Futaba GY-240 + GWS v-tail mixer = servo jitter

[iter]

There has been some discussion of gyro and v-tail mixer combinations in this forum. I tried one such combination, and need advice.

I'm building a CH-47-type inline helicopter from GWS Dragonfly parts. Rudder and aileron are on a v-tail mixer that goes to front and rear aileron servos. Throttle and elevator are on another v-tail mixer that goes to front and rear ESCs. Both mixers are hardware units in the model--not software mixes on the TX. Both mixers are made by GWS. I tired to add a Futaba gyro in the rudder channel, and I get siginificant jitter on all channels (including the throttles).

1) This is a known-good gyro that has flown in a Shogun.
2) If I bypass the gyro and plug mixer into RX, jitter goes away.
3) If I bypass the mixer and plug a servo directly into gyro, jitter goes away.
4) I tried this with both GWS and Hitec RXs with identical results.
5) Adjusting gyro gain makes no difference.
6) Switching HH mode on or off makes no difference.

The only explanation I can think of is that the gyro may send PPM at a different rate than the mixer and they somehow interfere with each other. This theory does not explain why there is also jitter in the other channels.

Any thoughts on what could be causing this, and how to fix it?

Ari.

[BigS]

It's to do with the output frame not being in sync with the input on the futabe gyros, you could try the telebee/align 400 gyro as this does work without jitter. I'm not sure if heading hold will have enough delay built into it for your application though.

Shannon.

[rdresch]

Check out Model Tech products. They have several mixers that are specially setup for your use. The TH-1 is pretty cheap also. No other mixers required. We need a real electronics Guru to step in here and educate us. Many of the VTOL designs require mixers and gyros. What are the do and do nots here?
Rudy

[v22chap]

Shanon is right ,,you might try a GWS cheap gyro or some other one ..HH any of them will not work I am pretty sure.My tandem dragonfly uses MS micro gyro's and it told you in the instructions to use the cheap piezo's.
By the way the project is looking good.
Keep up the good work,and good luck
Larry

[iter]

Thanks for the suggestions. I don't think I can use the TH-1 though beause it appears to use 120-degree CCPM, while I have fixed-pitch Mini-Dragonfly heads.

Ari.

[v22chap]

The new TH-2 GP will be programable and probably could be set to do the fixed pitch deal .It will also be able to do 4 servo ccpm which could simulate the fixed pitch. by just setting the pitch servo atv to 0 on the TH... maybe What do you think Rudy ??? .I will run this by Joe and see what could be done for you.
Larry

[rdresch]

Not sure about TH-1 but the TH-2 will dothe job.
Rudy

[rdresch]

Sorry Larry posted seconds before I did. I think the TH-2 will work fine. Just set it up as SW1 then use ail to ail for roll and elev to elev servo for pitch (nose up and down) send pitch output from the TH-2 to ESC's and there you go! Strictly my opinion here but I see no reason it won't work.
TH-2 doesn't care if it outputs to a servo or ESC. It supports many swashplate types. Joe, care to chime in.
Rudy

[shooshoo]

I had the same problem and solved it with trading out the 240 with a gws gyro.

[rdresch]

Which one?
Rudy

[shooshoo]

gws gw-03

Hope it helps.

Shawn

[rdresch]

Yup, Thanks

[Lemmiwinks]

There has been some discussion of gyro and v-tail mixer combinations in this forum. I tried one such combination, and need advice.

I'm building a CH-47-type inline helicopter from GWS Dragonfly parts. Rudder and aileron are on a v-tail mixer that goes to front and rear aileron servos. Throttle and elevator are on another v-tail mixer that goes to front and rear ESCs. Both mixers are hardware units in the model--not software mixes on the TX. Both mixers are made by GWS. I tired to add a Futaba gyro in the rudder channel, and I get siginificant jitter on all channels (including the throttles).

1) This is a known-good gyro that has flown in a Shogun.
2) If I bypass the gyro and plug mixer into RX, jitter goes away.
3) If I bypass the mixer and plug a servo directly into gyro, jitter goes away.
4) I tried this with both GWS and Hitec RXs with identical results.
5) Adjusting gyro gain makes no difference.
6) Switching HH mode on or off makes no difference.

The only explanation I can think of is that the gyro may send PPM at a different rate than the mixer and they somehow interfere with each other. This theory does not explain why there is also jitter in the other channels.

Any thoughts on what could be causing this, and how to fix it?

Ari.
You are on the right track. Although it works fine with the pg-03 gyro, the GWS mixer will not work properly with a gyro that is not based on the standard frame rate of ~ 50 hz. The GY-240 uses a frame rate of 70 hz. I got around this problem by purchasing the Omni mixer from Veetail products. It is a very well made for ~$35. I was able to hook up both a GWS rate gyro and CSM 200 HH to the same Omni and it works perfect. Or you can buy one of the old CSM360s gyros which can be programmed for different frame rates.

[iter]

Thanks Dave. I think I'll try the Veetail mixer - although it costs almost as much as a GWS gyro :=)

Ari.

[Lemmiwinks]

With all the the OMNI can do, you may be surprised that it's only $35.....

[iter]

Oh, the list of features is very impressive, it's just that I would have settled for much less in this application :=)

Ari.