Wanted to share this door opener with everyone. It works so well and should have many applications for about anything with small moving doors. This uses a regular size MG996 180 degree servo, controlled by Arduino board or RC transmitter-receiver. This design opens in a wide arc from little movement of servo and has great leverage for the beginning of the lift. Pulls the door shut and holds it. I have the servo working from 13 degrees shut to 150 degrees fully open, so there is a lot more room for bigger doors or longer arms. This is really quite powerful, I have a delay built in to the software to make it look more to scale, but the servo slams the door pretty fast without it. In this application the gear case puts the arm in the middle of the servo, but sure will work just as well with RC airplane type push rods right on servo. My first design with linear pushed at the door instead of up on the door like this does.
Here is a link to a YouTube Video showing it working https://www.youtube.com/watch?v=vqUzjV5_Pv4
This was very interesting working with the length of the servo arm. One side needed less throw than the other. Never would have guessed that one. But it works. I notice they do not close the same but reach the ends at the same time. Very interesting. Was able to fine tune the doors by the length of the bone arm from servo arm. If you need some assorted length Bone arms let me know.
Added PDF with pretty accurate anchor placement measurements.
This stuff goes with the Tank Track 2in, Tank Idler arms, pins and other tank parts in my things.
11-26-2014 Just added some heavy duty gears for the gear case. The old ones didn't print very well and teeth didn't hold up. The new HD gears have fewer teeth but they are bigger and will print solid.
Added a PDF layout sheet that I hope will help you. Going to have to play with it to adapt it to whatever, but that is the hole idea.
The gear case screws into whatever the servo is mounted on. Drill to .120" and use #4x3/4" screws. Case will need raft and support. Gear case cover, no raft, screws to case with gears inside, 4x3/8" screws.
The servo gear will print on table. Drill a little smaller than your servo shaft and push on making groves. A 3mm machine screw hold the gear to MG996 servo. I found it really handy to be able to turn the gear on servo to time the gear with the arms. The MG996 servo output shaft diameter is .220" so a little less.
The output gear needs raft and support. Drill out the case and file down to fit so it turns freely with case cover screwed on. A dremel tool that flat cuts on the end was very handy to go around next to gears. Drill out the hex for arm at .093", 4x3/8" screw.
The supports for the arm will need raft and support. Made some universal supports you can use on doors and one end of arm. The ones for the tank will be different.
Arms will need support on the long ones. All of the arms can be attached using a 4x1/4" screw and flat washer with .180 center diameter. Drill holes for screws to .093". Run a small file around the stubs and drill arms to fit. The stubs on arms and supports are .250" but never print perfect that small. Drill the arm eyes in increments to fit. Start with a "D" or "E"/1/4" (.250") bit. Most of them fit nicely with and "F" (.257") or "G" (.261") bits.
The more time you spend fitting everything together nice and tight but moving freely the better the mechanism will operate (don't look at my sloppy fit).
The servo arm for tank needed the arm connecting to the left side of tank with less throw than right. The longer the main supported arm and short connector to the door arm the wider the door will open. Have fun!