Does anybody know if the Spektrum DSP75 servo will work with the Futaba GY401 gyro in digital mode? There was a comment on Tower Hobbies that said it's not compatible with JR digital servos but I couldn't find anything in the GY401 documentation to back that up.

I wouldn't hook that servo up to that gyro.

JR makes some tail rotor servos, I think its the 8700 or 8900 that go hard over when the 401 initializes.

What are you putting it on that you would be tempted to use that servo?

It's going to go on a trex. I was thinking of putting it on my Blade 400 to try it out until the trex is built. It's got a DSP75 on the tail.

I would reccomend a better servo for the tail.

If you are running the Spectrum DSP75 servo on the tail of a Blade 400 then you are one lucky person. That servo is not compatible with the 400 Blade Gyro in Digital or Analog modes. I tried it and myself, the servo buzzes and jitters. Uopn spool up the tail goes hard over, reduce cyclic and it releases. Spectrum and EFlite both verified the servo should not be used for tail gyro control on the Blade 400. It is fine for the Swash (I am using them now) but reqires all the servos to be replaced as a matched set and they all neeed to be reversed using the programming box only not the radio. End points should be adjusted as well to match the original EFlite servos.

In reality putting a high end servo on the tail of a Blade 400 does little to improve flight performance. The pilot may have more confidence replacing the tail servo but actual performance is little improved. The longevity of a high end servo on the tail of a Blade 400 is not garenteed over the stock units.

My experience, your mileage may vary.

That's interesting as the manual from the 400 states otherwise.

From page 26:

"When the Servo Mode selection switch is set in the Digital Servo (DS) position, the gyro is
optimized for use with digital servos that are designed to accept a pulse rate of 275Hz. Some
such servos include the Spektrum DSP60 and DSP75, as well as the JR 3400G."

I get the buzzing you describe. Everything seems to work during the setup and control check. I did need to reverse the rudder channel and gyro to get proper response. I have not been able to test fly it due to the weather.

Did you notice any difference using them on the swash?

Test flew the 400 today with the DSP75 on the tail with the gyro in digital mode. I did not experience any problems and the tail held very well in HH mode. Rudder channel on the DX7 and gyro reversed to get proper response.

I have a DSP75 on the tail of my Blade 400 as well. It is recommended in the B400 manual if you want to use the stock gyro in digital mode.

When I first powered up with the new DSP75 servo the heli started fast CW piros. Flipped the Norm/Rev switch on the gyro and all was good again. Did not use the servo programmer to set servo to rudder mode.

Yes, Spektrum DSP75 servos will work with Futaba gy401 gyros. The note on the tower hobbies page is in reference to the 8700G servo which is a PCM servo designed to only work with the G7000T gyro. The newer 8900G should work just fine with a gy401 because it uses the standard signaling, but the 8900G has a deadband of zero compared to most digital servos with a deadband of around 3 micro-seconds.

The Spektrum DSP75 can handle the high frame rate from the gyro, the E-flight DS75 can't.

Good luck!