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Archive for April 7th, 2013

Makergear M2: Heated Build Platform Cable

The power + thermistor cable for the M2 Heated Build Platform attaches to the Z axis stage at the Y axis motor, with the conductors encased in a fairly stiff braided loom. The cable flexes from fully retracted to fully extended as the HBP moves along the Y axis. Here’s a view at about mid-travel:

M2 HBP cables - wire loom

M2 HBP cables – wire loom

Unfortunately, there’s no provision for strain relief at the HBP or around the connectors. The silicone heating pad firmly anchors the two pairs of power wires to the aluminum plate, but that simply means they flex sharply at the edge of the pad:

M2 HBP connections

M2 HBP connections

I removed the loom between the motor mount and the connectors, but that still doesn’t provide nearly enough flexibility:

M2 HBP cables - loom removed

M2 HBP cables – loom removed

The wires still flex sharply at the outboard side of the connector and at the HBP pad; this can’t possibly survive more than a few thousand long cycles before something expensive breaks. The Thing-O-Matic HBP connector debacle suggests that I may need to attach a strut to the Y axis stage that rigidly supports the connectors, with a much longer loop of wire soaking up the strain to the fixed end.

The 18 AWG wires carrying the 10+ A of HBP current get unpleasantly warm, suggesting that new loop will require heavier wire. In round numbers from that table, 18 AWG stranded wire runs 6.5 mΩ/ft, so the (roughly) four feet of wire pair between the electronics case and the HBP will drop 250+ mV and dissipate 2.5 W. I suspect it’s worse than that, but haven’t made any measurements to back up that suspicion.

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