Electric retracts - RCCanada - Canada Radio Controlled Hobby Forum
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Old 06-20-2012, 07:14 AM   #1
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Electric retracts

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Can a computer radio limit the travel of a 90-degree electronic retract to 85 degrees? Thank you.
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Old 06-20-2012, 08:01 AM   #2
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Re: Electric retracts

No you cannot. The retract control circuitry and mechanism geometry control the total sweep angle.

Here is some info I posted on another forum regarding how these work:

Instead of physically connecting linkages from external servo(s) to the retract mechanism servoless retracts include everything integrally, (we'll ignore air operated for now).

Along with a much simpler and more compact setup there are other advantages. The first is that with each unit built up ahead of time there would be no adjustments required for up and down to ensure the gear locked either way. The internal board has all the switches, motor drive electronics and also most likely current sensing circuitry to shut down the drive if there is a bind or interference with retract action. This is particularly important if there is only one battery source as a stalled electric motor can draw a lot of current and interfere with the rest of the radio and flight system.

That internal board also interprets the signal from the Rx same as a standard retract servo. That means it will only travel the full amount each way depending on where related to center position the signal is for that channel.

Remember that all the receiver channels have signal outputs just like there was a servo connected. If you had a servo plugged into the gear channel you would only see it sweep one side of center to the other when the switch is flipped with the amount of sweep adjusted in the "Travel" or "AI" parameters page. There is no stick motion to follow.

A gear servo or integral servoless retract reads the output of the channel and if even slightly off center it will run the system all the way to the end in that direction. If you have a sequencer it should work fine, just remember the following.

The other advantages of servoless retracts over other types, particularly air is that the sequence is mechanical and should always require the same time to accomplish. This makes sequencing much easier and more reliable. If I have any complaint about servoless retracts it is that sometimes the gear transit is not scale and it is not adjustable.

Due to the above advantages I am swapping all my installations over to servoless.
One thing I did not cover is the mechanical portion that physically denotes the total sweep angle as I am really only taking an educated guess there. Basically the slider slot can be moved closer or further away from the gear pivot and/or the start and stop point for the motor readjusted to set how far that gear pivot moves. This is physical and your radio system has no control over how it was machined and assembled.

In a perfect world you want that slider to be resting at 90 degrees to the gear pivot drive pin so that the forces on the slider are perpendicular. In simple terms the loads are NOT along the slider travel axis and therefore cannot force the slider to move and the gear to then rotate. With servoless retracts which use a worm gear drive this also avoids loads on the worm gear and end supports.

Hope that helps.
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