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Nov 06, 2017, 10:33 PM
Registered User
metalwizard's Avatar
Help!

Twin engine trimming


Ok got a weird question..

I have a Hobbyco Twinstar..

obviously twin engine.

Im using a DX9 (with a 6 channel receiver for now)

I have left throttle on channel one controlled by throttle stick
I have right Throttle on channel six (aux1) controlled by throttle stick.

NOW I can trim the two engines on the bench by using the servo travel and trim to get them synced up pretty good.

just a thought/idea is there any way I can program the Know on the dx9 to trim them ?? you know motors dont always run the same it would be nice to have an easy way to trim them slightly in the air.. to get rid of the harmonics at any speed. just turn the know or even one of the back trim sliders..

if anyone has a way to program something like that in that would be AWESOME

thanks
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Nov 07, 2017, 07:22 AM
Registered User
Rotten40851's Avatar
I have been flying twins for quite a while now, I have 2 Twinstars ( Both with OS FP 40's one converted to a high wing with floats I call "The TwinSea") a TF Cessna 310 and a twin Otter at the moment. You are on the correct path by having the engines on separate channels and trims, I like to put a small number behing the nacelle determaining which engine is on which channel and trim, And all I can say is Please don't concern yourself with syncing too much, With twin engine ICE ( Internal Combustion Engine) aircraft syncing is desired but not crucial. Here is what I suggest. Starting with one engine, start it and get it running peak. Shut it down and do the same to the other. Then Tack both engines and see the difference between them Id you are within 600-1000 rpm's leave them If they are out of that range trim the higher RPM'ed engine down to the lower one. With twins it is about reliability. Yes we all want that beautiful synching sound but not at the cost of the model. I have spent countless hours trying to sync perfectly only to experience engine failure due to overheat and such. Don't sweat the RPM difference too much , let your engines work easy independently and not one trying to keep up with the other by straining itself, Hope this helps, Rotten
Nov 07, 2017, 09:09 AM
A man with a plan
Balsaworkbench's Avatar
Generally the idea is that you're not supposed to worry about it. Tune independently, then synchronize the idle and cutoff settings. Don't worry about the top end. At top speed you have enough airspeed to counteract an out of sync condition.

This was done on one channel before fancy radios were invented, and it worked. I'm not telling you to do it with one channel. I'm just telling you that if you're using two channels your goal is to get the engines to idle and run at the same time rather than worry about the top end. If you have total travel volume adjustments available, use them to get a pleasing sound at full throttle, but other than that, concentrate on the other end.
Nov 07, 2017, 09:22 AM
Me Likey Scale Planes
scale_only's Avatar
Quote:
Originally Posted by metalwizard
Ok got a weird question..

I have a Hobbyco Twinstar..

obviously twin engine.

Im using a DX9 (with a 6 channel receiver for now)

I have left throttle on channel one controlled by throttle stick
I have right Throttle on channel six (aux1) controlled by throttle stick.

NOW I can trim the two engines on the bench by using the servo travel and trim to get them synced up pretty good.

just a thought/idea is there any way I can program the Know on the dx9 to trim them ?? you know motors dont always run the same it would be nice to have an easy way to trim them slightly in the air.. to get rid of the harmonics at any speed. just turn the know or even one of the back trim sliders..

if anyone has a way to program something like that in that would be AWESOME

thanks
Not sure how the mixing works with Spek, so this may be of no help at all,,, but to achieve what you want with my Futaba 10c, I'd build a "mix" throttle (master) to aux-1 (slave), then assign function to a knob or slider, both will still move with throttle stick,, but the knob will move the servo and change where it centers and it's end points,,,

This may move the aux throttle to much at each click point to fine tune,, worth a try though

good luck
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Nov 07, 2017, 10:34 AM
Registered User
I have a Twin Star also with two Os Max 40's and have tried to sync them. I learned and agree that staying with 600- 1000 rpm is the best way. One think about the Twin Star it is one of the best twins that will fly well on one engine. Getting it down when a engine flames out on one engine is no problem. It is a shame this twin is no longer made. I have two and plan on recovering the one I bought from a club member who parted with it.

