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Old Aug 30, 2014, 11:05 AM
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Joined Jan 2012
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Throttle and choke servos

I have had 2 x 110oz HV MG servos fail after about 100 flights on an Extra 91". They are used on the throttle and choke, so about 5 to 6 inches behind the firewall and are linked to the engine with a 2-56 metal rod and nylon clevices. They were not "singing' in the min or max positions and the power is A123's.

Both servos do not respond to Tx commands unless I start rotating their arms and even in their new positions they do not stay there firmly.

I replaced both of them temporarily with other identical servos I have and all is well again.

Is this a common problem with some servos ?

Have I got the wrong servos ?

What are good and reliable servos for this application ?

Thanks
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Old Aug 30, 2014, 12:47 PM
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Wintr's Avatar
USA, MO, Florissant
Joined Nov 2010
1,685 Posts
Quote:
Both servos do not respond to Tx commands unless I start rotating their arms and even in their new positions they do not stay there firmly.
This makes me think that they are contaminated with fuel, or just the oil spray. Do you have a seal of some sort that blocks the 'slime' from running back on the control rods? When we set up a P-51, we cut a strip of rubber, the kind inner tubes are made of, and glued it to the fire wall, with a slit that the control rod passes through. The rubber wipes most of the oil spray from the rod, before it can reach the throttle servo.
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Old Yesterday, 06:14 PM
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Joined Jan 2012
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I just opened up one of the servos, which is no longer under warranty, and found that one winding is open. Motor burnt !

The second one has exactly the same symptoms, so it must have a burnt motor as well.

Still no advise as to what is a good servo for throttle or choke ?
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Old Yesterday, 08:54 PM
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Illinois
Joined Sep 2001
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Throttle and choke servos should have wide gearfaces. The vibration is what kills them, not the torque applied. The motors are constantly trying to hold a position - it's no wonder they died.

Use a cheaper servo, one with a wider deadband. It won't try to hold position so hard.

Andy
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Old Yesterday, 09:46 PM
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Joined Jan 2012
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Originally Posted by AndyKunz View Post
Throttle and choke servos should have wide gearfaces. The vibration is what kills them, not the torque applied. The motors are constantly trying to hold a position - it's no wonder they died.

Use a cheaper servo, one with a wider deadband. It won't try to hold position so hard.

Andy
Could you suggest any ?

I just want to look at their specs and understand what you mean.

Thanks
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