Spektrum SPMA9569 Sensor reading half RPM

[Elijah Brown]

Hi all, I switched to the Spektrum SPMA9569 backplate sensor after the last rebuild since the Futaba sensor is kind of a pain to get in just the right spot on my Trex 600. I did the resistor mod to pull the signal wire up to the power wire and get 97% reading. When the crank pin is under the sensor, it goes down to like 2% so I think the sensor is working.

When I run the engine however, it seems like the RPM reading is about half what it should be. A nice low idle is showing around 1100 RPM - YS56, no way it's actually that low so I think it's off by a factor of 2 somehow. The "Pole" count is set to the default (2) and can't go any lower. The settings are all the same as they were with the Futaba sensor. Has anyone else seen this before?

[Elijah Brown]

...anyone? I know others are using this sensor...

[Thorvald]

You should be able to set the divider to something other than 2 in your radio. In OpenTx, we simply set Blades to 1. No idea on Futaba as I've never used one but I can't see such a popular brand not having the ability to fix that.

Poles is for electric motors so maybe you have to tell the radio you are using nitro/gas/fuel and then the proper option will appear.

I just checked the 14sg manual and if you set the rpm sensor to magnetic you get the gear ratio option. Set ratio to 1.0 and voila, true engine rpm. Set ratio to your heli gear setup and then you will have head speed.

I set to optical you get the blades setting and likely it doesn't allow "1" to be picked. Try Magnetic.

Cheers
Tim

[Elijah Brown]

I have not been able to find any setting for the sensor type in the Futaba gyro. I think I will just reduce the gear ratio by a factor of 2 and hopefully that'll accomplish the same thing.