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Bob Johnson’s full-size claw machine for the Nashville Mini Maker Faire shows how a collection of salvaged mechanisms and fabricated parts can become a working arcade-style crane. The project, featured by Hackaday on September 14, 2015, used an aluminum-angle gantry, skate-bearing slides, printed brackets, a motorized claw and a microcontroller. It is a useful design showcase—not a complete set of plans: the project page lists no downloadable files or formal instructions.
For builders, the main lesson is to design around what can be measured and made reliable, rather than assuming every part must be new—or that every scrap part is suitable for a moving, public-facing machine.
What the original project built
This was a full-size arcade-style crane, not a tabletop grabber. Its cabinet enclosed a prize area beneath an overhead gantry. A carriage moved the claw across the playfield, while a separate lift lowered and raised it. Player controls, colored LEDs and a microcontroller completed the arcade presentation. Hackaday identifies the build as Johnson’s Nashville Mini Maker Faire project and describes its aluminum-angle structure, custom slides, printed mechanical parts, claw mechanism and Teensy LC controller: Hackaday’s project feature.
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The public records do not provide verified cabinet dimensions, motor torque, lifting capacity, cycle time or performance figures. The machine is best understood through its architecture and design choices, not as a blueprint that can be copied to scale.
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What “parts on hand” meant
The phrase does not mean the machine was made entirely from free scrap. The project inventory mixes salvaged equipment, purchased parts and custom fabrication. Its listed contents include copier power supplies and bearings, printer motion hardware, salvaged motors and switches, as well as purchased stepper-driver boards and a joystick. The Hackaday.io component inventory is the clearest public record of those items, though it does not resolve every conflict with the feature article.
| Category | Documented examples | What that means for a recreation |
|---|---|---|
| Salvaged | 24-V and two 5-V supplies from an old copier; printer chassis and belt mechanism; stepper motors; limit switches; copier ball bearings; computer case; miscellaneous wiring. | Reuse can reduce cost, but inspect condition and verify ratings before putting parts into service. |
| Purchased | Three A4988 stepper-driver boards listed as purchased from Pololu; a commercial-style joystick. | “Parts on hand” still allowed for buying components where needed. |
| Fabricated or adapted | Aluminum-angle frame; scratch-built Z-axis stepper mount; 3D-printed motor brackets and pillow blocks; custom claw. | The project depended on fitting and making parts, not simply assembling a box of salvaged components. |
| Inconsistent public descriptions | The feature names a Teensy LC and servo-driven claw; the inventory lists a PIC16F870 and describes a claw designed around a 24-V solenoid. | The available descriptions do not establish whether these are different revisions or inconsistent records. Do not treat both controller or actuator descriptions as one confirmed final configuration. |
How the gantry moves the claw
A crane game needs three controlled motions: X for left-to-right travel, Y for front-to-back travel, and Z to lower and raise the claw. In the 2015 feature, aluminum angle and skate bearings form improvised linear slides. The project inventory separately lists a printer chassis and belt drive for an axis, copier bearings, salvaged stepper motors and a scratch-built Z-axis mount. Together, these records suggest a design assembled from mechanisms with different origins rather than a uniform commercial rail system.
Cabinet frame
└── Y travel: gantry moves front to back
└── X travel: carriage moves left to right
└── Z travel: claw lowers and risesThe useful engineering principle is to match the parts to the load and geometry. A rigid frame keeps the guides aligned; a belt, rail, bearing arrangement or slide guides travel; and a light moving carriage reduces the work demanded of salvaged motors. Before powering anything, the whole assembly should move freely by hand. Limit switches should stop travel before a carriage can strike the frame, and motors, belts and wiring need accessible adjustment and service points.
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The cabinet is a structural part of the motion system. If it racks or twists, the gantry can bind, belts can track poorly and the claw can miss its intended position. Dimensions should follow the actual materials and mechanism, but alignment cannot be left to chance.
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- Brace the cabinet so repeated control use or a player leaning on it does not distort the frame.
- Keep opposing guides parallel and the gantry square; check alignment across the full travel.
- Support clear panels securely and guard moving parts against access.
- Provide a service door or removable panel for wiring, motors, belts and adjustment points.
