Author Topic: Weight on wheels?  (Read 4302 times)

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Blue

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Weight on wheels?
« on: December 28, 2010, 12:18:03 PM »
We need to be able to measure our weight-on-wheels with a hard mounted solid axle.  Any ideas?  The downforce goes to the ends of the axle, so the only place to measure it is the wheel bearing housing. 

With suspension, we can measure the weight on wheels with a linear pot hooked to the travel or a rotational pot (cheaper) hooked to one of the arm pivots.  I thought about strain gages on the axle to frame mount, but the downforce loads bypass this.

Offline Peter Jack

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Re: Weight on wheels?
« Reply #1 on: December 28, 2010, 01:00:23 PM »
The end of the axle would become a little more complex, but you could mount the bearing in a floating block with linear bearings front and back. below the block would be a solid platform and above the block you could install a load cell similar to that used in a platform scale. They're available in many shapes, sizes and ratings.

There's something to get the ideas flowing. :-o :-o :-D

Pete

Offline maguromic

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Re: Weight on wheels?
« Reply #2 on: December 28, 2010, 05:39:35 PM »
Blue, Talk about a mind twister, this could be tough one to solve. If there is a single beam that mounts the axle (or bearing housing) on each side of the car you could strain gage that, and even there you would have to either pocket the beam and get the gage on a neutral bending axis for side loads or add more gages to cancel unwanted loads.

Funny thing is yesterday I was talking to my friend Steve who is working on a project addressing a similar issue on how to do load cells on a McPherson strut suspension on a ALMS car.  If any of the info on that project looks like it would be helpful I'll let you know.  Tony
“If you haven’t seen the future, you are not going fast enough”

Offline hotrod

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Re: Weight on wheels?
« Reply #3 on: December 28, 2010, 09:00:17 PM »
Quote
We need to be able to measure our weight-on-wheels with a hard mounted solid axle.  Any ideas?  The downforce goes to the ends of the axle, so the only place to measure it is the wheel bearing housing.


Ummmm not necessarily.

If you can measure the stress applied by the down force, and add it to the body weight at the solid axle mount you could compute the actual weight on the wheels.

This assumes the down force is applied by a strut (like from a wing) where you could put a strain gauge on the strut to measure its load. If the down force is applied through a large structure which would be difficult to instrument it would not be workable.

It also depends on the degree of precision you need, if you only need a relative value, you might look at an RF tire pressure sensor on the wheels and log how the tire pressure changes (temperature rise would make this complicated), but once the tire reaches a stable temp, the tire pressure should have a correlation to the applied load. If the vehicle is a solid metal wheel that of course is not useful.

Larry

Offline Interested Observer

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Re: Weight on wheels?
« Reply #4 on: December 28, 2010, 09:39:27 PM »
For what it’s worth and in no particular order:

1)  Laser ride height measurement of tire deflection.  However, salt surface may not be a good reflector and salt surface deflection under the tire would be an unknown contribution.

2)  FEA the bearing housing to see if there are good locations for strain gauge(s).

3)  Modify OEM tire pressure monitor (or build improved equivalent) to send wheel hub or disc mounted strain gauge information.

4)  Sensitive proximity sensor to measure camber change at wheel rim.

5)  Strain gauges on mid-section of axle shaft with rotating sender and fixed receiver.  Like torque sensor but gauges arranged for axle bending.

6)  Smaller OD wheel bearing mounted in a slim-line custom load cell bushing.

In any case, calibration is going to be a ticklish matter.

Offline jl222

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Re: Weight on wheels?
« Reply #5 on: December 29, 2010, 12:38:40 AM »
  If to much wheelspin add wing or flap if no wheelspin decrease :-D

    JL222 :cheers: