Build a Robust and Modular Helper Arm

This tutorial will show you how to build all the components of my modular helper arm system. The arm is designed to be almost entirely 3D-printed, using minimal metal hardware. It is also designed to be robust and versatile, thanks to its modular design and the variety of tools available.

Currently, the system consists of three types of bases:

1. Conventional table-mount bases
2. A switchable magnetic base (building tutorial available here)
3. A suction-mount base for smooth surfaces (building tutorial available here)

The system uses a modular arm whose length can be adjusted by adding or removing ball-joint links. It is designed to reliably support loads of a few kilograms when extended to approximately 1.2 meters.

Finally, the system includes several tool attachments, including:

1. A universal phone holder
2. A camera mount
3. A vice

This tutorial will first introduce all of these elements to help you decide what you want to build. It will then show you, step by step, how to assemble them.

The list of supplies you will need for this project depends on the modules you decide to build, so I have included a list directly in the first step related to each module.

Almost all of the required parts are standard bolts and nuts, which you can easily find with a quick search from your favorite hardware supplier. Only the 3 mm-diameter rods (used for the phone holder and the vice) and the M3 heat set inserts with a 4.2 mm outer diameter and 4 mm thickness (optional for the arm) are somewhat less common. I have therefore included a few links below to help you source them. I do not endorse these suppliers; the links are provided for reference only.

1. 3 mm rods: Taobao, Aliexpress, Amazon
2. M3 melt inserts 4.2 mm OD and 4 mm thick: Taobao, Aliexpress, Amazon

The bases:

The most versatile base type for this arm is the table-mount base, as it can adapt to almost any table. There are two versions: the "small" version for tabletops up to 18 mm thick and the "large" version for tabletops up to 30 mm thick. While I use PLA+ for its toughness and ease of printing, you can print the base using PLA, PETG, or ABS. For optimal grip, the base also requires TPU pads. Besides the 3D-printed parts, you will only need a few M3 bolts and nuts.

In labs or workshops, the switchable magnetic base is also very useful. There are two versions, using either 10 or 20 magnets with a diameter of 12 mm. The fabrication steps are described in this Instructable. With the 20-magnet version supporting more than 5 kg, this base is very convenient for use on optical breadboards or on the metal surfaces of workshop machines.

Finally, the suction-cup base can be convenient for mounting a recording device on windows, glass tables, or plexiglass shields. Printing a reliable suction cup out of TPU can be challenging, but you can follow this Instructable for a step-by-step guide.

The arm:

The arm is modular by design. It is composed of a minimum of one "ball-joint base" and one "ball-joint top link," but you can extend it as desired by adding as many "ball-joint links" as needed for your application. Each link contains its own captive nut and can be printed independently. I recommend keeping a few extra links on hand in case you need to extend the arm later.

The tools:

The phone holder is very handy for taking photos and videos. It exists in two versions. The small version can hold most phones as long as they do not have thick protective cases, while the large version can accommodate even relatively thick phone cases. Besides the 3D-printed parts, it requires one M5 bolt, a few M3 bolts and nuts, and two 3 mm-diameter metal rods.

The camera mount uses a 1/4"-20 UNC bolt and is compatible with accessories using this standard. Designed for robustness, it can handle loads of a few kilograms.

The vice is a basic universal tool, but this version has a few twists. The screw uses a long pitch multi-thread for quick adjustments, while the knob includes a cranking feature to ensure secure locking and repeatable tightening. It also uses 3 mm-diameter rods for smooth sliding and to ensure that the jaws never jam.

To build a table-mount base, download the print files from Thingiverse, Printables, or MakerWorld and import them into your slicer. The small base version can be used for tabletops up to 18 mm thick, while the large version can accommodate tabletops up to 30 mm thick. If your table is relatively small, the small version will save some filament and, more importantly, provide greater rigidity.

I used TPU for the pads to increase friction with the tabletop and PLA+ for the rigid parts. PETG and ABS are also suitable, while PLA works but is less durable. I recommend printing all rigid parts with a 0.2 mm layer height, 5 wall lines, and 25% infill. Some supports are required, as shown in the illustration. The printing orientation is optimized for part strength at the expense of thread quality, but the threading is specifically designed and tested to function reliably with this printing orientation. The pads should be printed with 60% infill.

Besides the printed parts, you will need four M3 screws, 15 mm long, and four M3 nuts. The bolts used to attach a tool to the base are not included in this count.

Once you have gathered all the parts, start by installing the knobs onto the screws and securing them with M3 bolts. Do the same with the "screw tip" on the opposite side, and tighten the bolt just enough to allow the screw tip to rotate freely.

Then insert M3 nuts into the base. You can easily do this by inserting a long M3 bolt from the top side, attaching the nut to it, and tightening until the nut reaches the bottom of the hole. Then insert the eight TPU pads into the base and onto each of the screw tips. Insert the screws one by one into the holes and force them in once or twice to break them in and remove any small burrs. You will find that even if the fit initially feels very tight, it eventually produces a very smooth action.

At that point, you can attach your favorite tool and start using this base.

