An electronic STEM kit is a plastic programme with electronics inside it. The kit only works if the moulded parts hold a battery in contact with a spring, keep a motor shaft aligned with a gear and let a child snap two halves together without tools. Our work on these kits starts from the component list rather than a single product drawing, because the buyer is usually specifying a system of twenty to forty parts that all have to fit the same PCB family.
We supply the full moulded component set for circuit kits: battery cases with tool-required covers, motor and switch mounts, wire-routing clips, terminal blocks and the base plate the whole experiment builds on. Buyers who already have a kit design send us the PCB drawings; buyers starting from a concept get the component list drafted with the electronics engineer before tooling.
Battery cases
The battery compartment is the most safety-critical moulding in the kit. Covers are specified with a captive fastener — a screw with a captive washer or a moulded quarter-turn latch — so the cover cannot be left loose after a battery change. Contacts sit in moulded pockets that preload the spring, because a battery that rattles in its case produces the intermittent faults that generate returns. Where a kit ships with lithium cells, the case is quoted to the transport test standard the buyer nominates.
Snap fits that survive children
Snap-fit cantilevers are sized for the resin, not copied from a drawing: ABS takes a 5 percent strain at the hook root, PP about half that, so a PP clip needs a longer cantilever or a different geometry. We simulate the hook deflection before cutting steel, and the first-article report includes the insertion force measured on a push gauge. A kit that a seven-year-old cannot open is as much a failure as one that falls apart.
- Cantilever hooks sized per resin, insertion force verified on first articles
- Living hinges specified only in PP, with the gate placed away from the hinge line
- Brass inserts quoted where a screw joint will be opened repeatedly
- Colour coding by material so assembly staff cannot fit a wrong part
Motor mounts and alignment
A motor mount is an alignment part, not a bracket. The bore that holds the motor and the boss that carries the gear are moulded in the same shot so their alignment is set by the tool rather than by assembly. Where the kit runs a motor and a gearbox, we quote the mount and the gear housing as one tooling family with the gear cavity specified for backlash, because a mount that holds the motor perfectly but lets the gear mesh wander will whine after a week of classroom use.
Material selection
ABS carries most housings because it takes a screw boss cleanly and plates well. PP is used for living hinges and battery covers where fatigue matters more than stiffness. PC is specified only where a window or lens needs clarity, with the moulding conditions set to avoid the internal stress that turns a clear part cloudy after a year on a shelf. All resins are quoted with the flame-retardant and colour-masterbatch options the kit needs.
Specification
| Component set | Battery cases, motor mounts, clips, terminal blocks, base plates |
|---|---|
| Materials | ABS housings, PP hinges and covers, PC windows, POM gears |
| Tolerance | Plus or minus 0.05 mm on snap fits, plus or minus 0.1 mm general |
| Snap fit | Cantilever hooks sized per resin, insertion force reported |
| Battery cover | Captive screw or quarter-turn latch, tool-required opening |
| Colour | PANTONE matched, colour coded by material family |
| MOQ | 5,000 pieces per component, kitted sets quoted as a programme |
| Tooling | 25 to 40 days per component family |
Kitting and documentation
Kits ship as bags of parts with a printed instruction sheet, so the moulded components are counted, bagged and boxed to a bill of materials that we verify piece count against before sealing. Each component carries the kit revision number in the tool, so a revision change is visible on the part rather than inferred from paperwork.
For mechanical kits without electronics, see our STEM gear building kit programme, or browse all Educational & STEM Toys.
