When assembling a robot, all the board should be attached to some kind of a board or frame. Later it may be needed to exchange a board or to add some new. When every board has its own pattern of fixing holes, the task will be hard. The frame is often not easily accessible and a partial robot's disassembly may be necessary.
To address the problem, all the bigger MRMS components use a common board form, with the following rules.
- All the fixing holes are 2 mm in diameter.
- Width is 35 mm. Very rarely a bigger width is needed. In this case it will be 70 mm.
- Length is a multiplier of 5 mm.
- There are at least 3 holes and very often 4, in the corners. Distance between their centers and board's edges are 2.5 mm.
- When a board is too small, the distances between holes' centres are multipliers of 5 mm, is possible. If not, multipliers of 1 mm.
Another problem are inter-board connections. This is especially prominent in controller - motor wires but other boards face similar problems. For example, motors offer different and not standardized solder contacts and that forces controller producers to offer either no terminal connectors of bare wire connectors with bolts, the solution which is awkward.
A part of this problem are different interfaces. As some chips offer I2C, some SPI, UART, or some multiwire parallel interface, it is very difficult to make a common wire to fit all of them. If You want to have a parallel interface with many wires, that will mean that every board should have a quite big connector, disabling miniaturization.
Therefore, MRMS offers some standardized solutions.
- To address problem with multiple boards' interfaces, CAN Bus alternative is offered for all the more complex boards, like ones with I2C, UART, or similar interfaces. They all need quite small common connectors with just 4 wires.
- CAN Bus connectors have 5 V power supply for low-current devices, so no additional cables are needed for small boards.
- If more current is demanded, thicker wires are needed, so 2 standard sets of connectors are used: Molex KK254 and Molex KK396. These 2 connectors are fairly common. Molex KK254 uses the same pins and Dupont 0.1", enabling You to connect Dupont connectors to Molex KK254. In a very rare case that the boards are too small for Molex connectors, Dupont 0.1" are used.
- BDC motors are connected with with Molex KK254 and Molex KK396 connectors, too, with adapters soldered to motors. BLDC motors need more wires so JST connectors are used.
- No other special connectors are used.
- All the manufacturers' codes of connectors are exhibited for do-it-yourself cables. Connector kits tailored to boards are provided.