To build the arm, you will need one "ball join base", one "ball join top link", and as many "ball join links" as you want in between. The "ball join top link" exists in two versions: one using 4.2 mm OD, 4 mm thick M3 heat-set inserts, and the second using M3 nuts. The "ball join base" plus "ball join top link" assembly measures 60 mm, and each "ball join link" adds 65 mm to the arm. They can be assembled and disassembled very quickly by simply unscrewing the nut on each link.

To build it, simply download the STL files from Thingiverse, Printables, or MakerWorld and print as many as you need. The STLs are pre-oriented, and the captive nuts are positioned to print in place. All parts except the top links can be printed without supports, and the threading is designed to work with fairly rough printing parameters. I recommend using 0.24 mm layer height, 3 walls, and 25% infill to achieve relatively fast print times. If rigidity is more important to you, you can use 5 walls instead.

Once printed, just install the heat-set inserts or M3 nuts in the top link, and your arm is ready to go. You will only need 4x M3 bolts to attach it to a base. The bolts should be 10 to 16 mm long if you use the table mount base, or 5 to 8 mm long if you use the magnetic or suction cup base.

The phone holder is available in standard or XL size. The standard size can fit any phone without a protective case and most thin cases. If you use a thick case on a large phone, consider using the XL size.

To build it, you will need:

1. 2x 3 mm metal rods, 90 mm long for the standard version and 100 mm long for the XL version
2. 1x M5 nut
3. 1x M5 bolt, 20 to 28 mm long
4. 5x M3 bolts, 15 mm long
5. 4x M3 bolts, 10 mm long, to attach the phone holder to the arm or base

To start the build, download the STL file for the version you want from Thingiverse, Printables, or MakerWorld, and print it. The STLs are pre-oriented, and I recommend using a 0.2 mm layer height, 4 walls, and 25% infill. Some parts require supports.

Once you have all the parts, start by inserting 2x M3 nuts into the main body. Then use two 15 mm M3 bolts to attach the arm to the main body.

Place both jaws onto the screw and tighten it fully. The jaws should be aligned with each other. If they are not, remove one jaw, rotate it half a turn, and tighten it again. When both jaws are in sync, open them slightly and position them on the main body. Use the screw retainer to secure the assembly in position with two more 15 mm M3 bolts. Add the adjustment knob to the end of the screw and secure it with the last 15 mm M3 bolt.

Insert the two 3 mm rods from the side of the assembly and push them in until they are flush with the surface. If necessary, you can place a drop of glue in the hole in the central part of the main body to hold the rods in position. Place the M5 bolt into the fixation knob and the M5 nut into the base. Use it to attach the phone holder and adjust its tilt.

You can use four 10 mm M3 bolts to attach the phone holder to the arm or directly to one of the bases.

To build the camera mount, you will need:

1. 1x 1/4"-20 UNC bolt, 18 to 20 mm long
2. 1x M5 nut
3. 1x M5 bolt, 25 to 30 mm long
4. 4x M3 bolts, 10 mm long, to attach it to the arm or base

To start the build, download the STL file for the version you want from Thingiverse, Printables, or MakerWorld, and print it. The STLs are pre-oriented, and I recommend using a 0.2 mm layer height, 5 walls, and 25% infill. Some parts require supports.

Once you have all the parts, insert the 1/4" bolt into the camera knob. To avoid confusion, the camera knob is engraved with a " 1/4'' " marking. Then insert the bolt into the fork and install the retainer. Screw the retainer in until it sits in the recess in the fork. Then add the M5 bolt to the adjustment knob and the M5 nut to the base. Use it to attach the base to the fork and freely adjust the orientation.

The mount can be attached to the arm or directly to one of the bases using four 10 mm M3 bolts.

The vice is available in two versions: the small vice, which is suitable for holding objects up to 40 mm in size, and the large version, for objects up to 75 mm in size. I plan to design a version with interchangeable jaws, but it is not available yet.

To build it, you will need:

1. 3x 3 mm metal rods, 65 mm long for the small version and 100 mm long for the large version
2. 1x M3 bolt, 15 mm long
3. 4x M3 bolts, 6 to 8 mm long, to attach it to the arm or a base

To start the build, download the STL file for the version you want from Thingiverse, Printables, or MakerWorld, and print it. The STLs are pre-oriented, and I recommend using a 0.2 mm layer height, 5 walls, and 25% infill. Some parts require supports, as shown in the illustration.

Once you have all the parts, insert the screw into the main body and add the printed washer.

Then add the knob to the end of the screw and secure it in position with the M3 bolt. Tighten it until there is no play, while still allowing the screw to rotate easily. Insert the jaw from the open side and screw it on. Add the three 3 mm rods and push them in until they are flush with the body. The vice is then ready. You can secure it to the arm or to a base using four 6 to 8 mm M3 bolts.

This vice uses a wave pattern on the knob and main body to create a clicking effect when tightening. This effect helps the vice maintain its clamping force even when exposed to strong vibrations, and helps provide a more consistent clamping force each time you use it. The strength of the clicking effect depends on the printed washer. Without the washer, the knob is completely jammed and the vice is unusable. With a 0.2 mm thick washer, the clicking effect is discreet and occurs when fairly significant pressure is applied to the vice. If you want a stronger clicking effect, you can print the washer with a lower thickness, or cut one out of thin, rigid plastic.