I just received the May issue of Kitplanes. Article on page 18 about a simple auto pilot. Looks like someone decided to design a simple autopilot using RC giant scale servos powering large trim tabs on the control surfaces like I did. I built an autopilot in 2008 using giant scale RC servos and installed it in my little VW powered single seat homebuilt Super Cub, (SSSC). Had wing level and pitch with electric trims on each and leds to indicate what the AP was doing. Along with standard rate turn right and left. Was planing on coupling it to a GPS but never got around to it. I flew the AP , or rather it flew me, for 2 years. Worked good, and you could also fly the airplane with the trim knobs. I sized the AP tabs to control the airplane yet if there was a failure it would be easy to overcome and fly the airplanes with the controls. After 2 years I got tired of the AP having all the fun and took it out but still use a electric trim but not using a RC servo. Nothing wrong with the AP and it always worked good.
The rate gyro was from Newark-in-one that is no longer being manufactured. Square pulse for the RC servos made using a LM-556. For pitch, ( locking on a pressure altitude) using a matched set of 2K thermisters in a cavity in parallel, on the lid of a 1 qt glass jar. If the plane climbs the less air pressure forces air out of the container and cools the first thermister more that the second one and unbalances a circuit. The unbalance would vary the square pulse generated by the 556. All using op-amps. The thermisters driven enough for a temp of about 150 degrees. It would lock on a pressure altitude with-in 25', any tighter that that , the pitch would start oscillating. The RC servos that I was using has a torque of 375 inch oz. No lack on power flying the tabs.
You can get RC type servos now at about any torque you want here. Firgelli Technologies - Micro Linear Actuators
I am using a servo from this company for my electric elevator trim.
The yellow and black tab was what I used on the right aileron. The size was correct for my slower 80 mph airplane.
I'm using the same red elevator tab today for elevator trim that I used on the AP.
Like the Kitplanes article, I mounted the servos on under side of the inspection plates.
Dan
The rate gyro was from Newark-in-one that is no longer being manufactured. Square pulse for the RC servos made using a LM-556. For pitch, ( locking on a pressure altitude) using a matched set of 2K thermisters in a cavity in parallel, on the lid of a 1 qt glass jar. If the plane climbs the less air pressure forces air out of the container and cools the first thermister more that the second one and unbalances a circuit. The unbalance would vary the square pulse generated by the 556. All using op-amps. The thermisters driven enough for a temp of about 150 degrees. It would lock on a pressure altitude with-in 25', any tighter that that , the pitch would start oscillating. The RC servos that I was using has a torque of 375 inch oz. No lack on power flying the tabs.
You can get RC type servos now at about any torque you want here. Firgelli Technologies - Micro Linear Actuators
I am using a servo from this company for my electric elevator trim.
The yellow and black tab was what I used on the right aileron. The size was correct for my slower 80 mph airplane.
I'm using the same red elevator tab today for elevator trim that I used on the AP.
Like the Kitplanes article, I mounted the servos on under side of the inspection plates.
Dan
