Eagle Tree Car Data Recorder User Manual

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http://www.eagletreesystems.com

Page 3

typical Car 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 Recorder kit includes four magnets, providing you with up to three spares.

Figure 2: RPM Sensor & Magnet

Installing Magnets

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. If you decide to use only
one magnet, make sure you double the gear ratio to “2” on the Calibrate Motor RPM page under the Tools menu in the app.

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 engine 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 engine already has magnets mounted for some other purpose, there’s a good chance you can use them. Take one of the
magnets included with your recorder, and put that magnet up against the previously mounted magnet. If the red line of the Recorder
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), though we have
not tried it.

We are often asked whether existing magnets on spark ignition engines can be used. The answer is “yes” in most cases, if you can
install the sensor near enough to rotating magnets. We have found that these engines typically have 3 magnets, with 2 magnets
mounted with one polarity, and the other one with another polarity. The easiest way to use these magnets is to install the sensor with
the printed side facing the magnets (as described below) then run the motor and see what RPMs are recorded after setting up the gear
ratio. If the RPM looks like it is only half of the correct value, double the gear ratio value you entered, to compensate for only one
magnet being in the right polarity. We have received problem reports of RPM reading errors when the RPM sensor is mounted very
near the magneto of spark engines, so we recommend mounting it 180 degrees away from the magneto, or as far away as possible.

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 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 propeller to ensure complete freedom of
movement. Also make sure that the sensor won’t vibrate and come in contact with the magnets during driving. If this happens, the
sensor will be destroyed, and the Recorder could be damaged.

Once these steps are complete, plug the Futaba style connector on the sensor into the recorder as shown in figure 1. Note that a
standard Futaba style servo extension cable can be used to lengthen the wire if needed.

Using Existing RPM Sensors