The following parts are required to assemble the gripper.
- (1x) Base
- (1x) Base attachement
- (1x) Gear finger right
- (1x) Gear finger left
- (1x) Outer finger right
- (1x) Outer finger left
- (1x) Central finger right
- (1x) Central finger left
- (1x) End finger right
- (1x) End finger left
- (1x) finger tips, multiple options possible:
- Without pads:
- (1x) finger tip left
- (1x) finger tip right
- With thin pads:
- (1x) finger tip pads left
- (1x) finger tip pads right
- With thick pads:
- Without pads:
- (1x) Dynamixel AX-12A Servomotor
- (1x) USB2AX
- (1x) Voltage regulator (step-down) LM2596 boards. The boards are cheap and easily findable online, but they should have the following dimensions to fit within the case.
- (18x) Ball bearing 10x4x3mm
- (2x) Extension spring (length max of 50mm at rest, diameter max of 8.5mm)
- (12x) M3 inserts (M4 outer diameter)
- (7x) M3 nuts
- (8x) (optionally self-locking) M3 nuts
- (12x) M3 x 16mm hex socket head screws
- (8x) M3 x 20mm hex socket head screws
- (2x) M3 x 5mm hex socket head screws
- (1x) M3 x 25mm countersunk head screw
- (7x) M5 x 8mm hex socket head screws (for attaching to the HEBI actuator)
- (6x) M2 x 10mm screws (for fastening servomotor)
- (6x) M2 nuts (for fastening servomotor)
- (4x) M2 x 5mm screws (for fastening on servomotor's ouptut shaft)
- (3x) Zip ties
- (1x) Molex minifit Jr. male housing (2x1) and its associated crimp terminals (for connecting with HEBI Robotics Arm power supply)
- (2x) Mini-SPOX 2.50mm female housing (3 pins) and its associated crimp terminals (for connecting with the Dynamixel AX-12A servomotor, check Dynamixel servomotor documentation for more information)
- (1x) male & female connector (and associated crimp terminals) with at least 3 pins, small enough to fit inside the gripper. Here, a 2x2 Molex Microfit is used.
Most parts were printed using Ultimaker black/red PLA and/or black tough PLA with PVA supports (dual-printcore printer). The PVA support material is disovable in water and allow for a high precision in the printed connector housings. It's probably possible to print the parts without the PVA support material, but that would require more post-processing to remove the supports.
The following printing parameters were used for all parts printed in PLA:
| Parameter | Value |
|---|---|
| Layer height | 0.15mm |
| Infill | 50% |
| Infill pattern | cubic subdivision |
| Support material | PVA |
| Support pattern | triangles |
| Support overhang | 45% |
Add the inserts in the attachment part. Use a soldering iron is needed.
Clip in the USB2AX.
Solder the required wires on the DC power supply. It is also a good time to adjust the voltage output for the servomotor (between 9V and !"V, ideally 11.1V).
It can be then screwed in place using M3x5mm screws. On the other end on the input wires, crimp the minifit male housing connector, so that the gripper can be plugged to the HEBI Robotics power supply.
Prepare the output cable of the USB2AX by crimping a mini-SPOX connector. Only the two side wires should be connected, not the middle one, since power will be provided by the DC power supply.
Connect the cable and ziptie it with the power output wires.
Respecting the connector pins, crimp the output power sypply ground and the USB2AX output ground together. Connect the ground, data output wire and power supply positive wire in a connector (here a Molex microfit).
On the other main part, prepare a cable that will be connected to the servomotor. Crimp a mini-SPOX connector on one side and the complementary connector (here a Molex microfit), respecting the wiring of Dynamixel AX12-A servomotor. Fasten the cable against the part using zipties.
Insert the M3 nut under the part.
Put the servomotor in place, sliding it from under, and fasten it using M2x10mm screws.
Prepare the right geared finger by mounting the 2 ball bearing on its axle, one on each side.
Slide the finger in place and fasten it on its axle using a M3x25mm countersunk head screw.
Put the servomotor to its 0deg position (512 in step command). This cam be done manually by turning the ouput shaft of the servo until the mark on the shaft aligns with the one on the servomotor body. The recommended and more reliable approach is to power the servomotor, plug to the USB, and use the Dynamixel Wizard to command the servromotor to the 0deg (cmd 512) position.
Then screw the left geared finger on the servomotor with M2x5mm screws, making sure the left and right finger are aligned at the same angle.
Screw the spring in place on both geared finger, using a nut on the other side.
Add M3 inserts in the finger end parts, using a soldering iron if needed.
Assemble the rest of the fingers. For every pivot the method is the same. On the inner part, place a M3 nut. It might be needed to force it place but be careful if using a soldering iron, as it should not be pushed deeper than its housing.
On the outer part, place a ball bearing on each side, from the interior. It might be need to push with a screwdriver or so to lock it in place.
Slide the outer part on the inner one. It is normal if the assembly is tight and difficult to align.
Fasten an M3x20mm screw in the pivot. Fasten on the other side an additional (optionally self-locking) M3 nut.
Repeat the procedures for all finger, screw the other end of the springs in place and voilà! The gripper is assembled. Please refer to the main readme for mounting on it on a HEBI actuator and changing the finger tips.