Measuring RPM with the eLogger, Using the Hall RPM Sensor with Magnets
Installing the optional Hall RPM sensor and magnets is the most challenging part of installation, but is relatively easy once a good
mounting location is determined.
To install our magnets, first find a suitable location on your motor or drivetrain to attach either one or two small magnets and RPM
sensor. Typically, the prop washer or prop hub are ideal locations for planes, and the car’s axle shaft is good for car installation.
This will of course vary with the construction of the model. Make sure the magnets are mounted on some structure that doesn’t “flop
around,” as the magnets could hit the sensor in this case. The RPM sensor must be mounted so that it does not move around, and is
within 1-2 mm of the two magnets as they spin. On typical plane installations, there’s usually a place where the back of the sensor
can be glued to a flat surface under or over the hub which has the magnets mounted. The RPM sensor kit includes four magnets.
That provides you with up to 3 spares.
Once you have determined where to install the magnets, decide whether you will drill a hole so that the magnets will mount flush with
the surface, or if you will just glue the magnets to the surface. Though somewhat more difficult and permanent, mounting the
magnet flush with the surface is the best long term approach, since the mounting will be much more rugged, and the risk of imbalance
due to not mounting the magnets exactly 180 degrees apart is reduced. In fact, if the magnet is mounted flush in another metal
material, it is quite possible that no shaft imbalance will occur if you only mount one of the magnets total.
To flush mount the magnets, drill a hole just slightly larger than the diameter of the magnet size you choose, and of the same depth as
that magnet. If you decide to surface mount the magnets, thoroughly clean this area and lightly scuff it to improve adhesion. Glue
the magnets with the side marked with a red line facing inward (hidden), using epoxy, or other strong, suitable glue. It’s important
that the red line on the magnets faces away from the sensor once the sensor is installed. The magnets should be glued 180 degrees
apart to keep the shaft in balance.
WARNING: make sure that the magnets are glued sufficiently so that they will not detach and create a
hazard, and always wear safety glasses when your motor is running! It is also a good idea to put a piece
of heatshrink tubing or electrical tape around the magnets, to further secure them.
Using Existing Magnets
Note: if your motor already has magnets mounted for some other purpose, there’s a good chance you can use them. Take one of the
magnets included with the RPM sensor kit, and put that magnet up against the previously mounted magnet. If the red line of the
eLogger magnet faces down so that the sensor can be mounted facing the side of the magnet with no red line, mount the sensor with
the printed side toward the magnet. If the side of the magnet with the red line is visible when on top of the previous magnet, the
polarity is reversed. This should work correctly if you install our sensor backwards (printed side of sensor away from magnets).
Installing the RPM Sensor
Once the magnets are glued and completely dry, temporarily position the RPM sensor so that the side of the sensor with printing (or
a colored dot) is facing the side of the magnets WITHOUT the red line. The sensor now needs to be glued so that it is held
rigidly into position. Before gluing, put a small spacer (1-2 mm thick) between the sensor and one of the magnets to ensure proper
spacing. If desired, a small piece of brass tubing can be glued or heatshrunk to the back of the sensor to ease mounting and increase stability.
After the sensor is glued and completely dry, remove the small spacer and rotate the drive train or propeller to ensure complete
freedom of movement. Also make sure that the sensor won’t vibrate and come in contact with the magnets during operation. If this
happens, the sensor will be destroyed, and the eLogger could be damaged.
Once these steps are complete, plug the Futaba style connector on the sensor into the eLogger as shown in figure 1. Note that a
standard Futaba style servo extension cable can be used to lengthen the RPM sensor wire if needed.
Using Existing RPM Sensors
Several of our customers have been able to use existing RPM sensors, such as governors or turbine sensors, with our products. The
following steps must be followed:
1) Determine the “pinout” of the existing sensor. Compatible sensors will have Power, Ground, and Signal connections. The
eLogger’s RPM pinout, from left to right, is: Power (black wire), Ground (red wire), Signal (white wire).
2) Devise a “Y” cable to connect your existing sensor to it’\s connection, and also to the eLogger’s RPM connection. NOTE:
Power for the sensor should come only from the connection the sensor is normally plugged into. So, only Gound and Signal
wires should be routed from the existing sensor to the eLogger. The power wire of the Y cable between the sensor and the
eLogger should be cut before connecting it to the eLogger. This is necessary to avoid connecting the power of the existing
sensor connection to the eLogger’s power connection.
3) Thoroughly test the system to make sure the sensor still works with whatever it was originally connected to, after Y’ing to the
Installing a Secondary RPM Sensor
A second MODIFIED Brushless RPM sensor can be plugged into the eLogger’s THROTTLE input, for measuring RPM of multiple
NOTE: the Optical and Hall Effects RPM sensors CANNOT be used as secondary sensors, and will be damaged if plugged into any
port other than the RPM port. Only the brushless RPM sensor can be used for secondary RPM.
To measure secondary RPM, the RPM sensor must be modified as follows:
· Carefully pry back the plastic tabs that hold the RED and BLACK pins in the RPM sensor connector, and remove the red and
· Replace the red pin where the black pin was, so that the pin order in the connector is RED, OPEN, WHITE.
· The second RPM sensor plugs into the throttle port with the red wire toward the label side of the logger.
· The black pin (left detached from the connector above) connects to the upper “Tmp 3” pin, nearest the label.
NOTE: The second RPM channel is automatically set up with the same sensor type and gear ratio as the primary RPM. So, it’s
important that the same type of sensor be used for primary and secondary RPM.
The secondary RPM sensor(s) are logged and displayed on the screens with the other parameters, as described below.