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T-REX 450 › GP 750 Gyro limit setting issue/question
03-31-2009 06:23 AM  9 years agoPost 1
zsultan

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USA

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Hi,

I am trying to set limits for the tail servo (DS520) on my 450 Pro, I know that throw on one side is slightly higher than other because the DS520 doesnt center exactly. before setting limits i plugged in DS520 in rudder channel and centered the servo horn and also mechanically centered the slider.

I followed the instructions in the manual for setting tail servo limits.

1. I pressed setup button for 2 sec and the main/top LED starts flashing.
2. Choose Limit by repeatedly pressing the setup button
3. once limit LED is lit, moved rudder stick to left (LED on top turns green) until the end and then moved the stick to right (LED on top turns Red) until it reached the end. do i need to do anything after that?

My GP750 sets limits on only one side thats when i move the stick left and doesnt set when the stick is moved to right (towards tail case).

What am i doing wrong. Please help i am trying from yesterday.

I did everything from mechanically setting up zero pitch on tail blades to centring serrvo again today, no luck. Really frustating.

Please advise.

Thanks in advance.

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03-31-2009 10:25 AM  9 years agoPost 2
caseyjholmes

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Portland, Oregon

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I know that throw on one side is slightly higher than other because the DS520 doesnt center exactly.
The servo will not center perfectly. The linkages must be set up to account for a centered pitch slider when the servo is as centered as the gyro sees it.

I think if you are hitting one side of the limit and not the other, that your linkage is not centered to the offset of the servo?

I had the limits set shorter on my align gyro but I can't figure out how to get it to do it again. My limit are about maxed out both side and going through the limit setup routine does not seem to change the limits anymore while it did at least one time. I gotta figure out how to get the limits set back up a hair less on each side. It's not binding the slider but I'd like a bit more clearance on the slider between each end of the tail shaft.

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03-31-2009 03:37 PM  9 years agoPost 3
zsultan

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USA

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Thats what i want to do, i want to reduce the limit on the gyro so it doesnt bind on both sides. I was able to do it on one side but not on other. Its very easy on 401. not sure why it doesnt do it on the other side.
The linkages must be set up to account for a centered pitch slider when the servo is as centered as the gyro sees it.
I have setup my pitch slider to have zero pitch, since the servo is not perfectly centered there will be little more throw on one side, i am trying to setup equal throw by reducing the limit on one side little bit more than other so that they dont bind.

Does the GP750 sets limits independently on each side or its like 401? I also tried making the limit on the side which its limiting properly very less to see if the other side works no luck.

Please advise. Its real PITA :-)

Thanks

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03-31-2009 03:48 PM  9 years agoPost 4
bulldogs

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~OC~ ,CA USA

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Does the GP750 sets limits independently on each side
Yes

~TEAM OCHC~
A strong man stands up for himself a STRONGER man will stand up for others.

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03-31-2009 03:51 PM  9 years agoPost 5
zsultan

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USA

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can someone walk me through the process of setting limit on gp720? i followed the manual may be like 50 times no luck it sets only on one side.

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03-31-2009 04:26 PM  9 years agoPost 6
caseyjholmes

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Portland, Oregon

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Like I said,
the limit function on my gyro does not seem to be working as stated in the manual either. Somehow I was able to do it once though. WhenI went to try and reset the limits after some mechanical adjustments again, I could not do so. I will have to go over mine more today and see what is going on with that. If you are able to control one side of the limits, you are one up on me at the moment because I can (no longer) set either.

I got lucky though and it seems my limits are set perfectly now even though I can't change them I don't know what's going on with that, have to look in to it more. The limits don't seem to change after following the manual limit setup procedure on my gyro at the moment.

I think when I set them up the first time and it worked, I was using a 4.8v nicad setup battery. Now I'm running off the BEC of the ESC (6V) and it doesn't want to change. I have no idea if that means anything or not though.

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03-31-2009 08:08 PM  9 years agoPost 7
caseyjholmes

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Portland, Oregon

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I looked at my gyro limit settings some more. It's working fine.
It looks like I could not limit the tail servo throw any more because I was at my minimum limit already. I tried programming increased limits and it worked. Then I programmed back down to minimum limits and it happens to be the perfect amount of travel.

I have about 1-2 degrees of tail blade pitch when the gyro centers my tail servo. Limit is at minimum. Ball set as manual recommends.

If your limit is binding on one side, your linkage is not center.
With the provided ball distance, the minimum limit is the maximum you need the slider to travel.

It does not matter if the tail servo centers perfectly. Turn the heli on and the gyro centers the servo. then turn it off. Now adjust your linkage so it's in the center of it's range of travel. If it's adjusted right, it should not bind on either side. Your limits are probably already at minimum and it's just a linkage adjustment.

If all else fails, move the ball in on the horn, and then you can increase the limit and maybe even line the linkage up better.

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03-31-2009 09:22 PM  9 years agoPost 8
zsultan

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USA

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Thanks caseyjholmes

I will try it tonight. So having pitch on tail blades when the servo is centered is not an issue? If the slider is centered, blades should have zero pitch right? How do you know if the limit is at minimum or maximum?

Little confused.

Let me tell you what i am going to do.

