DIgital Torque Meter for Rubber Powered Planes

thingiverse

This digital torque meter is designed to carefully wind rubber with precision for indoor rubber powered model airplanes. I created this around a scale that can have auto-off disabled at will. The selected scale features a low-profile display that allows tilting to a higher angle, providing better distance visibility. This meter approach draws heavily from Jake's innovative design. Print Details: You'll need to print one of each, except choose only one arm length to print. The arm lengths allow different units as follows: 2.8" arm: set scale to grams, readout is in oz-in * 10. This is my preferred setting, where 0.5 oz in will display as 5.0. 50mm arm: set scale to carats, readout is in g-cm 1-inch arm: set scale to ounces, readout is in inch-oz You'll need to print two collars. Assembly: The assembly process is very similar to Jake's design, and details can be seen at the HPA forum. The meter is more similar to the later version, so make sure to read through to the end. You'll need the following items in addition: * Scale: Amir 500g scale, available on Amazon. MUST BE AMIR, not a look-alike, to disable auto-off and ensure parts fit * Dubro 1/8" wheel collars (3) * Dubro 4.0 x 14mm socket head cap screws (2) * 4-40 x 1/4" set screws, such as those found on Amazon (3) * 1/8" ball bearing assemblies, available on Amazon (2) (I preferred these over roller bearings) * 1/8" music wire or shaft, about 3" long * 1/32" music wire for hook, about 3" * 1/32" music wire for anchor, about 1/2" long * Kevlar fishing line, I used 60# test The scale must be carefully disassembled before use. Carefully pry the SS tray off the platform using a small screwdriver, taking care not to distort or load the load cell. Once that is done, you can access all the screws to disassemble. Keep the small screws. When removing the electronics, keep track of which buttons go where. Use a Dremel to cut out the battery holder, or purchase a 2xAAA battery holder online. Mount the electronics in the front face panel, reusing screws from the scale. Pass the load cell and battery box through the largest opening on the front, then place the display face on, top first, and snap it down into place. Use two of the longer tiny screws from the scale to screw the faceplate on from under the torque meter. Glue the battery box in with Shoe Goo or Goop. Mount the load cell on the appropriate stand depending on the length of the load arm, using two 4mm bolts and a spacer from the original scale. Be sure to mount it on the correct end, just like in the original scale. The wheel collars are a tight fit into the collars and arms, at least with my printer. Insert a Dubro set screw into the collar, screwing it down well below the surface. Then align the hole in the plastic with the set screw hole in the collar, and press the collar in with pliers. You may need to tap it in with a drift. Unscrew the set screw, and it will cut threads in the plastic as it comes out. Now insert a 1/4" long set screw through the plastic. If you don't do it in this order, you'll have great trouble getting the set screw aligned into the collar. Follow the Hip Pocket tutorial for assembly of the shaft. The front (outside the case) needs to be long enough for the plastic collar to clear the display faceplate. Grind a small flat on each set screw to ensure it doesn't slip. Make sure motion is free, and if not, try re-seating the bearings.