capt17

I am building a GP .40 sized corsair and installing push/pull type retracts. I'm trying to get everything set up so that I can use a servo for each strut. Right now I am toying with a Hitec 75BB, 180 degree retract servo. My problem is that I don't need all 180 degrees. It is perfect gear up (holds with no play), but gear down it rotates to approx. 120 degrees then stops due to the stops on the gear mechanism. It holds the gear down great with no buzzing but this can't be good over time can it? Or are 180 degree servos built to not go all the way when resistance is felt? If teh above is bad, can I use a proportional servo for retracts where I can set the endpoints? Hitec says that the 77BB is the same as the 75BB I've been messing around with but proportional. I can't find any torque specs on the 77BB to confirm. So am I ok to use the retract servo at 120 degrees rotation and/or is a proportional servo safe to use in a retract application? Thanks!

MinnFlyer

My Feedback: (4)

Move the pushrod to a closer hole in the servo arm

w8ye

My Feedback: (16)

You need to change the effective ratio of the servo by moving the rod closer to the pivot center of of the servo arm so it is 180 each way

exeter_acres

My Feedback: (2)

asking here......

can you adjust end points in the radio for retracts?

w8ye

My Feedback: (16)

Some transmitters you can

But I would recommend hooking the actuation linkage up correctly in the beginning

RCKen

My Feedback: (9)

Exeter,
Normally no. Retract servos are different from full proporational servos. The retract servos usually only travel 180°. And if you try to use a normal servo instead of a retract servo it will need to constantly draw power in order to hold it's position, which will drain the battery in a hurry. A retract servo goes to the end of it's travel and then stops, which doesn't draw any power to keep it's position.

Ken

capt17

OK thanks guys. I'll keep tinkering with the linkage!

MinnFlyer

My Feedback: (4)

Just measure the amount of travel the retract needs (In this case, let's say it's One Inch)

Now take one of those big round servo wheels that you always throw away and measure 1/2 of the travel from the center to both sides.

Drill holes at those locations and insert EZ Connectors into the holes.

exeter_acres

My Feedback: (2)

Thanks... I knew about the standard servo and the retract not being proportional... was just curious if you could set the radio endpoints for it..
appears not..

Thanks!

momon

Thanks Mike . great tip .

j.duncker

My Feedback: (2)

I like simple installations with a single battery but with mechanical retracts the possibility of having a stalled retract servo is quite high and this will flatten the battery quickly so using a seperate battery for the retract servo is a good idea.

Here is one way of doing this.

You need an additional switch and a 'Y' lead, the latter modified to allow the second battery to provide power exclusively to the retract servo. To this end the red (positive) lead is either cut through or removed from the receiver end of the plug, thus ensuring that only the secondary battery pack provides power to the servo, eliminating any possibility of a stalled retract servo flattening the Rx pack. The 'Y' lead is then connected to the retract channel of the Rx, with the second battery being plugged into one of the sockets of the 'Y' lead via a switch. The retract servo is plugged into the leads remaining socket.