1. I have my tail blades at zero pitch when gyro centres the servo. since the tail servo horn is not perfectly at 90 it will have more throw on one side than the other.

2. I will adjust the tail control rod length so that i can move the slider little bit towards the end thats not binding, now i will have some pitch on the tail blades.

3. After that i will try to limit the throw with gyro limit function.

Please let me know if its OK.

Thanks

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03-31-2009 11:54 PM  9 years agoPost 9
caseyjholmes

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Portland, Oregon

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2. I will adjust the tail control rod length so that i can move the slider little bit towards the end thats not binding, now i will have some pitch on the tail blades.

3. After that i will try to limit the throw with gyro limit function.

Please let me know if its OK.
Sounds about like what I did.

I think I actually have some anti-hold pitch built in to the tail blades when my slider is centered. Seems odd, but it's working for me!

I bet if we move the ball in as least amount as possible on the horn you could tune limits in a little better and the linkage would line up nicer. It comes at a slight loss of speed I think though.

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04-01-2009 12:57 AM  9 years agoPost 10
zsultan

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USA

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One more quick question did you use main shaft spacers to reduce play? page 14 of the manual

Thanks

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04-01-2009 01:25 AM  9 years agoPost 11
caseyjholmes

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Portland, Oregon

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Yes.
At first I assembled it without noticing those. When I found the play, I went looking through the manual to see if there was a spacer. The manual said they were in the spares bag. Low and behold there were two main shaft spacers in there. I used both the first time, they both fit and removed the vertical main shaft play completely.
I kinda like the no shaft collar design. Only thing is it will be tough when you strip the nut in the plastic gear hex shaped nut retainer of the tail gear to remove the main shaft. You know, when the nut is spinning in the gear and the gear wont hold the nut to pull the screw out

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04-01-2009 04:38 AM  9 years agoPost 12
zsultan

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USA

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caseyjholmes,

I adjusted the tail control rod one full turn and it works now, No binding on both sides.

Thank you very much for your help.

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04-01-2009 04:41 AM  9 years agoPost 13
caseyjholmes

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Portland, Oregon

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Cool
I adjusted the tail control rod one full turn and it works now, No binding on both sides.
That is basically what I had to do. It was off center on one side. A turn of the link and the limits were even.

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10-09-2009 08:07 PM  8 years agoPost 14
bowies12

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Surrey - UK

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Great post, I just figured out my problem. Thanks for all the suggestions

Limits were already at minimum. Cant go less than that!!!! I had to use a slightly shorter servo arm.

Fat birds can't fly

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10-10-2009 01:59 AM  8 years agoPost 15
helibro

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hamilton, ohio

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when the gp750 is all set up and after hovering in rate mode and adjusting the linkage to hold should the tail slider still go all the way from the tail case to the tail grips? i get it to hold a hover in rate mode so i know the linkage is right but the slider touches the case but not the hub?

hey! were is the reset button!

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10-10-2009 04:48 PM  8 years agoPost 16
dfrazier

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Sulphur, La

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I just got a 250 with a 750 gyro. The way I set endpoints is to first flip the switch on the transmitter to get it out of heading hold mode and put it in rate mode and then hold the button on the gyro until it enters setup mode. click the button until the limit light is lit. Very slowly move the stick to the left until it gets near the end but not hitting and hold the stick there for a second then slowly move the stick to the right until it gets near the end but not hitting and hold the stick there for a second then move the stick back to the center. Push the button on the gyro again to the next step or leave it alone and it will end setup mode on its own after about 10 seconds. After that you can check to see if it is set right by leaving it in rate mode and move the stick right and left and verifying it does not bind.

Sorry for the long winded post but I have to explain it as if I was the one needing help. I can be a little slow sometimes.LOL

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10-10-2009 06:15 PM  8 years agoPost 17
str8den

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NE U.K

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i couldn't get the end-point to set on right-stick (tps towards t/case) on my 500. Sent it to the main man to have it tested; nothing wrong with the gyro - turns-out that the gyro has to 'see/recognise' at least 50% of the tailservo movement; which i assume to be around 25-30 deg. of rotation??

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01-17-2010 04:37 AM  8 years agoPost 18
meowsqueak

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New Zealand

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Just a related problem - I understand how to set the limits on each side, but what if the rudder servo does not move *enough* to get close to the limits at all? I've got 4mm of spare space on each side of the current limits that I can't get to, so I can't set the endpoints to be "out there" either.

One option would be to use a servo ball further out, but surely there's some way to tell the gyro to use wider endpoints?

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01-18-2010 04:20 PM  8 years agoPost 19
str8den

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NE U.K

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meow, just for a guess, you could bump-up your rudder epa/atv to something like 125% or more, then use the limit adjuster on the gyro.

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01-18-2010 05:56 PM  8 years agoPost 20
bowies12

rrApprentice

Surrey - UK

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Str8den,

That will not work.
Heading Hold gyros operate differently from the old fashioned rate only gyros.

The Rudder epa/atv controls the piro speed and has nothing to do with travel adjustment.

The fix here is a bigger servo horn. Its important to get the heli mechanically correct before large amounts of fiddling in the radio or gyro itself.

Fat birds can't fly

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