- Reserve space for power supplies and cable movement, and keep the prize chute reachable.
- Make the base stable enough for repeated operation and the intended setting.
A reuse-first build may have its dimensions dictated by available sheet goods, framing stock and panels. That can be practical, but available material should shape the cabinet only after the required playfield, gantry travel and service access are accounted for.
Design the claw and lift as their own mechanism
The claw is not just an attachment at the end of the gantry. It needs a centered suspension, a lifting cable or rope, a spool or winch that winds consistently, and a way to open and close the fingers. A guide helps prevent the cable wandering; springs or another return mechanism may be needed, depending on the actuator. Travel limits should prevent the claw from striking the floor or over-winding the lift.
The original claw’s actuation is not consistently described in the public records: Hackaday calls it servo-driven, while the inventory describes a scratch-built design around a 24-V solenoid. The available documentation does not settle whether these refer to separate revisions or a reporting inconsistency. A recreation should choose an actuator only after considering its force, duty cycle, supply requirements and safe failure behavior.
Choose prizes for the mechanism rather than guessing from a commercial machine’s grip settings. Test mass, shape, center of gravity, surface friction, fit between the fingers and ability to pass through the chute. Lightweight prizes are a more sensible starting point for an improvised lift than dense objects. No lifting capacity is established for Johnson’s build.
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Plan the controls, power and fault behavior
The documented inventory includes a joystick, stepper drivers, stepper motors, limit switches, multiple power supplies, RS-232 connectivity and an HC-06 Bluetooth module. The feature instead identifies a Teensy LC controller; the inventory names a PIC16F870. Since the records conflict, they should be attributed separately rather than combined into a definitive bill of materials. The exact original firmware, pinout, acceleration settings and code are not verified in the published coverage.
For a new build, separate motor power distribution from logic and accessories, use compatible signal grounds, fuse power outputs close to their supplies, and secure moving cables with strain relief and a controlled loop or cable carrier. Enclose mains-voltage connections; do not treat an aged salvaged supply as safe merely because it powers up. A suitable emergency cutoff should remove motion power, and limit switches should be tested as safety inputs rather than assumed to work because they appear in the inventory.
Use a state machine so a button press cannot issue unrestricted motor commands. A reasonable modern sequence is:
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- MANUAL_XY_MOVE: Allow joystick travel only within the axis limits.
- LOWER: On drop-button press, lower the claw to a controlled endpoint.
- GRIP: Actuate the claw for the chosen mechanism and timing.
- LIFT: Raise the claw while monitoring travel and faults.
- RETURN_TO_CHUTE: Move the gantry to the release position.
- RELEASE: Open the claw over the chute.
- RESET: Return to a known ready condition.
- FAULT: Stop motion and require an intentional reset before resuming.
This is a recommended control structure, not a description of Johnson’s original firmware. Consider limit-switch failure, a stalled lift, a player holding a direction against a stop, interrupted power mid-cycle, a controller reboot, uneven cable winding and a jammed prize. The safe default is to stop movement, remove motor power and leave the machine accessible to an operator.
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- Dual-Layer Play: This claw crane machine features a stacked design combining claw and grabber modes. Place different types of toys with separate difficulty settings, saving space. Easy-to-use controls and a clear display suit all ages
- Adjustable Difficulty: The claw grip adjusts for toys 1.57-3.15 in/40-80 mm, while the grabber mode handles prizes up to 0.11lbs/50g. Smooth, lag-free operation ensures precise, fun gameplay, with success depending on player skill
- Dynamic Lights & Sounds: This toy claw machine offers immersive arcade-style music and colorful lights. Adjustable volume and a 100W motor provide stable, energy-efficient performance for nonstop at-home entertainment
- Sturdy & Stylish Build: Made with a carbon steel body and clear acrylic window, this commercial claw machine is long-lasting and visually appealing—ideal for home game rooms, arcades, cinemas, and parties
- Easy Maintenance: Comes with four keys for convenient access to coins and internal parts. This claw machine ensures reliable operation and long-lasting fun for home or business use
Commission the machine in stages
- Mechanical-only inspection: Move the gantry by hand. Check all four corners and the full travel for binding, racking, belt misalignment and cable snags. Confirm that the claw hangs vertically and can reach the chute.
