Servo and Actuator Choices

[DanH]

I want to install a servo or linear actuator inside the engine cowling, thus temperature rating becomes important. In-cowl air temperatures can reach 230F. Average temperatures (if such a thing can be said to exist) are 180-200F.

The familiar Ray Allen actuators have a "sorta" temperature rating....the FAQ page suggests 180F as a max. The limiting factor appears to be the nylon gears. They are not cheap, but at $279 you have a complete system with position indication.

There are RC servos with enough torque to do the job, and Eric at Perihelion sells a nice little rotary position controller for them:

http://www.periheliondesign.com/more...Controller.pdf

Using that controller you don't really need a position indicator, as knob position tells you servo position. However, the datasheets for standard RC servos seem to suggest 140F (60C) as a max. That rating seems to apply to the metal gear choices too, so I assume internal electronics dictate the limit. I know very little detail about RC servos. Any thoughts?

There are nice linear actuators which can be controlled with the same Perihelion controller (or any other pulse-width controller). Here's an example, but again the temperature rating looks a little weak for the task:

http://www.firgelli.com/pdf/L12_datasheet.pdf

Can anyone suggest a small servo or actuator which might be suited for the engine compartment? Need an inch or less of travel at about 10 lbs max.

[rocketbob]

Why not use the ray allen servo but place it somewhere cool and use a simple push/pull cable to it. I have about 50 feet of teflon-lined cable, same stuff spruce uses to make throttle controls with. Let me know if you want a piece and I'll send it to you.

[868RM]

Dan, I am using a firgelli to operate the oil cooler shutter . Fastened just above the plenum connected directly to the arm of the shutter. Only 30 hrs. but flew in some 95 degree oat and some high break in temps. It worked fine this morning @ 37 degrees. Ron

[DanH]

Originally Posted by rocketbob

Why not use the ray allen servo but place it somewhere cool and use a simple push/pull cable to it.

Thanks Bob. May come to that, but the design is a variable cowl exit constructed as a unit....door and actuator on a single cowl belly panel. The beauty of an actuator is simply unplugging an electrical connector to drop the lower cowl.

Originally Posted by 868RM

Dan, I am using a firgelli to operate the oil cooler shutter .

Upper cowl, certainly a warm spot. Which model are you using Ron, the little L12? What are you using for a control?

[WingsOnWheels]

The L12 or new L6 actuators seem to be the best bet. If you want variable control you could go the servo route or use their indicator with a momentary toggle. If you are just diong open/close then the limit-switch version with a open/close toggle would be very easy.

[868RM]

Dan, PQ12 controled with self centering toggle switch.100:1 ratio with potentiometer to send position to garmin G3 but have not wired position wires yet. Winter project. Ron

[DanH]

Originally Posted by 868RM

Dan, PQ12 controled with self centering toggle switch.100:1 ratio with potentiometer to send position to garmin G3 but have not wired position wires yet. Winter project. Ron

Appreciate the feedback Ron.

Need short travel and high force for this cowl door, so I'm going to try an L12-S 10mm 210:1.

Traded a note with Firgelli asking about the low max temperature rating. The response indicated it was based on concern for plastic motor parts and the PCB, if present. Thus the choice of an "S" (limit switch) model....don't think it has a PCB. I find it hard to imagine a problem with motor plastics....we'll see.

With no servo PCB, control is just a simple DPDT (like a flap switch), no position indicator.

FWIW, there does not appear be be any readily available actuator rated for 200F and more.

[Lars]

This is sort of off the wall, but given the relatively low force and travel requirement, why not cable actuation?

[RV7Guy]

Originally Posted by 868RM

Dan, PQ12 controled with self centering toggle switch.100:1 ratio with potentiometer to send position to garmin G3 but have not wired position wires yet. Winter project. Ron

Hey Ron,

I was looking at the Firgelli for the same purpose. What are you using to lock the oil door in position.

I have an idea in mind and was wondering what you might be doing.

Thanks,

[868RM]

Darwin, I am using the "shutter " type mounted between baffle and oil cooler.It can be tweaked a bit to hold in any position (slight drag). I thought about a hinged door on back side with a scissor type linkage that went over center at full open but that only offered full open and closed or almost closed with good rigidity. I put a stop on the shutters so they are about 20% open in closed position. Seems to be working good so far. The ribbon wire needs to be supported very well. I tried to use one of these servos on my cabin ht. control but broke the ribbon wire even wrapped in shrink tube ( on engine side ).Went to a cable on cabin side until I get support sorted out.If you email me I will send you some pics. Thanks Ron