This gearbox was designed to work with the Denso Throttle Motor that is given out with the Frist Robotics KOP for several years. The gearbox housing and gears are entirely 3D printed using PLA plastic. PLA seems plenty strong for the limited power this motor has. After running and loading the output shaft of the gear box for several minutes I saw no degradation in the printed gears. There are two sets of gears providing a gear reduction of about 10:1 and 18:1. The total weight of the motor and gearbox is less than 1lb.
The gearbox and gear files are available to all FRC teams complements of "Andromeda One - TEAM #4905". Our only request is that if you print or use the gearbox that you post a picture on our facebook page: https://www.facebook.com/frc4905
Also, if you have any suggestions for improving the design please post them here on Thingiverse. I still have some more torture testing to do, but honestly I think it is way over designed. As time allows I will look into improving and minimizing the design. Any positive feedback you can provide is appreciated. Good Luck!
Gearbox Housing: The gearbox housing was printed with 3 solid top and bottom layers with 2 solid inside and outside layers and 30% infill. PLA filament was used.
Gears: The gears were printed with 4 solid top and bottom layers with 4 solid inside and outside layers and 50% infill. PLA filament was used.
1/4" ID, 5/16" OD, 3/4" long brass bushing
1/4" OD, 1 1/4" long steel axel (cut mine from non threaded shaft of 1/4" bolt)
Three - #8-32 x 2" Flat Phillips Countersunk Machine bolt and nut.
Three - #8-32 x 2" (or longer) Round Head Machine bolt and nut.
One - #8-32 x 3/4" Round Head Machine bolt and nut.
Seven - #8 lock washers
Four - #8 washers
Two - #14S Brass Flat Washers
Two - 0.187" Female Terminal (note these are smaller than common female terminals)
16 - 18 AWG wire
Two - Hex Flanged Bearings - 13.75mm x 1.125" x 0.313"
1/2" ThunderHex shaft from VEX Robotics
(optional) Plastic Safe Lubricant for gears (silicon, PTFE, white lithium grease, etc)
Starting with the gearbox back, look inside and you will see a hex opening that will fit a #8 nut. Place a #8 nut in the hole. Using the motor terminals as a guide, insert the Denso motor on the outside of the gearbox back. Place a lock washer over the #8-32 x 3/4" bolt and lightly screw it into the hole containing the nut. Don't tighten the screw until all screws are in place.
Now place the 1/4" shaft into the 1/4" hole inside the gearbox back and place one of the brass washers over the shaft. Now press fit the brass bushing into the gear with the 5/16" hole. It should fit snugly. If not add some tape to the bushing and insert it. Now place the gear over the 1/4" shaft so the plastic gear mates with the motor gear. Place the second brass washer over the 1/4" shaft onto the gear.
Press one of the HEX flange bearings into inside opening of the gearbox back. Place the ThunderHex shaft into the bearing. Place the second gear over the ThunderHex shaft starting with the non-gear side. The first and second gears should mesh well. Place the second HEX flange bearings onto the ThunderHex shaft starting from the flanged side.
Crimp the 0.187" Female Terminals to the ends of 16 - 18 AWG stranded wire. These will be your connection to the motor. The motor draws 7A at stall so 18 AWG wire or larger is all that is needed. Once the wires are attached, press the terminals onto the motor terminals.
Now take the gearbox front and mate it with the gearbox back. Place two of the #8-32 x 2" Flat Phillips Countersunk Machine bolt into the holes attaching the motor. Place a lock washer and nut over the end of both screws and tighten down the motor evenly. Place the last Flat Phillips Countersunk Machine bolt in the hole with the counter sink and attach using a #8 washer, lock washer and bolt - in that order. tighten to about the same tension at the motor bolts.
The last three #8-32 Round Head Machine bolt act as both the gearbox mounting bolts as well as bolts that hold the gear box together. The length of the bolts will depend on how you are going to mount the gearbox.
NOTE: you will also need to determine how you will keep the ThunderHex captive to the gearbox. This could be done with a bolt and washer on the motor side, and a hex collar or gear on the other. Since the method used to keep the shaft captive will depend on how you intend to use the gearbox, I leave this as an exercise to the user. Also note, that I have not use any lubricant on the gears yet and it seemed to work just fine. I do intend to find and use a plastic safe lubricant if we end up using the gearbox on our robot.