Smooth & Strong Signal
Ron
Last edited by RTLIKES RC; Nov 07, 2017 at 10:35 AM. Reason: Spelling
Nov 07, 2017, 10:59 AM
Registered User
metalwizard's Avatar
Thanks for the input.


they actually both run pretty good on the ground and getting them to "sync" at full throttle seems to be easy on the ground..

I was just curious if there was a way to do a little timming more for SOUND in the air.. you know the harmonic you get when two are slightly out of sinyc.. I figured it might be an easy trim in the air..

oh well ill give it a try and see what happens I have been wanting one of these for a long time.. had one in my cart then went back to buy it and the were discontinued.. so I bought a used one here..

I notice on Tower hobbies they have all the parts for them the ones out of stock say DUE november... I wonder if they are doing a re release??
Nov 07, 2017, 11:12 AM
Registered User
I've done what you want to do on a twinstar. Mark the spot on the knob where it runs good, you need a reference point. I didn't do that and the engines got so far out of sync I had to go to idle and land. If you run into trouble, you can get back to your starting point. I stopped doing that cause it was too much trouble.
Edwin
Nov 07, 2017, 11:34 AM
Registered User
metalwizard's Avatar
Ok but how do you set it up on a dx9 to do that
Nov 07, 2017, 11:01 PM
Registered User
It was back in the 72mhz days and on a Futaba. On my DX18 I use a mix for rudder and tail gear steering and the knob is used for fine tuning the steering on my big multis. Takes two mixes. Mix1 is rudder to aux2 (tail gear steering), 100%, on. Mix2 is knob to aux2, 100%, on. Use primary throttle instead of rudder and second throttle instead of tail gear steering and that should work. Knob will only affect second throttle. Don't forget to mark your reference and which direction increases rpm. Up in the air, it's difficult to figure out what's going on.
Edwin
Nov 08, 2017, 07:31 PM
Registered User
metalwizard's Avatar
Quote:
Originally Posted by edwin1
It was back in the 72mhz days and on a Futaba. On my DX18 I use a mix for rudder and tail gear steering and the knob is used for fine tuning the steering on my big multis. Takes two mixes. Mix1 is rudder to aux2 (tail gear steering), 100%, on. Mix2 is knob to aux2, 100%, on. Use primary throttle instead of rudder and second throttle instead of tail gear steering and that should work. Knob will only affect second throttle. Don't forget to mark your reference and which direction increases rpm. Up in the air, it's difficult to figure out what's going on.
Edwin



Awesome thanks
Nov 09, 2017, 07:47 PM
Registered User
I mix the throttle channel to Aux 3 for the second engine. Since Aux 3 is controlled by the R knob, turning the knob trims the slave engine. Since you only have a 6 channel receiver, you should be able to map Aux 3 to the channel 6 port on your receiver using "RX port assignment" in the system setup menu.

Also, as stated above, run the engines individually for best performance/reliability not to get them synced. I tune each individually, than use the "Balance" function under "Servo setup" as a sort of throttle curve for each channel to get the RPM's close at any given throttle position and limit the strong engine to match the weak at full throttle.

Jeff
Last edited by 2ltime; Nov 09, 2017 at 07:58 PM.
Nov 10, 2017, 06:35 AM
Registered User
Rotten40851's Avatar
Pics of the TwinSea (Twinsy)
Nov 10, 2017, 06:36 AM
Registered User
Rotten40851's Avatar
Painted floats
Nov 12, 2017, 01:39 PM
Registered User
metalwizard's Avatar
OH MAN the twin on floats looks AWESOME... now you have me thinking... I already have a st of 40 size floats looking for a home..
Nov 13, 2017, 04:55 AM
Registered User
Rotten40851's Avatar
Thanks, it flies great, the 2 OS FP 40's pull it around nicely


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