If you mount the bno085 in your PCB box and have the box fixed to the cab floor does cab suspension have any affect on bank sides as the cab tilts over more than the tractor
Would the bno085 be better mounted on the back axle under the cab
If your antenna is 3 m from ground 1 degree of rotation will be ~5.2cm. So if your cab tilt 1 degree more than tractor you will have error of ~5cm.
If IMU is mounted on tractor reading 0 tilt and cab with antenna is 1 deg side ways it will drive ~5cm error.
IMU on tractor antenna on hood fixed to tractor eliminates cab suspensions error.
Or IMU and antenna in and on cab with IMU corecting for cab tilt. It shoud be better to leave IMU in cab. Better to mount IMU lower than higher.
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Isn’t it a bit more complicated than your example above. One would need to take into account the cabin suspension height, the point where the cabin tilts. Note that the antenna moves along the cabin. If the tilt point was at ground level, then the IMU would work perfectly when fixed to the cabin while an IMU fixed to the tractor chassis would make a big error.
I believe the chassis tilt height would typically be much lower than half the tractor height which would mean IMU fixed to the cabin would work more accurately than an IMU fixed to the chassis.
Would be interesting to have some measurements of the difference of the cabin tilt to the tractor axle tilt at different tilt angles. Must be dependent on the actual tractor model too.
If IMU is on cab it will compensate for cab and tractor tilt, error from cab suspension is measured from antenna to cab tilt plane. If tilt plane is half distance from ground error will be 1/2 if tractor is level but cab is at an angle.
Potential problem is AOG thinks that whole tractor is at 10deg tilt so it will compensate ~52cm for 10deg on 3m height of antenna, this will over compensate ~26cm to other side of line.
(Lower cab tilt plane is IMU will work better down to ground where error will be 0).
IMU on chassis will read 0 deg tilt and with antenna on cab with 10deg roll and 1.5m height to tilt plane error will be ~26cm.
No IMU error will be ~26cm.
Theoretically there is no difference in error in this example but in reality cabs will be on different heights, suspensions, there will be combination of tractor/chassis tilit with cab tilt and other factors.
On an average slope today I measured the cab shocker bolt centres and one side was 138mm and the other side was 148mm and the shockers are mounted 900mm apart
Obviously you would need more measurements to work it out exactly but roughly how much difference would it make with that amount of movement
a= 10mm
b=900mm
α = ?
tan(α) = a / b so α = arctan(a / b)
arctan (10/900) = 0.636 deg
Error will be ~0.6deg if from tilt plane (from middle of springs) to antenna you have 1.5m,
it will be ~1.65cm error.
Easier to install in cab and better for suspension cab.
What is better?
- Antena and IMU on cab
- Antena on the front and IMU on the chassis