The drill we use for the U-Build Bionic Knee is the Makita XFD11. It has been discontinued, so you will need to search ebay in order to find one. It is important to note that other drills are not compatible with this project. Make sure you have the correct drill. The Makita XFD11 driver drill must be disassembled to access the components used in this project. Before disassembly we recommend that you use the drill as a tool to help on all parts of the U-Build Bionic Knee where it would be helpful, such as screwing in any fasteners or securing the prosthetic adapters onto the aluminum stock metal for the bypass.
Follow the instructions to disassemble the drill and set up the transmission so it is back-drivable. After you have disassembled the drill, you'll need to cut a hole at the end of the transmission. Follow the instructions below on how to cut a hole for a machine key to hold a gear in place.
Drill Disassembly Video
Drill Disassembly Instructions
Step 1: Remove battery from the drill to ensure it doesn't turn on while you are taking it apart.
Step 2: Use a flathead screwdriver to remove the screw in the center of the drill. This screw is reverse threaded, meaning to loosen it you will need to turn the screw in a clockwise direction. This may require a lot more force than shown in the video above.
Step 3: A lot of force will be required to break the seal on the chuck of the drill. As seen in the video, we can use the power of the drill to do this. Insert a large Hex key wrench into the chuck of the drill and tighten it. Find a sturdy surface, like a cement step, as well as something to soften the impact, like a piece of cardboard, so the wrench isn't damaged. Increase the torque to 20 and set the speed of the drill to level 2. Make sure the drill is set to the correct direction depending on which orientation you have set up. Replace the battery and securely hold the drill next to the surface being used. Turn it on for a half rotation or until it hits the step. Repeat this process until the seal breaks and the drill no longer rotates when the trigger is pressed. Remove the battery and wrench after this is completed.
**Note: This generates a lot of force. USE OF GLOVES AND SAFETY GLASSES IS HIGHLY RECOMMENDED. Keep hands clear of the wrench when it is in the drill. Make sure the drill is held securely when operating.**
Step 4: Take apart the drill. Unscrew the chuck and remove the adjusting ring. Keep the ring on hand since it is helpful to retighten the gear box later. Remove all eight housing screws to open the drill housing and remove the interior components. Separate the gear box from the rest of the assembly.
Step 5: Open the gear box by unscrewing the metal ring on top. The adjusting ring may be useful for this step. Remove the three rings and small metal insert from the gear box. Carefully take the top half of the gear box off and remove the three cylindrical needle nose bearings from the clutch.
Step 6: Reassemble by replacing the top half of the gear box and each of the three rings. Don't replace the metal insert although this is contrary to what's shown in the video above. If the components were moved during disassembly, then it will be hard to reassemble the gear box without reorienting them. The picture shown has the correct orientation for both the bottom and top halves. Make sure the gear box is screwed together tightly and place back onto drill motor. The adjustment ring can be used to help tighten the metal plate back onto the gear box.
Step 7: Hot glue the long metal bar down to the gear box. If the bar is in any other position the gears will not rotate as smoothly, so we want to ensure it stays down.
How to Cut the Key Slot
In order for the gear to stay in place on the end of the transmission, you must insert a rectangular machine key between them. The gear already has a rectangular cavity (key way) to accommodate this, but the thread on the end of the transmission does not. You must cut this yourself using a Dremel. The cut should be just deep enough that the key sits about halfway in. Cut as far up the end of the transmission as you can. We used a cut-off wheel attachment for the Dremel and the smaller diameter you can get the easier this will be. Only cut a small amount at a time to ensure you do not cut too much and that the key is not too loose in the slot. Reference step 7 in the Transmission page to determine if slot is correct size.