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HomeAircraftHelicopterAntiques or Out of Business › GMP Legend Electronics Upgrade
03-14-2015 04:55 PM  3 years agoPost 1
tonybcrazy

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Raymond, ME USA

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Not sure if this would fit better in an electronics sub forum but here goes anyways;

I inherited a GMP Legend FBL about 20 years ago from my grandfather who had never really managed to fly it. I was a kid with limited means so I never managed to fly it neither. Last spring I decided I finally wanted to see it in the air. I set about getting it airworthy again. It needed new tail and main rotor blades which I managed to replace with modern Align and KBDD equivalents. I decided to give the original Airtonics Quantum PCM 8 ch. radio system with mechanical gyro a shot. I replaced the batteries and everything seemed to work well. Despite this being my first and only heli I managed to learn hovering fairly well. However the age of the radio started to become a problem. On one occasion all of the servo center positions seemed to shift slightly. Also on two occasions the tail servo just decided to go to full throw in one direction and stay there regardless of the port it was plugged into. After the first time that happened I replaced the servo with a spare and the second servo did it again a few sessions later. Luckily none of these glitches resulted in a crash but I am reluctant to try to continue flying without bringing the electronics into this century. I am looking for advice on the radio system but particularly the servos This is what I am currently thinking of purchasing:

Spektrum Dx 8
Spektrum AR7200bx FBL system with a satellite

What I am unsure about are the servos. The heli currently has all Airtronics 94735 servos which seemed to be very good servos in the late 80's. I think I will at least need a new tail servo but am considering replacing them all. I am on a bit of a budget, I would like to keep the price of the upgrade under $500. I would also like to stick with Airtronics servos so I don't need to setup all new servo horns. This isn't going to be a 3-D setup by any means so I don't think I need ultra high performance servos. A couple servos I have found which seem somewhat comparable to the original 94735's are 94774 and 94846. I really don't have much to go by though so I am interested in others opinions.

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03-14-2015 06:25 PM  3 years agoPost 2
Salesmanheliboy

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Nashville, TN

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I had one of those as well.

If I were you, I'd replace all of the electronics, especially servos. I still have some radio's from 20 years ago that I use for airplane training but servos are all much newer.

I'd guess that there is a good chance that your TR servo going full range may be the gyro and not the servo (since the same thing happened with two servos).

Get some good mid range servos and a new gyro and radio and enjoy. There are a number of excellent choices available and you can move the systems to other models if you want to.

Good luck.

Tim

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03-14-2015 08:43 PM  3 years agoPost 3
madgadget

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St Louis MO

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Check the t/r belt and mid range servos will go a long way to piloting that machine. Let me know if you need anything else. I fly mine at least once a year and still enjoy it.

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03-14-2015 10:55 PM  3 years agoPost 4
tonybcrazy

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Raymond, ME USA

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GMP Legend Hovering:

Watch at YouTube

Here is a short clip of me hovering on the old electronics.

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03-15-2015 10:13 PM  3 years agoPost 5
tonybcrazy

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Raymond, ME USA

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Thanks for the replies. Can anyone suggest good mid range servos? Are the ones I have picked out mid range or maybe a little more than I need?

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03-16-2015 05:35 PM  3 years agoPost 6
madgadget

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St Louis MO

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if it's not broke, fly it until it is!
New generation servos hold center and inputs better. If you have minimized loss motion in the linkages and can maintain control as it appears in your short clip then I would fly it as is. In the event of a mishap and a servo is stripped or damaged then would be time to shop for some align 610 or equivalent. Just my .02..

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03-16-2015 07:31 PM  3 years agoPost 7
TMoore

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Cookeville, TN

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735's are great servos but save them for a plank, analogs aren't the right servo for FBL. ATX makes a ton of reasonably priced digital servos as well as radios that are better suited for modern FBL operation. JR and Airtronics use the same spline if you want to use the same arms but I wouldn't let that determine the servo I bought. You will have to upgrade your flight battery too.

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03-17-2015 12:25 AM  3 years agoPost 8
tonybcrazy

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Raymond, ME USA

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I am reluctant to fly as is. I do realize I am taking a big risk as a beginner flying a vintage heli with limited parts availability. I lucked out on both of the tail servo failures because they happened right at power up. Had they happened in the air I doubt I would have been able to recover. So I guess I want to give myself a fighting chance with a modern gyro / FBL controller. What would be a minimum requirement for the receiver battery? I currently use a 2000mah 4.8v NiMH battery.

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03-17-2015 01:22 AM  3 years agoPost 9
TMoore

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Cookeville, TN

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A 2S lipo with or without a regulator depending on the ultimate voltage of your servos.

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03-17-2015 02:08 AM  3 years agoPost 10
gologo

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Sedalia, Mo USA

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That clip was way too short, could have watched much more....... Looks like you have some nice control of it. Motor also sounds good, is that what
was in it when you got it?

I agree on going digitals for flybarless, whether FBL unit or no-bar. Don't
know about some of the other units, but a simple V-bar mini, which is also
simple to set up, would do every bit of what you want out of the heli, which would also need a good modern digital tail servo to go along with.

Don't know how you would feel about used, but have seen some great deals on
here of quality servos by good reputable guys that I wouldn't hesitate to
buy from. Same w. FBL units........

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03-18-2015 01:05 AM  3 years agoPost 11
tonybcrazy

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Raymond, ME USA

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The engine is the orginally equipped Enya 60xf-4.

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