AgOpenGPS v4 can leave the displayed wheel angle several degrees from zero when the required correction exceeds the Wheel angle sensor zero slider range of -127 to 127. Correct the sensor mechanically when possible; otherwise adjust the firmware's existing WAS zero baseline, upload the sketch, and resend the steering settings.
Understand the zeroing mechanism
The effective wheel-angle zero combines a baseline defined in the Arduino sketch with the zero offset sent by AgOpenGPS. The module applies a new baseline only when it receives new steering settings. Uploading a modified sketch without subsequently moving or resending the zero setting can therefore appear to have no effect.
| Item | Evidence-supported behavior |
|---|---|
| Zero slider | Provides a correction range of -127 to 127. |
| Firmware baseline | The sketch contains an existing WAS_ZERO value that establishes the center of the adjustable range. |
| Settings update | The combined zero is recalculated when AgOpenGPS sends new steering settings. |
| Integral Gain workaround | A proposed modification reuses the Integral Gain byte to extend the range. The evidence does not establish that this field will remain unused, so treat that change as custom firmware rather than standard v4 behavior. |
Choose mechanical centering or a firmware correction
With the wheels pointing straight ahead, first determine whether the sensor can be repositioned near 2.5 V while retaining useful travel in both steering directions. Mechanical centering improves use of the available sensor range. Do not force this arrangement if the linkage would pull the sensor beyond its safe motion or damage it at full lock.
Use a firmware baseline correction when an OEM sensor, linkage geometry, or restricted mounting position prevents electrical centering. Ackerman adjustment addresses unequal indicated steering angles; it is not a substitute for establishing the straight-ahead zero.
Calculate the required baseline correction
Two calculation paths appear in the evidence. Use only the path matching the measurement available on the machine.
| Available measurement | Decision or calculation |
|---|---|
| Displayed angle with counts per degree set to 10 | Required slider-count correction = -10 × displayed angle in degrees. A reading of 12.70° requires -127, which fits the slider. A reading of -23.56° requires approximately +235, so the firmware baseline must absorb the amount outside the slider range. |
| Sensor voltage with wheels straight | The documented sketch calculation uses 1288 counts per volt. One stated form is WAS_ZERO = measured voltage × 1288 - 127. |
| Difference from 2.5 V | The sketch comments also show difference = 2.5 V - measured voltage, count correction = difference × 1288, then WAS_ZERO = 3320 - count correction - 127. At 2.2 V, the documented calculation gives 0.3 V and approximately 386 counts, producing 2706. |
The two voltage expressions use different reference descriptions. Follow the formula documented in the specific sketch being uploaded rather than silently mixing the methods.
Apply the correction
- Point the wheels as straight ahead as practical. Set counts per degree to 10 if using the displayed-angle method, or measure the WAS voltage at the PCB between WAS high and ground or low if using the voltage method.
- Try the Wheel angle sensor zero slider. If the calculated correction lies within -127 to 127, apply it and send the steering settings to the module.
- If the required correction exceeds that range and mechanical repositioning is unsuitable, locate the existing
WAS_ZEROdefinition near the top of the autosteer sketch. Calculate its replacement using the comments and scaling in that same sketch. - Upload the modified sketch to the Arduino.
- Move the zero slider away from its current value and back, or otherwise send the steering settings again. This step causes the uploaded baseline and the AgOpenGPS offset to be read together.
Verify zero and steering-angle scale
With the wheels straight, confirm that AgOpenGPS reports approximately zero degrees. Then hold the steering at a known hard lock and adjust counts per degree until the displayed angle matches the machine's actual lock angle; the cited setup used about 35° only as the machine-specific target. Check both directions. If left and right angles differ, evaluate the linkage travel and Ackerman setting after the straight-ahead zero is correct.
If a sketch change appears ineffective, verify that the modified sketch was uploaded and that steering settings were resent afterward. If the slider still saturates, repeat the straight-ahead measurement and calculation instead of extending the range by guessing.
FAQ
Why does changing WAS_ZERO in the Arduino sketch have no effect?
AgOpenGPS must send new steering settings before the module combines the uploaded baseline with the slider offset. After uploading, move the zero slider and return it to the intended value so the settings are transmitted again.
How far can the AgOpenGPS v4 wheel angle zero slider adjust?
The documented Wheel angle sensor zero slider spans -127 to 127. If the calculated correction exceeds that range, reposition the sensor or change the sketch's existing WAS zero baseline.
Should I use Ackerman adjustment to center the wheel angle sensor?
No. Establish the straight-ahead WAS zero first. Use the Ackerman setting afterward to address unequal left and right steering-angle indications.
