mike50]

Do you know how to build a device to synchronize two (fuel) engines, to be sure there is no power difference, whatever is the throttle position ?

Fred

You might take a look at the engine sync system available from EMS/Jomar

http://www.emsjomar.com/SearchResult.aspx?CategoryID=6

[Andy W]

Fly electric! :)

[Fred Arsonneau]

You might take a look at the engine sync system available from EMS/Jomar

http://www.emsjomar.com/SearchResult.aspx?CategoryID=6

It seems this is exactly what I am looking for !
I was surprised nobody had already imagined such a system. Anyway the helicopter speed control device could also work ; I'm going to think about every solution

Has anybody experimented one of these devices ?

Thanks a lot
Fred

[TugBoat]

Fred,

I don't know if you got my PM about this.

The EMS/Jomar product has (in my opinion) two issue that you need to consider:

- The RPM sensing is via magnets
- My understanding of the master/slave arrangement is that the slave tracks the master and that there are some failure modes (eg. slave motor fails, slave motor poorly tuned) that do not work 'nicely'.

This is based on information given to me 2nd hand - so you should do your own research.

Tim

[Fred Arsonneau]

Fred,

I don't know if you got my PM about this.

The EMS/Jomar product has (in my opinion) two issue that you need to consider:

- The RPM sensing is via magnets
- My understanding of the master/slave arrangement is that the slave tracks the master and that there are some failure modes (eg. slave motor fails, slave motor poorly tuned) that do not work 'nicely'.

This is based on information given to me 2nd hand - so you should do your own research.

Tim

OK Tim, I was just also wondering what were the failure modes, and if there was any way to desactivate the system in flight (for instance, if the master engine stalls, it could be better to keep the other one running, if there is enough speed). So your information is useful, and I'll keep on investigating. Magnet could also be difficult to set (why don't they ise optical sensing ?)

Thanks
Fred

[TugBoat]

Optical sensing for this application is actually quite difficult to achieve (as I found out) - however it is possible, but quite a bit more complex in the software.

The unit I designed detects engine stalled (on either engine) and drops the other engine immediately to idle - this allows the pilot to realise what has happened before the plane spins into the ground. You can then re-apply power on the remaining engine to keep the plane flying. The unit also has remote engage/disengage facility.

Tim

[Fred Arsonneau]

The unit I designed detects engine stalled (on either engine) and drops the other engine immediately to idle - this allows the pilot to realise what has happened before the plane spins into the ground. You can then re-apply power on the remaining engine to keep the plane flying. The unit also has remote engage/disengage facility.

Tim

So, Tim, did you design your own unit ? I would be interested to build one. (I'm an electronic engineer, but a bit timeless to imagine devices like that...)

Thanks !
Fred

[OmegaDot]

Opto sensors have a hard time in bright or varying sunlight, even with automatic gain and differentiating the signal (to eliminate average light level). Ring magnets and magnetoresistive sensors work very very well.

[Gary Warner]

Fred,

Is this about keeping the 'exact' same RPM's on each motor or more about engine-out safety? Does one concern weigh more than the other?

Without getting into PLL (Phase Locked Loop) circuits (read: headache), one could just detect an engine out failure and program the responses accordingly.

Gary
--

[Fred Arsonneau]

Gary,
No, I was thinking of a device allowing to keep more or less the same RPM's for each engine. It seems that my DC3 crash is likely due to a rather small power difference between the 2 motors. But I know this is a vey complex topic, as there are a lot of chances that the system will be unstable.
Fred

[Gary Warner]

Gary,
...But I know this is a vey complex topic, as there are a lot of chances that the system will be unstable.
Fred

You bet. Throw physics into any feedback system and stability raises it's ugly head. But as in most things, work hard enough (or smart enough) and all things are possible.

Gary
--

[bderksen]

The unit I designed detects engine stalled (on either engine) and drops the other engine immediately to idle ...
The unit also has remote engage/disengage facility.

Tim
Tim:

Sounds very interesting. I would also be interested in building one. Can you supply a little more info on yours?

Bill

[Fred Arsonneau]

I will dig a little bit into Tugboat's design. This could be a very interesting device, but some some aspects have still to be considered. I'll let you know my mind, but maybe Tugboat could send you the necessary information to build one, as he did with me.

Fred

[bderksen]

Tim:
Thanks for the PM.

Fred:
I consider myself fairly handy with a soldering iron, but designing/perfecting something like this is well over my head, so I'll have to wait for you gents to finalize it...
Please keep us posted.

good luck
Bill

[Gary Warner]

Fred,

After yesterdays test flights of my Yaw/Slip/Skid project (http://www.rcgroups.com/forums/showthread.php?t=354497) I'm sure that it would help you greatly in insuring safe one engine out conditions. It will also address mixed levels of power.

Watch for my release of a kit or RTF version in the weeks to come.

Gary
--

[derailed]

fred
what about sycronizers mechanics use on motorcycles?
on a twin cylinder with two carbs, they must be sycronized so one doesn't run too lean or rich

[Fred Arsonneau]

The problem is different. On a twin cylinder engines, there is only... one engine !
So both pistons acts on the same crakshaft. But you are right, both carbs must be equally rich. But this is only done by initial adjustment.
In a bi-motor plane, the difficulty is to get both motors running at the same speed, so thrusts are equal (just a problem of balance). This is still more complex than to get a correct adjustment of both carbs.

[derailed]

ok
it was just a thought
i'm not a mechanic so i need to think harder
lol
i'm planning to build a twin engined plane useing two trimmer engines
hadn't concidered the syncro problems
i'm planning to build a CL-215 water bomber
should be quite a big plane powered by 2 30cc engines

[bderksen]

Fred, Tim:

Any updates?

Cheers
Bill

[Fred Arsonneau]

Fred, Tim:

Any updates?

Cheers
Bill
Bill : not yet

Tim : I've got new information concerning speed sensing hardware, with a much easier detection system (based on artificial lighting of the propeller with a LED, supplied by an oscillator, and a special module which detects the frequency of the reflected light, so the overall detection is much more reliable than with use of natural light)
More to come soon

Fred