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Old 07-06-2016, 08:08 AM   #1
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Default Ive got another question for EEs

(or anyone with more knowledge than I, really )

I run telemetry on all of my helis. I've gotten in the habit of splicing into the signal wire for my rpm sensor for the governor, and sharing the signal with the telemetry unit. This way I can use one sensor for two devices.

My question is should I also be splicing into the ground also? I've noticed some anomalies in the rpm being reported by the telemetry, (the reported rpms jumps all over the place) and odd behavior from the governor as well. I read something recently that made me think I needed the ground tapped as well.

In summery: I have my rpm sensor connected to my FBL unit for governor control. I have spliced into the signal wire only, and feed that splice into the rpm port on my TM1000 telemetry unit. Do I need to also splice into the ground and then feed that to the rpm port of the TM1000 as well?

Here is a pic for reference. You can see the single line going into the rpm port of the telemetry unit:

Thanks in advance!
Whiplash Gasser l Goblin Gasser
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Old 07-07-2016, 12:08 AM   #2
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I don’t think you mention- but what happens if you unplug the telemetry-side plug from the sensor? Does the governor work properly then?

Phase sensors are often used for RPM- and can have trouble depending on their type and the motor RPM/power. You may be chasing a problem that is not related to the telemetry connection.

On some level, you probably have the telemetry unit and the FBL sharing a common ground (unless they run independent power supplies with no shared ground). Doesn’t mean they have the same ground level- but chances are that if the problem exists only when both telemetry and FBL are connected, it is because the signal from the sensor cannot drive both in parallel in a way that the devices would see if they were connected separately.
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Old 07-10-2016, 09:36 AM   #3
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I agree with extrapilot, don't think the ground is your problem as it's common to both.

Unplug one of them and if it's resolved, could it be phase distortion ?

Just my 2 cents.
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Old 08-03-2016, 04:09 PM   #4
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The signature implies you are using a magnetic pickup on one or two gasser helicopters (Whiplash Gasser l Goblin Gasser)

I assume you are using the Spektrum TM1000?

On my Trex 600N with the Spektrum TM1000 and the MSH Brain, I use one Align magnetic pickup that is split between the two devices.
The sensor is powered by the Brain (white / red / black) and I split the white wire that leads to the TM1000 (white only)
The TM1000 gets its power from the Brain's servo power rail via a Y-cable on one if the cyclic servos.

On my Trex 700 with the Spektrum TM1000 and MSH Brain, I mounted two Align magnetic pickups.
Each pickup is powered by the device it is connected to (TM1000 use 3 wires to sensor #1 and the Brain uses 3 wires to sensor #2).
The TM1000 is connected to the Brain's servo power rail with a Y-cable to one of the swash servos.

Both helis use a 3S LiPo and a Scott Grey Reactor HVX set to 8v output
The Brain's gov sensor is regulated to 3.3v output and I think the TM1000 is also regulated to 3.3v.

On both setups, the TM1000 is almost completely useless.
At the end of the flights, it will have reported anything between 0 and 50,000 RPM.

The 600 uses two magnets on the flywheel (max RPM should be 16,000) and the divisor in the TM1000 is set to the same as the divisor in the Brain.
However, the Brain's gov is locked in and never complains

The 700 uses the clutchbell. The same divisor is used in the TM1000 and the Brain. Again, the Brain never complains.

I have tried adding a black lead on the 600.
But obviously, the black lead is present on the 700.
And, it makes no difference.
The TM1000 causes more trouble than it is worth.
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