Robotic Arm Gripper

I created this robotic arm gripper for an assignment in Design 178 Wearable Technology at UC Davis. We were tasked with creating a piece of wearable technology that helps to solve some kind of issue. I wanted to create this gripper to extend the reach and capabilities of the human body.

Supplies that will be needed:

1. 1/4" plywood (can be thicker but shouldn't be thinner)
2. saw
3. 3 aluminum channels
4. Screws (comes with aluminum channels linked below)
5. Adafruit Bluefruit (Should work with non-Bluetooth model, but have not tested it)
6. Flex Sensor
7. Micro Servo
8. Continuous Servo
9. Limit Switches
10. Breadboard
11. Foam
12. Hot Glue
13. 3D Printer
14. Glove
15. Rubber Bands
16. Wires
17. Soldering Iron
18. Solder
19. Velcro straps (for arm and battery)
20. Staple Gun
21. Epoxy (I used Gorilla ultimate Epoxy)
22. Metal axle (I used one from a toy car, but it was approximately 1.75mm)

Links:

-Aluminum channels with screws: Amazon.com: QWORK 12" T-Track, 4 Pack Aluminum Double Track with Mounting Holes for Woodworking : Toys & Games

-Limit switches: HiLetgo 10pcs Micro Limit Switch KW12-3 AC 250V 5A SPDT 1NO 1NC Micro Switch Normally Open Close Limit Switch with Roller Lever Arm Black: Amazon.com: Industrial & Scientific

-Micro Servo: Micro servo [TowerPro SG92R] : ID 169 : Adafruit Industries, Unique & fun DIY electronics and kits

-Continuous Servo: Continuous Rotation Servo [FeeTech FS5103R] : ID 154 : Adafruit Industries, Unique & fun DIY electronics and kits

-Adafruit Bluefruit: Circuit Playground Bluefruit - Bluetooth Low Energy : ID 4333 : Adafruit Industries, Unique & fun DIY electronics and kits

-Flex Sensors: SpectraFlex Flex Sensors | Spectra Symbol

The first step will be to 3D print everything. I included both STL and Fusion 360 files. This will let you adjust the sizing of things such as the holes in the gears if you use a different size axle. I will also link the video I used as reference for creating the rack and pinion design.

(136) How to Design a Rack and Pinion Assembly in Fusion 360 - Part 1 - YouTube

Rack and Pinion Part 2 - Fusion 360

P.S. Before getting too far into the steps, refer to the last step "Usage." This will help to understand how it works and make the steps easier to understand at times.

Next, you will need to download the code onto the circuit board.

Make all connections for the circuit board, motors, flex sensor, and limit switches. Adhere to the wiring diagram.

Now we can begin building the arm. First screw in 2 of the aluminum channels parallel to each other, the third channel sits upside down and within the grooves on the sides. I used this mechanism to space out the channels.

Then the wood needs to be cut. I did not use specific measurements for the cuts, I just used the aluminum channels as a guide for my saw and it contained this spacing.

On the opposite side, attach some foam with hot glue. I also coated the screws with hot glue for extra protection.

P.S. I ended up adding more foam to complete the width of the wood.

I did this step later, but it would have been better to do it at this stage of the build. Use the staple gun to secure the Velcro straps for your arms. The aluminum channels stop the staples from going all the way through, so use the extra channel as backing when stapling the straps. This is also when you can hot glue the Velcro strap for the battery (orange strap).

I hot glued these pieces together, but they could also be remodeled to be one piece.

It will be easier to fit the axle, and motors into their holders before securing them onto the arm. The motors are just friction fit, while the axle is hot glued in. I created a breadboard holder to fit the board I had, and I was given the Adafruit holder, but any file you can find should work.

P.S. The micro servo holder was very tight, and I had to sand it a bit.

WARNING: Epoxy is toxic and needs to be handled with care. Please pay attention to the instructions on the bottle and use proper protection.

Apply the rack, and micro servo holder to one of the aluminum channels not screwed into the wood. Have the rack sit on the right side of the channel. Center the servo holder over the channel and align the front edges. Then apply the small triangle piece to the right side. (may have to wait for the top parts to dry before turning over)

The continuous motor holder, limit switch holders, circuit board holder, and breadboard holder can all be hot glued to the wood. There are not any specific measurements for placement, but the image of the finished product should give you a good idea.

The switches can get tricky with fitment if you do not figure it out beforehand. Test it and make sure the top aluminum channel slides well with the switches in place. I had to cut a bit of excess epoxy to get it to slide properly. Also be sure the triangle stopper is in between the two switches. These switches work by reversing the motor a bit, so make sure you have the right switch in the right spot.

I simply used rubber bands.

Construction is complete, to use the arm it first needs to be extended. Buttons "A" and "B" on the circuit board are programmed to move the arm back and forth. Button "B" should move it outward, and button "A" should bring it back in. When the limit switches are hit from the triangle stopper, it will slightly reverse the direction and stop. This is to stop it from moving too far in any direction. The flex sensor can be bent to control the micro servo. The grippers are removable, so I recommend angling them far back when the flex sensor is straight.