Fitting a governor sensor to the Trex 600n

Author: Rob Turnbull
Article Date: 13th April 2008

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The trex600n has an inverted fan so the magnet is above rather than below the fan. This means that instead of attaching a governor sensor bracket to the engine mount, you need to fit it either inside or outside the frames above the fan.

There are two holes in both sideframes in the correct position to fit the sensor bracket. Which side you fit the sensor to depends on which way around you made up the sensor bracket. I generally opt to mount the sensor on the right hand side of the helicopter being the side I use when mounting to the side of the engine, but when the sensor is fitted above the fan it doesn't matter which side you mount it to as the muffler isn't in the way.

If you haven't assembled the sensor yet, please see the article on how to build the governor sensor.

The first thing to do is to remove the engine and fan assembly from the heli. See the article for instruction on how to remove the engine, if needed.

If you need more room to work in, you can also remove the clutch stack leaving nothing in the way of fitting.

  • The sideframe mounting holes (vertical)The sideframe mounting holes (vertical)

The horizontal holes can be used to mount a sensor using just a tie-wrap without a bracket if preferred.

I choose to fit the mounting bolts from the inside of the frames so the nyloc nuts are on the outside to make it easy to grip them when tightening up. The other reason I do this is due to it being easier to fit a hex driver onto a bolt inside the frames than to grip a nut in there. Especially when altering the alignment when everything is installed.

Add a washer to an M3x8mm bolt and slot it through one of the holes from the inside of the frames, fit the sensor to the sideframes with the sensor head hooked underneath the frame and then fit a nyloc nut onto the bolt to hold it in place. Only gently tighten it up for now as you may need to move the sensor a little bit to make it sit over the magnet correctly.

Fit the second bolt and then gently tighten it up again to hold the sensor in place ready for adjustment with the fan in place.

  • Sensor loosely fitted and ready for alignmentSensor loosely fitted and ready for alignment

You will need to cut the fan shroud hole a little larger to allow the sensor to poke through where required.

To check you are going to cut the hole in the right place, remove the two halves of the fan shroud from the engine and fan assembly, push them back together and fit the fan shroud back into the helicopter.

  • Hole cut in the fan shroudHole cut in the fan shroud

Refit the engine to check sensor alignment. Just a couple of bolts are needed to hold it in place and squared up properly.

The magnet in the fan should pass directly below the sensor and you need about 1.5 to 2mm gap between the highest point of the fan/magnet and the underside of the sensor to avoid them colliding in use.

With the best sensor position found, tighten the bolts up to hold it firmly in place.

I find the sensor bracket aligns just fractionally off vertical (tilting the top edge to the right) to get the best alignment over the magnet.

If you removed the clutch stack for easier access, now is the time to refit it.

Now refit the engine and fan assembly with the fan shroud fitted and secure it to the helicopter.

  • Governor sensor fitted to the heliGovernor sensor fitted to the heli

The last thing to check is that, with everything fitted, the sensor does not catch the fan at all. If it was fitted and aligned correctly this shouldn't be a problem, but the sensor can move when tightening up, so do check it!

You can turn the fan around using a hex starter in the starter coupling.

You should also plug the sensor into the governor and switch on your helicopter in order to check the sensor is picking up the magnet. See your governor documentation for details of how to test the sensor.