9gram Micro Servo Mounting for Lego
I purchased one of MindSensors 8 Channel Servo Controller for NXT (NXTServo-v2)
a few weeks ago and needed some servos. I found 6 x 9gram Micro Servos for around $20 on eBay and two 30grams with metal gears for a similar price including P&P. I am quite amazed with the amount of torque out of something half the size of a matchbox.
The next thing was to come up with a method of interfacing them to my lego masterpieces. I toyed with a couple of possibilities, such as manufacturing a mounting kit like MindSensor supplies with the Servos they sell. Unfortunately my efforts along these lines weren't all that successful and were aesthetic failures.
So I decided maybe I would end up donating some more cash to MindSensors and headed of to bed. Some hours later I woke at 3:30am with the answer. It was extremely simple mount and drive interface requiring a 24 Tooth Gear, a Technic, Thin Liftarm Triangle, some Plumbers PVC Pipe Glue and the rest of the 3 remaining parts were in the bag the servo came in. A Dremell or other Small Multitool for cutting and grinding small model parts is needed for subtle modification of the gear and triangle.
To mount the Technic Liftarm Triangle onto the Servo, first you need to modify the it as shown below. The 24 Tooth gear needs to have both sides modified as shown below.
The modified Technics Triangle should slide tightly onto the lug on top of the Servo near the Shaft. It's a good idea to get another straight liftarm and place the Servo Shaft in one of the arms holes and check that the holes in the Triangle line up with the shaft incase you need to shave off some of the Triangles Base. With the Servos I used they lined-up perfectly without touching the base of the Triangle. Remove it and place a good amount of the PVC Glue to the Triangle and the contact points on the servo and put the two parts together checking alignment and leave for 30-45 minutes.
Next center the rotation of the Servo Shaft and fix the 'White Cross' part provided to it and screw in place. Next place the the 24 Tooth Gear on top of the White Cross and use two of the provided mushroom top Servo mounting Screws. That's it!
The Advantage of using the 24 Tooth Gear as the drive attachment is that it allows the following connections unlike other parts:-
Standard Lego Axel
Standard Lego Joining Pins
Standard Lego Gears or Rack
I also used two Lego Technic Triangles for mounts in a similar manor on a couple of 30gram Servos as well.
When it comes to gluing Lego parts together or to other plastics, I have found the Plumbers PVC Adhesive the best. Unfortunately it comes in white and Electric Blue shades only. I have broken parts which were repaired many years ago with it and are still preforming well. It welds the joint by melting the two surfaces together similar to plastic model glue, but nowhere as strong and reliable. Just remember to use the "Plumbers Friend" OUTSIDE, unless you wished to become slightly stoned, followed by headache and vomiting if you get too enthusiastic!
Checkout my Wii Nunchuck Servo Controlled Zamor Cannon in the following post which was my first project using the servos and controller. It uses two 9gram and one 30gram servos to control firing, Altitude and rotation. Not a single Lego motor in sight!