Repository navigation
Part 4 LRA Housing Assembly
The LRA housing is entirely 3D printed. This page assumes you have the LRAs and the prepared wire leads from Part 3 Building the Tactors — that page covers the LRA and crimping the JST connectors. The wire-to-LRA connection is made here, in Step 2, by the printed wire plug pressing the bare wire ends onto the LRA terminals — there is no soldering. A pair of flush trim wire cutters will be needed to trim the bare wire ends to length. A magnifying desk lamp can be very helpful during assembly.
The LRA housing consists of the following 3D printed parts: LRA sled, wire plug, shell, lid, pin, finger cup, and finger support. There are three pin options to choose from. The non 3-D printed parts are the LRA motor and wire.
The assembly was tested using Bambu Labs P1S and A1 printers. The shell and other hard plastic components should be printed with any rigid plastic including PLA and PETG. The blue finger cups on the right have been tested with TPU 95A and flexible PLA. Other soft and flexible plastics may be used as well. A 0.4mm print head and 0.12mm high-quality layer height should be used. Deviation from these settings may result in parts not fitting properly.
The design uses fit tolerances of 0.2mm. Due to this a smooth print plate is preferred but a textured plate is also acceptable.
The wires powering the LRA are held in place using a printed wire plug. It is designed to have a tight fit to ensure good electrical contact and provide strain relief for the wire. This is a step where a magnifying desk lamp can be very helpful as the assembly is small.
The wire plug has a horizontal slot which the wire insulation is pressed into. It ends in a vertical slot that the wire is fed through.
Insert the bare wire ends through the slot until the wire insulation is flush with the bottom of the plug.
Bend the bare wires around to each side of the plug and into the vertical side slots.
Bend the insulated wire down until it rests in the horizontal notch of the wire plug. The bare wires should be flush with the top of the plug. If they are too long they must be trimmed until they are flush.
If the wires are too short they may not stay in place. This could result in the wires contacting each other causing a short circuit. The wires must be long enough to stay in the pockets.
Insert the LRA into the LRA sled at an angle sliding forward until it stops then pressing down gently on the edge until it is fully seated. The LRA should now be flush with the top of the LRA sled like the unit shown in the back of the photo.
Begin inserting the wire plug into the LRA sled with the bare wire facing down to make contact with the LRA and the insulation pointing up. This is a snug fit and will require slow but firm pressure. Ensure the bare wire remains in the side slots of the wire plug during insertion as shown in the photo. If the bare wire sticks up past the top of the wire plug, use flush trim wire snips to trim it flush or the plug will not be able to fit.
Once the bare wire is positioned correctly finish pressing the plug into place until it is flush with the back of the LRA sled. The LRA sled on the right has the plug partially inserted, the one on the left is fully inserted.
The lid assembly consists of three parts, the pin, the lid, and the finger cup. The lid and finger cup use dovetail joints which must be slid together until fully seated before inserting the pin.
There are three pin options, a short, standard, and long pin, each approximately 0.5mm different in length. These can be changed out to customize the fit. Start with the medium length pin. Once the gloves have been worn for a session pins can be changed out if needed.
To assemble the lid and finger cup, slide the lid into the dovetail slots with the lid's locking tab facing towards the pin hole in the finger cup.
Once fully seated the holes should be centered on each other. Misalignment of these holes may cause the pin to bind and reduce the vibration felt from the LRA.
Insert the pin into the lid assembly from the lid side so the top points out of the finger cup and the pin flange is seated in the lid. Set the assembly aside.
Caution
Buzz-check before you close it up. The dovetail joint in Step 4 is difficult to reverse without risking the latching tab. Before going any further, plug the LRA sled's JST connector into an open motor port on a board that already passed its Part 2 Flashing and Smoke Testing the Bare Board smoke test and, in BuzzahBuddy's Calibration screen, tap the finger button for that port (see the finger-to-port table in Part 6 Wiring the Glove Harness) in the row for that board's role. Confirm you feel a strong, consistent buzz before committing the sled to the shell.
The LRA sled uses three springs to support the unit inside the shell. The springs sit in pockets on the LRA sled and are centered on pins inside the shell. This is best done with the LRA sled lying face down as shown in the photo. The springs tend to nest inside one another. Verify that only one spring is installed per pocket of the LRA sled. Ensure the pockets on the LRA sled have printed round and smooth by pressing down on the springs and confirming they are able to compress and extend freely. If the pockets are not round and smooth a small file, pen knife or sand paper may be used to smooth and round the holes.
Once the springs are installed and moving freely, set the shell on top of the LRA sled with the wire notch on the same edge as the wires and gently flip the unit over while supporting the LRA sled to keep the springs in place. This may also be done by holding the LRA sled and springs upside-down on a finger tip. Set the shell over the LRA sled then gently pinch the units together to flip them over before setting them down.
Press down gently on the LRA sled. The unit should move up and down freely. If any grinding sensation is felt or the unit does not move freely flip the unit back over and remove the shell to verify the springs are still properly seated. Carefully reassemble ensuring the springs remain in place centered over the alignment pins in the shell.
The lid assembly installs onto the shell using another dovetail joint. The lid is inserted by sliding the latching tab end into the dovetail slots at the wire notch end of the shell. This image does not show the finger cup or pin for clarity.
To assemble, hold the lid assembly in one hand and the shell assembly in the other. Tip both units sideways while pinching the pin in the lid, and the LRA sled into the shell, to ensure they remain seated. Gently slide the lid assembly into the dovetail slots of the shell ensuring the pin does not catch on the shell. Slide the assembly forward until it is mostly seated but has not latched.
The rear finger support may now be installed. It is inserted into the dovetails on the finger cup in the same manner as the lid. Lift the insulated wires out of the way and slide the finger support into the finger cup with the thicker end towards the shell. Ensure both dovetail joints are properly seated as it is possible to have only one in and the other free.
Once the finger support makes contact with the lid, pinch the back of the finger support and the front of the shell towards each other until the latching tab on the lid snaps into place on the shell.
The unit is now fully assembled. During assembly the finger cup may have shifted towards the latch at the front of the shell. To ensure proper placement hold the shell while pushing the rounded end of the finger cup back towards the wire until there is no movement.
Press down on the pin and release it to ensure the pin moves freely. If the unit needs to be disassembled gently lift the latching tab at the front while pushing the lid towards the rear of the shell. Excessive force will break this tab. Use slow but firm pressure until it releases.
The slots and brackets on the side of the housing are designed for securing the housing to gloves to keep the unit in place. Small zip ties will fit but other methods may be used as well.
Next: Part 5 Mounting Tactors in Glove Fingertips | Previous: Part 3 Building the Tactors | Back to: Home