RD-M1: Wheel encoder offset

This step-by-step guide is about measuring the wheel encoder offset for the RD-M1.

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RD-M1: Wheel encoder offset

Vehicle profile

The collection vehicle profile contains the three offset measurements from the RD-M1 reference point to the center of rotation of the wheel where the encoder is installed. The position of the wheel encoder must be measured and entered in the vehicle profile to compensate for the relative speed difference of the wheel and the RD-M1 when the vehicle turns. The circumference of the wheel is measured as the wheel encoder is calibrated at the beginning of a collection run.

What you will need

  • Hand level
  • Plumb bob or similar tool
  • Measuring tape
  • Marker or piece of chalk
  • A paved, level surface that you can make some marks on to park the collection vehicle
  • Vehicle Profile Measurements worksheet (at end of this article) or other paper to record the measurements
  • Writing utensil

Measuring the wheel encoder’s position

  1. Park the collection vehicle on a paved, level surface that you can make some marks on.
  2. Place one end of the level on the RD-M1 reference point.
  3. Center the bubble, and hold the plumb bob so the string brushes up against the RD-M1.
  4. Measure from the reference point along the bottom of the level to the plumb bob string, and record it as measurement 1.
  5. Mark the location of the plumb bob on the pavement.
  6. Measure from the bottom of the level down to the first mark, and record it as measurement 2.
  1. Mark the center of the rear wheel on the outside of each tire where it contacts the pavement.
  2. On the side with the wheel encoder, measure down from the center of rotation to the pavement, and record it as measurement 3.
  1. Move the vehicle forward so you can access all three marks on the pavement.
  2. Measure between the two marks made at the outside of each tire, and record it as measurement 4.
  3. Measure from the first mark perpendicular to the line between the other two marks, and record it as measurement 5.

Use the equations shown to calculate the three wheel encoder offset values

All the offset values should be positive. Do not enter a negative value for the L or R offset if the wheel encoder is on the left side of the vehicle. Which side the wheel encoder is on and the tire circumference will be calculated at the beginning of each collection run.

Create a new profile

  1. Open RD-M1 Collect. 
    • Until a profile has been created, the RD-M1 Settings screen will always open when the software is started. If this is the case, click Cancel to get to the main menu screen.
    1. Go to File > Preferences.
    1. Select the units for RD-M1 Collect:
      • For US English measurements, select SAE (the default setting).
      • For meters, select Metric.
    2. Click Save.
    1. Go back to File > Settings.
    2. Make sure New Profile is selected from the Profile drop-down menu.
    1. Enter a name for your new profile.
      • After a profile name is entered, the rest of the fields and buttons will become active.
    2. Enter the three offset values for the wheel encoder as previously calculated:
      • Up
      • L or R
      • Front
    3. Uncheck Display when program starts if you don't want to see the settings window every time RD-M1 Collect is launched.
    4. Click Save.

    Exporting and importing profiles

    Multiple profiles can be stored at a time, allowing for selection from a fleet of vehicles.

    Profiles can be transferred by exporting them to a file and importing the file on another computer. Importing a profiles file will replace all existing profiles with those from the imported file. You may wish to export the current profiles, if there are any, before importing a new file.