View Single Post
  #3   Report Post  
Posted to sci.electronics.repair
Elder Jones Elder Jones is offline
external usenet poster
 
Posts: 3
Default Camber smartphone electronic measurement accuracy & precision

It seems that recently said:

I'm sure it depends on how accurately you park the vehicle on the phone. :-)


The three measurements that we need to accuracy & precision of about a
tenth of a degree are caster, camber, and toe.
o Caster is a function of camber at ±20 degree angles
o Camber has a range of from 0 to about ~±6° ~±10'
o Toe has a far smaller range of about 0.05° to about 0.1° per wheel
[https://blog.bavauto.com/11758/bmw-a...wear-diy-kit/]

Since toe can be more easily measured linearly, only tenths of a degree
accuracy & precision would be required for measuring Caster & for
calculating Camber.
[https://forums.bimmerforums.com/foru...eel-Alignment]

For toe, we can obtain linear equivalents simply by converting a factory
given front total toe spec of 0°5'±10' and a factory given rear total toe
of 0°22'±4' to a non-angular linear distance given just the tire diameter
a. P235/45R17 = (235)(2)(0.45)(1/25.4) + 17 or about 25.3"
b. Factory total front toe = 0°5'±10' & factory total rear toe = 0°22'±4'
c. Toe from tread centerline to vehicle centerline is half that
d. Individual toe to centerline is 1/2 of 0°5' = 0°2.5' (halving may not be needed though)
e. 0°2.5' divided by 60' is ~0.0417 decimal degrees
f. 17" diameter rims * tangent ~0.0417° = 0.0124"
g. 0.0124" is roughly about 3/256ths" (or about 0.3mm)
[https://www.bmwcca.org/forum/index.p...nt-specs.979/]

The rears, calculated similarly, would be ~0.33" for total toe in.
[https://robrobinette.com/ConvertToeDegreesToInches.htm]

We could also use the sine instead of the tangent if we consider the radius
of the tire to be the hypotenuse (the linear measurements are likely to be
taken at right angles to the centerline of the car, or an imaginary line
through the steering axis parallel to same) not at right angles to the tire
centerline; but at these tiny angles sine and tangent are basically the
same anyway so that makes no significant difference where the major linear
measurement error is likely in the gravitational bowing of the typical tape
measure. Hence the toe measurement accuracy & repeatability is due more to
the fact that the tire isn't very large, and the factory-specified angle is
very small, causing even a miniscule difference in distance with the tape
measure to translate to a fairly large portion of the angle.
[https://forums.pelicanparts.com/pors...ees-help.html]

Given that both toe and caster can be derived from other measurements, the
only question at hand is for Camber degrees to be measured by a smartphone.

For Camber, tenths of a degree in repeatability & accuracy would be nice.
Does anyone here know if a typical smartphone can achieve that feat yet?

If not...
When do you think phones will be able to achieve that accuracy & precision?