Monday, August 7, 2017

Go-Kart plumbing

Plumbing is hard. That's probably why plumbers get paid more than some engineers, and why Mario can jump so far. Sadly the go-kart has both watercooling and hydraulic brakes (plus lots of wires, which are pretty much plumbing for electrons), so there was a lot more plumbing involved than I cared to deal with...

The loop is built out of PC-style cooling components. Cold water exits the radiator, flows through the inverter block and then through the motors before returning to the reservoir and pump.

The reservoir is a Swiftech MCRES Micro Its main purpose is to facilitate filling by acting as a source of water when the bubbles are pumped out. It doesn't actually store water for operation (evaporation rates are low), but without it, filling the loop is pretty much impossible.

The pump is a Swiftech MCP350-style unit pulled from a watercooled PowerMac G5. We were able to coax this one into turning on by pulling three of the wires (the rightmost three in the picture above) to +12V and one to ground, but I think the G5 pinout has varied over the years.

The radiator is a standard-thickness 240mm one, pulled from some unknown piece of lab equipment (but also easily purchasable from your favorite computer vendor). We were having trouble with the screw mounts shaking loose on the road (the radiator doesn't have real holes in it, just sheet metal). We replaced them with zip-ties, which have worked great since.

The fans are Dell Precision T5400 hard drive fans. They are much higher flow than a standard 120mm fan, but not loud enough to be annoying. Cheap too, under $10 a piece shipped from various eBay vendors.

The radiator is mounted between the driver's legs (under the steering wheel) with the fans pulling air through it and exhausting towards the rear of the kart. This allows the motion of the kart to provide some cooling assistance. We had a choice of mounting the radiator, inverter, or battery there, and the radiator was by far the safest.

The waterblock was made from a 8x12x1/2" piece of aluminum on a manual milling machine. No design went into the channel; the O-ring groove depth was selected using this chart, and groove width was done with the nearest available end mill, which worked out pretty well (the O-ring is quite squishy, so the widths don't need to be exact).

The block was fitted with G-1/4" rotatable computer fittings. These seem to hold up to loop pressure alright, though screwing the BSPP thread into the NPT tapered thread proved quite the challenge (but doable). The rotary fittings made routing the tubing much easier.

The thicker tubing is PrimoChill PrimoFlex. This stuff is expensive, but boy oh boy, it's worth it - super supple and able to make sharp bends without kinking. With a little bit of heat-gunning it also stretches nicely over the HSG fittings.

Overall it is remarkable how much heat the little Swiftech pump and 240mm radiator can move. Or not - a single 240 is easily good for a 300W GPU and 150W CPU under continuous duty with dinky little low-noise fans; the Dell blowers and natural go-kart airflow should be good for a solid 1KW+, and while the peak dissipation of the go-kart is high (each motor, stalled, is 3KW), the average dissipation on short courses is low.

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