Saturday, October 19, 2013

Nitron Technical Observations

This is probably a Part 1 since this is an ongoing project, but I am working occasionally but steadily on a 'Tron overhaul for an HvZ player at a nearby campus. Along the way I came across 2 odd details about the stock Nitron electrical system.

One is that the pusher is cycle-controlled (with the switch mounted on top of the battery box that follows the stepped edge of the cam disk) but there is no active braking. Weird. Except it makes sense in combination with the next bit, which makes AB difficult to implement in the stock configuration.

This strange heatsinked 4-pin package hanging off the side of the PCB is the first thing many people notice about the stock motor setup on the 'Tron pusher.

Speculation has included that the device is a voltage regulator or a MOSFET (used for solid-state switching of the motor power with the small switches scattered all over the Nitron's guts for various interlock purposes). At least people are aware you have to remove this PCB to do anything useful. As it turns out, "voltage regulator" is a very close guess.

A close inspection of the IC in question reveals the markings "UTC" and "AN6651". A quick Google nails it down what the mystery component is: a linear motor speed control IC. More or less a fancy linear voltage regulator that allows taking into account the motor IR and Kv in the selection of 2 external resistor values to get a very stable constant-speed, governor-like behavior.

Here is the datasheet:

Interesting. Peak current handling is 1.75A. Sounds awful low. Applications listed in the datasheet include tape decks and CD players. So why was this component used to drive the Nitron pusher motor? That is the biggest mystery of them all. Could there possibly be a need for that tight of speed control of this motor? Surely if the stock setup demanded a lower ROF than the direct-driven motor would produce and no colder-wound motor was available, you could do well enough with a dumb, cheap, string of diodes - or even a generic voltage regulator.

Could it have something to do with dropout voltage? Haven't checked, not worth the time to investigate the numbers of this application.

Regardless... the Nitron pusher motor is governed. This is why throwing higher voltage batteries at a stock 'tron makes the flywheel rev higher, but doesn't change the terrible ROF.

Here's a demonstration in which I throw various packs at the stock gearbox without any change in speed. First 7.2V, then 10.8V, then 12.0V.

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