Spectrum Electric RPM Sensor
 

After giving up on getting two electric motor/speed control sensors to work properly on two different motors and speed controls, I decided to take the advice of others and convert to the SPM1452 optical sensor.

After reading some of the various entires concerning the subject, I also looked for a plug & play way to connect the optical sensor to the TM1000 Telemetry unit.

When all was said and done, the Spectrum SPMAJST3, 6" Quick disconnect Remote Rx Ext solves the problem. Even the wire colors match!

It has the white female connectors on each end, and a servo type male & female in the middle. You use 1/2 of the extender as plug & play, then changing a female servo connector from female to male to use the other half on a second sensor if needed. (I go by pins, not connector shells)

As first tested, the sensor will read either from the included stick on marks, or even using the E-Flite white logo on the black rotating part of an E-Flight Power 25 motor case. The sensor has two little black rectangular optical assemblies on one side. Motor rotation should be such that it rotates across the two sensors, from one to the other. The TM1000 has a red led that changes blink rate or intensity as the RPM reading changes.

Additional Info. The Optic sensor leads to the TM1000 can pick up "noise" from the speed control and/or the motor leads!
Evidently, the TM1000 senses the voltage "spikes", and adds them intermittently to the optical sensor output! Even so, the optical sensor seems to produce a more stable reading than the electric motor sensor did with the same motor and speed control.
(E-Flite Power 25 and E-Flite 60A speed control.



So, at this point, I have two extremes, the TM1000 sees everything, resulting in very high and intermittent readings, or very low, where the TM1000 sees what appears to be the basic switching load rate of the speed control. Next will be to see if added capacity or another ferrite core or two can eliminate the false signal that the TM1000 is seeing. It might be coming from the receiver power that is fed to the TM1000, or because the switching pulses involve several amps, be radiating from various leads.


May 3d
Got out my trusty crimper and cable kit, and made up an extension with a split ferrite cylinder, and three turns of cable through it. Did a quicky bench run with the Power 25 motor inside an Alpha 40 Trainer.
So far the RPM readings are stable. This leads me to believe that the cable connected between the TM1000 and the optical sensor output cable is picking up noise from the speed control/ motor, and the TM1000 counts the noise spikes. More extensive tests with an external Tach tomorrow or so. The weather tomorrow might be the last really good weather for a few days.

May 5 That was interesting!
Further testing with the ferrite core mentioned above and using a Power 25 Motor and 60A EFlite speed control with BEC.
The ferrite core is big enough that it filters out the pulses from the optical sensor, and the TM1000 sees a pulse train that approximates a 2500 RPM sensor reading,
(there is one silver "dot" on the black portion of the motor case, and the Motor RPM was checked with an external hand held optical tach.)

RE: Spectrum Electric RPM Sensor
 

I'm loving the 1452 sensor...  haven't seen any spurious spikes on any of the planes I'm currently flying.  I would like to see a picture of the wire harness you found.  It sure would be nice if they started including a deans convertor cable along with the 5 dollar sensor.  Just charge 10 bucks instead of 5.  It cost me more for the shipping than the sensor and the Optical sensors seem to be in abundance.

KKKKFL

RE: Spectrum Electric RPM Sensor
 

The cable you wanted to see a picture of is at
http://www.horizonhobby.com/products...nsion-SPMAJST3

RE: Spectrum Electric RPM Sensor
 

Ok,
But it looks like we are still paying 10 bucks to get that little white piece of plastic on the end.  Surely there's a less expensive way to get those connectors.  A Ten spot ought to buy a package of 4 with 3 inch pig tails.  I don't mind soldering.


KKKKFL

RE: Spectrum Electric RPM Sensor
 

Sure, Digikey will sell them to you...

With a $25 minimum order.

Andy

RE: Spectrum Electric RPM Sensor
 

Maybe I can pull together a group buy

KKKKFL

RE: Spectrum Electric RPM Sensor
 

Well, at some of the shows/flyins, you can buy pigtails for $1-$3 ea.
By changing one of the servo style connectors on the spectrum cable, you end up with two adapter cables for the $10,
neglecting the cost of the one additional servo style connector and pins.

RE: Spectrum Electric RPM Sensor
 

I found a hobby shop that carried a 1" cable (Dean/JST3) connector for just 4.99...  Shipping was more than the connector.

KKKKFL