Thread: Assan GA250 DS520 compatability.

As the title says I have a problem with a GA250 running a DS520. It works ok on the bench with a multiplex standard servo at normal slowest analogue speed and also runs it at the top digital rate of 1.5ms 333hz. The servo responds in a fashion and complains. I expect it would get hot and blow up if I left it too long.

When I connect the DS520 it occassionally works, not very often, perhaps 1 in 20 switch ons. I thought I'd broken the cable in the DS520 as I couldn't get it to work until I'd taken it apart. When I checked the signal levels found the frequency was very close to 333Hz but the voltage level was very low at around 1.5V. It wasn't stable either, even though the gyro was in rate mode and should have been outputting 1.5ms every 3ms. I assume my meter is reading the dc average and so the peak value must be 3V. This is a very low value and I'd like to know if anyone can tell me if there is a standard output voltage from gyros and a standard input voltage for servos.

I could have found that the combination worked ok and it could have failed for no reason during a flight. I wonder how many problems can be put down to this? It may be another property of the input signal like risetime that is the problem or capacitative loading/ input impedance on the servo input.

(I am running at 5.6V at the moment.)

I used a GA250 for quite a while with a DS520, worked well.
Here's a thread with some findings: Assan GA 250........Help guys!!! - Heliguy.com

Thanks for the thread. I couldn't see any findings in there, perhaps I missed them. There seemed to be problems or people thought there were problems with gyro initialisation. That isn't a problem with mine. I've now set it to analogue mode and it works every time with a multiplex old style servo. I think I can solve the problem with a single schmidt buffer or any cmos buffer or a simple transistor amp to get the right logic level to drive the servo. I'll look at the voltage level on my Futaba 401 and see what that gives out.

We can make simple test gear to check compatibility. Servo testers might do it. Once the servo starts it seems to be ok and a single pulse will kick it into operation. I could probably make it work with a resistor and a switch or by a momentary short from 5V to the input of the servo. That may damage other things though.

I've cured the problem. I don't know if it is the gyro or the servo or a combination of both. Well it is a combination of both. I used a failsafe alarm that plugs in line with any servo and makes a loud noise when no activity occurs. It also gives a new input and output interface. Mine cost about £2.50 from epatchpark on ebay. I'm using it at analogue 1.5ms and 70Hz as my DS520 is now in bits looking for the fault. Getting into servo programming is a bit tricky for me. Age discrimination I think.

It seems my guesses were right. I sent an email to Assan last night giving the technical details. I got a reply this morning. I'm very impressed. No nonsnse. There is a problem and anyone using old style servos is living on borrowed time. This is the reply:-

Dear Mr.John,

thanks for your letter.

you are right,GA250 send 3v signal out and DS520 need 5V signal in.
one simple way to slove it is use a signal booster,HK's code is 8356.signal booster can increase the signal level from 3V to 5v,for old style servos'.


yours sincerely,

wang