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question about the HS-75BB

Old 07-26-2018, 11:14 AM
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Hello,

I build model airplanes for more than 30 years, but strangely it's the first time I setup a Mechanical retract ( I usualy go pneumatic or electric).
I am assembling a ultrasport 46 ARF ( great planes) for a fellow . And I have a question about the retract servo . That is maybe a dumb question due to my lack of experience with mechanical retract setup
The booklet pictures show the hitec HS75BB instaled in the wing. there is a picture showing it gear up and a other one gear down. If you look those pictures you clearly see that the servo doesn't make a full 180 degrees travel. According to the asembly booklet it seems that the servo is "blocked " by the gear mechanic in down position and unable to complete the full travel.

Are those servo designed for such a condition ? Do they drain a lot of curent when in that situation ?

Thank you for your help and sorry again for my lack of experience with mechanical setup
Old 07-26-2018, 12:11 PM
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So the way to do this is thus:

Measure how far the pushrod moves from lock to lock. Lets say its 1" for simplicity. Then to operate properly you need a servo wheel with the pushrods connected 180 degrees from each other and exactly 1 inch apart across the servo wheel. A blank wheel where you drill holes is often the only way to get it perfect.

Voila, no binding.

Retract servos sweep then shut off so they aren't draining the battery by applying torque to hold the gear up.
Old 07-26-2018, 12:50 PM
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Originally Posted by BarracudaHockey
So the way to do this is thus:

Measure how far the pushrod moves from lock to lock. Lets say its 1" for simplicity. Then to operate properly you need a servo wheel with the pushrods connected 180 degrees from each other and exactly 1 inch apart across the servo wheel. A blank wheel where you drill holes is often the only way to get it perfect.

Voila, no binding.

Retract servos sweep then shut off so they aren't draining the battery by applying torque to hold the gear up.
Thanks a lot,

understood loud and clear

but I am still concerned about this particular airplane setup. It clearly apear from the pictures I can see that the servo will pull on the pushrods and hold the gear down without being at full 180 degrees travel, it will be stopped around 140 degrees rotations ( the pushrods won't bent ( because they are pulled) but the servo will be stucked by the gear down configuration.
will the servo shut off either he didn't made full rotation ?

hope you understand what I try to explain with my poor english

regards

Last edited by SALMONBUG; 07-26-2018 at 01:27 PM.
Old 07-26-2018, 01:30 PM
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If thats what you are seeing then its not setup with the correct geometry.
Old 07-26-2018, 01:52 PM
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Originally Posted by BarracudaHockey
If thats what you are seeing then its not setup with the correct geometry.
It's like that. They give a disance beween the center of the servo arm and the EZ connectors that hold the pushrods in place, but this distance is to accomodate the location of the pushrods housing glued in the wing and not l the travel the pushrods need to do.

I don't have a lot of clearance ( it's a ARF ) to solve that, so I ask myself " how will the servo handle that ? Will it try to move and pull on the pushrod non stop, or will it remain steady at a given moment " ?

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