Introduction: Multi-Purpose AT Grabber
Over the course of this semester, our team has been working with our client, Jim, who, due to a C4-5 spinal fracture, has low dexterity in his arms and no dexterity with his wrists or hands. Because of his injury, Jim has a great deal of trouble picking up fallen objects and has asked us to create a tool to help him complete this task. This instructable outlines the steps of fabrication for this device.
This device is a four-featured multipurpose grabber that will be mounted on to Jim's arm using cuffs and an interface between channels in a rigid mount and the grabber. The four features are a tape dispenser, a magnet, a hook and a spatula.
Step 1: Bill of Materials
For this project you need the following materials and capabilities:
1. 3', 0.75" square aluminum box extrusion
2. 6 qty. - 1" 6-32 flat head machine screws
3. 2 qty. - 1 1/8" 6-32 flat head machine screws
4. 2 qty. - 3/4" 8-32 set screws
5. 4 qty. - 3/4" 4-40 machine screws
6. 8 qty. - 6-32 square nuts
7. 8 qty. - 1/2" OD, 3/8" ID, 1/4" sleeve bearings
8. 3' 3/8" delrin rods
9. 2' 2" x 3" block of wood
10. 1/2" wide spool of double-sided scotch tape
11. Tape blade/cutter
13. 4-40 Tap
14. 8-32 Tap
15. 1/2" diameter, 1/4" deep magnet
16. 3D printer to print ABS or PLA
17. Drill press (power drill also usable)
18. Lathe (optional)
19. Band saw (preferred) or hacksaw
20. 1/4" ABS sheet, 12" x 6"
19. Laser cutter
20. 1/4" acrylic sheet, 12" x 6"
Step 2: Lower-Half Fabrication #1: Aluminum Extrusion Modifications and Attachments
In the final prototype, the lower half of the design is composed of a combination of metal, delrin, screws, and 3D printed parts. All parts were printed on an Ultimaker 2+ in either ABS or PLA plastic.
The main body of the grabber is composed of a 26.5” long (custom to height/length from hand to ground) 0.75” x 0.75” hollow 6061 aluminum extrusion. A 3D-printed cap (file name Al Extrusion End Cap), friction piece (file name friction guide piece), and two guides (file name dowel guide piece) are slid around the aluminum extrusion and are held in place with 1” 6-32 flat head screws. Thru-hole location for the 6-32 screws are dimensioned in Figure 3. Dimensions are in inches. A #26 drill bit can be used to drill these holes. Once the four pieces are slid on and screwed into place, a total of 8 sleeve bearings are inserted into the cylindrical extrude cuts of the two guide pieces (four bearings into each guide piece). The sleeve bearings are 0.25” long with an outside diameter of 0.50” and inside diameter of 0.375”. The guides and bearings are used to ensure that the rods of the four functional elements are properly aligned. In addition, the cap is used to protect the user from the sharp edge of the aluminum extrusion. The friction piece was installed so that there was some resistive force for the poles of each functional part to rub up against. This ensures that none of the functional parts will move in or out when not in use.
1. 3D print Al Extrusion Cap, friction guide piece, and 2x dowel guide piece.
2. Measure the distance from the person's palm to the floor and cut the aluminum extrusion to length based on that. Add 8" to the length of the extrusion to decide the length of the aluminum extrusion. For example if the distance from the palm to the floor is 19" with the person's arm fully extended then cut the extrusion to 27".
3. Drill holes in the extrusion according to Figure 3 above using a #26 drill bit.
4. Slide the dowel guide piece, friction guide piece, dowel guide piece, and extrusion end cap into place (slide onto extrusion in that order).
5. Screw the 3D printed parts to the grabber using the 1" 6-32 flat head screws and the 6-32 square nuts.
6. Insert the 8 sleeve bearings into the cylindrical extrude cuts of the two guide pieces (four bearings into each guide piece).
Step 3: Lower-Half Fabrication #2: Four Function Elements
Next is the design and fabrication of the four function elements. Each element (tape dispenser, hook, magnet, and spatula) is 3D-printed and is connected to a 0.375” diameter black delrin rod that is fed through the guide pieces. A magnet is super glued into the magnet mount. The magnet mount and hook are bound to 8.4” long rods also via superglue. The tape dispenser and spatula are connected to 5.25” long delrin rods via a 0.5” 8-32 set screw that is screwed into tapped holes in either end.