- Single-axis motor tests: Run each axis slowly, verify direction and test both travel limits. Watch for stalls, missed steps and wiring that could be crushed or caught.
- Claw tests: Lower without a prize, confirm the lowest safe position, test closing with light objects and lift the heaviest intended prize. Check release over the chute.
- Complete-cycle tests: Run the full sequence with empty grabs, awkwardly placed prizes and prizes near walls. Test controls held against stops and confirm faults lead to a safe state.
- Repeated-play checks: Run many cycles and recheck fasteners, alignment, cable tracking, motor temperature and power connections.
Common failure modes and practical responses
| Symptom | Likely cause | Response and prevention |
|---|---|---|
| Gantry binds or carriage skews | Guides are not parallel, the cabinet is out of square, or bearing preload is too high. | Stop powered motion, inspect alignment through the full travel, then correct the frame or guide spacing before retesting. |
| Motor stalls or loses position | Moving mass is too high, acceleration is excessive, belt tension is too high, or motor torque is inadequate. | Reduce load and speed, inspect the drive path, and verify motor and driver requirements rather than increasing current blindly. |
| Lift cable wanders or jams | Poor spool flanges, inconsistent winding or a missing guide pulley. | Stop the lift, unwind safely and correct the spool or guide before another loaded cycle. |
| Claw swings or misses | Long suspension, abrupt acceleration or an off-center attachment. | Check centering and motion profiles; confirm the claw can settle before lowering. |
| Prize snags or will not release | Claw geometry does not suit the prize, the playfield is crowded, or the chute is obstructed. | Test a narrower range of prize sizes and inspect the claw and chute path. |
| Logic resets or inputs behave erratically | Motor noise, shared or undersized power, loose connectors or poorly wired switches. | Separate and verify power distribution, secure connectors and test switch behavior while motors run. |
| Travel ends in a collision | A missing, failed or incorrectly positioned limit switch, or reliance on software limits alone. | Disable the machine until physical travel stops and limit inputs are checked at low speed. |
What is needed to reproduce the idea
The Hackaday feature is a project showcase, not a construction manual. It does not supply dimensioned drawings, wiring diagrams, firmware, motor specifications, belt lengths, bearing spacing, claw drawings, power-budget calculations or calibration values. The component page lists zero downloadable files and zero formal instructions. A builder can reproduce the design approach, but not the exact machine from those pages alone.
- Do you have rigid structural stock and a way to keep the cabinet square?
- Can you build guided travel that stays aligned across the whole playfield?
- Are motor and driver current, voltage and duty-cycle requirements known?
- Can you provide fused, enclosed power and a reliable emergency cutoff?
- Can you fabricate or source a claw and lift that handle the intended prizes predictably?
- Can you test repeated cycles and safely recover from jams or power loss?
- Is the machine for supervised learning and experimentation, or for public or paid operation?
Salvaged parts make the most sense when they are low-voltage, inspectable, replaceable and adequately rated. Prefer new or purpose-built parts for mains power, heavy moving loads, safety-critical supports, or components whose torque, current or duty cycle cannot be established. For a modern recreation, aluminum extrusion, timing belts, current stepper drivers, cable carriers and a dedicated enclosed supply can simplify alignment and maintenance; those are modernization options, not components verified in the 2015 build. Pololu lists A4988 driver carriers in its official A4988 category, but a driver board alone does not establish compatibility with an unknown salvaged motor.
When buying is the better choice
For education, customization and reuse, building around available parts is the point. For a venue or event that needs a ready-to-run cabinet, predictable service and commercial features, a complete machine may be more appropriate. As one commercial comparison—not a specification for Johnson’s build—Made for Arcade lists a machine measuring 85 × 185 × 85 cm, weighing 130 kg and accepting 110–240 V at 50 Hz. The vendor also describes coin or token operation and programmable settings on its full-size claw skill crane product page; these are the vendor’s listed specifications, not independently verified test results.
That commercial documentation also warns buyers to consider supervision, unplugging before maintenance, rope maintenance and local regulatory compliance. A homemade machine should not be assumed certified for public use. Paid or public operation can involve electrical, amusement, prize, accessibility, insurance and local licensing requirements; determine what applies before deployment.
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