spektrum dsp75

[blahblah9]

i crashed my blade400 last weekend, and got it rebuilt the other day, but i stripped out a couple gears in stock servo. my lhs didn't have any gears for them, but he had eflight s75, but he said i should get the spektrum dsp75 to put on my tail, that it would hold it better. so i put it on, and i reversed the rudder in tx, on the gyro and changed it to digital on the gyro. but it seems the tail wags very badly and then i get it down to where it won't hold the tail and all of a sudden it will just turn about 1/4 of a turn on its own, i'll move it back and about 30secs to a min. it will all of a sudden turn about the same much on its own, very quickly too. not a slow moving turn either but very fast and scary for a newb that just crashed LOL.

i didn't reverse the gryo in the tx, was i suppose to do that too? i put on and extra eflight s75 and it holds just like it did right out of box. any tips or could it be bad servo?

[Wolfpackin]

Here's a Scooby snack for ya.;)

I could not get back on the other forum.

I posted this on another forum site recently. It does not address your question directly but another similar one:

Regarding the gyro, I would say it's not great but there are some things you can do to make it hold pretty well. Certainly the GY401 or LogicTech 2000T are much better. But if you can fly the tail a little it's workable.

First you will want to go with a different tail servo. I chose the inexpensive Spektrum DSP75 ($20) just to see if it made a difference and it did. It is very similar to the DS75 that comes stock but it can accept the gyro's digital pulse and the stock servo cannot. So the gyro can then be set to digital mode. A better, tail rudder specific servo, would be even better. I will probably try the Futaba S3154 down the road and the S9650 or S9257 are even better but weigh substancially more relatively speaking.

Then you should move the tail servo ball link to the middle hole, on the DS75 or DSP75. This will increase the gyro/servo resolution, prevent binding and enable the gyro gain to be set higher. On other servos you should position the ball as close the base of the servo arm as possible while still having a straight shot with the pushrod.

Finally, contrary to the manual literature, the position of the gyro's physical gain pot does make a difference. Myself and others have found that setting the pot full clockwise to 100% greatly increases the gyro's holding capability. Doing so was the only way that I was able to get the tail to hold steady with no drift.

After doing these things the tail should be setup mechanically in Rate mode, for no drift or close, and then tweaked after switching to HH mode.
I found that my gyro worked best after getting the servo arm as close as possible to 90d mechanically and then using subtrim to get it exactly straight up.
I got it close to no drift in Rate mode then switched to HH and found it needed another 1/2 turn on the pushrod linkage to get it even closer.
Then I needed to reduce the subtrim I added, to get the servo arm straight, by one click to get the setup spot on.

Is this setup as good as the above mentioned top of the line servos? No, it is not. But it's pretty darn good without having to spend the extra $100+.

I hope that is helpful, good luck.

[blahblah9]

when u put on the spektrum servo for the tail, i know you switched the gyro to digital, did you reverse it using the switch on the gyro or in the tx, or do i need to reverse both?

[Wolfpackin]

I reversed the switch on the gyro and the rudder channel in the Reverse menu in the TX .
Do not reverse the gyro channel in the Reverse menu.

[Wolfpackin]

I just checked for you.

In the TX I have both Gyro and Rudder set to Normal and on the gyro the switch is set to Reverse.

Don't forget to check the stick input response and the gyro's response when you yaw the heli before flying.

[blahblah9]

okay i guess that wasn't the problem then. i guess i'll use the eflight servo for now since i got it put back on. seems like when i had it at 59% then it would do the crazy turning on its on, but if i got over 60% it start to wag. but i hadn't tried to get everything set up in rate mode though. when setting up rate mode, i get to a percent where it wags and then back it off? and if it wants to turn one way or another it means i need to adjust the tail link? then i go to hh mode after getting rate holding pretty good

[Wolfpackin]

Yes.

I found the gyro works better with some subtrim even though that's not usually recommended with other gyros.

Get it close in Rate mode then switch to HH.
If you have a fast drift adjust the linkage length, if the drift is minor use subtrim.
Subtrim with these gyro is usually used to stop any servo/gyro creep but I found it to creep differently in flight than on the bench.
So I just added a small amount of subtrim to correct the creep/drift that was noticable during flight.

Watch the Finless video here on Telebee Piezo Gyros and Similar Gyros.
It's in the Finless Bob's Helifreak Tech Room under Heli Skills and Setup 101.