The tape dispenser is composed of several pieces. It is illustrated in Figure 4. The two sides are held together with a 1’’ 6-32 screw and nut. Double-sided tape and a sleeve bearing are placed on guides between the two sides. Tape is wrapped around the bearing and long the front. It can be cut daily by the caretaker with the small grooved metal piece (not depicted). Once all four rods are slid through the guide pieces, end push flaps are screwed into the ends of the four rods with a 0.5” flathead 4-40 screw. The push flaps look like flower petals. Foam padding is added to the back of these flaps for added hand protection. They are cut to proper shape and adhered to the push flaps with epoxy. In regards to functionality, the magnet is very strong and can be used to pick up any everyday magnetic items. This includes all the pens and stylus that Jim uses on a daily basis. The hook can be used with anything that has a string loop (water bottle, brush end, etc.) or flexible cloth materials (shirt, baseball caps, washcloth, etc.). The tape dispenser is great at picking up flat items such as paper. Finally, the spatula is used to push around heavier objects (remotes, books, etc.) that are not used routinely. Through the spatula, these objects can be pushed out of the way and can be later picked up when a caregiver or coworker comes by.
1. 3D print hook, magnet mount, 4x push flaps, spatula, tape holder left, and tape holder right.
2. Cut 0.375" diameter delrin rod to 2x 8.4" long rods and 2x 5.25" long rods.
3. Drill and tap holes into one end of all of the delrin rods for 4-40 screws.
4. Tap holes in the pedal-shaped push flaps for 4-40 screws.
5. Drill and tap holes into the other end of the 5.25" longs rods for 8-32 screws.
6. Tap hole in the spatula and tape holder for 8-32 screws.
7. Screw the two halves of the tape dispenser together with the spool of tape in place in between them using a 1" 6-32 screw and nut.
8. Epoxy the tape cutter piece into the slot on one side of the tape dispenser designed for it.
9. Pull tape out and cut with cutter piece in order to have it in place for use.
10. Screw the assembled tape dispenser and the spatula to the 5.25" delrin rods using the 3/4" 8-32 set screws.
11. Epoxy magnet to the magnet holder.
12. Epoxy the assembled magnet holder and the hook to the 8.4" long delrin rods on the end without a hole.
13. Insert the delrin rods through the dowel guide pieces in the order (working clockwise) spatula, hook, tape, magnet working around the aluminum extrusion.
14. Screw the pedal-shaped push flaps onto one end of all of the delrin rods using 0.5" flathead 4-40 screws.
Step 4: Upper-Half Fabrication
The upper half of the grabber contains the portion for the user to mount and dismount the grabber from his or her arm. This design has the slides on the grabber and the channel on the mount. The slides are installed similarly to the guides on the bottom half of the grabber. They slide onto the ABS sheet and are then screwed into place a depiction of all the screw holes for the cuffs and hooks can be seen in Figure 8.
The slides are spaced exactly 8.5” apart. So similarly, the mount has channels that are 8.5” apart the channels are cut in a way such that they funnel down into sleek long links. They are wider at the opening to account for any potential misalignment of Jim’s arm. In the current design, the mount channel is made out of black ABS plastic but in the ultimate design it could be made out of a 1/4” inch thick laser cut acrylic. Dimensions of this top part of the mount can be seen in Figure 9. The mount is screwed into wooden blocks that are 2 inches in height. This height is to allow for clearance between the table and upper mount channels.
1. 3D print a set of cuffs (wrist+forearm; small, medium, or large) and 2x Slot_Insert_mount - Design X.
2. Drill holes in the the other end of the aluminum extrusion according to Figure 8 using a #26 drill bit.
3. Either laser cut the drawing from Figure 9 into 1/4" acrylic or cut 1/4" ABS into that design using a band saw or hack saw.
4. Slide the Slot_Insert_Mount pieces into place along the aluminum extrusion. They should be placed at the 1st and 3rd sets of holes from the end of the aluminum extrusion.
5. Screw the Slot_Insert_Mount pieces to the aluminum extrusion of the grabber using the 1" 6-32 flat head screws and the 6-32 square nuts.
6. Screw the cuffs into the remaining sets of holes using the 1 1/8" 6-32 flat head screws and the 6-32 square nuts. The forearm (larger) cuff should be towards the end of the aluminum extrusion while the wrist (smaller) cuff should be more towards the middle closer the the lower-half assembly.
7. Drill holes in the ABS according to Figure 9.
8. Cut the 2" x 3" block of wood into one 12" piece and one 4.5" piece.
9. Screw the ABS to the wood using #6 wood screws.
10. Clamp or attach the ABS wood base plate assembly to a table.
11. Place the grabber assembly into the base plate and operate!
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