G sensor placement?

[dannyho]

I had some free time at work today and I started some calculations as to lateral acceleration. And I worked out the change in it as you move in towards the center of the circle (skidpad), I did this for a 100' pad (50' radius)and this becomes more pronouced for tighter radii.
I've searched for g-tech mounting and Measuring G force, but I didnt turn up anything so I'm making this post. Maybe I'm missing something, but i read through the g-tech manual and it doesnt meantion where it should be placed, even though the center of the car seems to be obvious. I'm really not trying to start anything, but congruency is important in all measurments otherwise you can't compare them. I remember a post about slalom speeds that showed this exactly.

Just to illustrate my point here is what the g forces would look like inside the car for a turn radius of 50 and 25 feet, under the outside tire, with 1g being the baseline at the outside tire.

50 ft radius
outside tire -------center of car ----------inside tire
1g ------------------ 0.95g---------------- 0.9g

25 ft radius

1g --------------------0.90g ----------------0.80g

This means if I go about getting the Autometer D-pic, I'll have to be careful on where I put it.
What are your thoughts? I've seen kids quote G readings some withit up to the left on top of the dash and some with it in the center. Has a standard been "set" or should we do it right now

[Steve1968LS2]

I would think the lateral-g's would be the same anywhere in the car.. It's like a car going 50mph.. the whole car is going 50mph.. lol -- It migh matter a little but I doubt two feet in any one direction would make that much of a difference. For instance the car is doing a 100ft skidpad clockwise. A sensor on the left side of the car would be doing 100ft, the center of the car would be doing 98ft and the right side would be doing 96ft. As I said though.. I'm not even sure it would matter since I would think the whole car (assuming no loss of traction) would be doing the same g's..

My track computer just says it needs to be mounted LEVEL. I would mount it near the center of the car though.. Mine is just ahead of my shifter on my trans tunnel.

[dannyho]

that would make sense if it was proportional to the speed of the car but it's not. lateral acceleration is proportional to the square of the speed. ie a=(v^2)/r and acceleration is not constant along a line of motion. take a space station that revolves around an avis to produce an effective gravity. the gravity will be less at the center of the circle than the outer rim.. this is simple physics, not even physics 101, this is high school stuff.

[baz67]

Put it as close to the center of the car as possible. That way the amount of error is as close to the same in both directions.

[sinned]

Almost every new car built today has a "G" sensor located in the vehicle for one thing or another, some have multiples including yaw and steering input for desired turning radius. Without exception they are all mounted as low as possible and in the center, usually under the center console or under the seats in the case of bench seating.

[chicane67]

You should find the placement of the CG, forward/aft, and then mount it on that centerline of left/right. Mind you, that it will most likely not be on the centerline of the chassis itself. This will put the sensor within its "window" of operation and will provide results close enough to call it good.

Since the CG moves around during driving, placing the sensor within this "window" will net you the results that you are looking for and the measurement will be repeatable.

If it is not placed at the bottom of the CG lever arm, there will be a small amount of error. This error however, is calculable and can be entered as a simple offset. It really isnt all that necessary due to the fact that the CG is going to be moving around... but in the end, if you put in an error offset of a given percent for the movement, you can pretty much assure yourself of a measurement within 1 - 2%.

[trackrat79]

How does the cg change during driving. The cg of a vehicle is pretty much a constant except for fuel burn off I thaught.

[sinned]

The weight of the vehicle in motion is dynamic, for/aft and side to side motion changes will cause the CoG to move as weight is transferred around the static CoG.

[Scott Parkhurst]

Isn't this obvious?

It goes on the G-spot.

duh!!

~SP~

[baz67]

Isn't this obvious?

It goes on the G-spot.

duh!!

~SP~

I guess he has not found that yet.

[Steve1968LS2]

that would make sense if it was proportional to the speed of the car but it's not. lateral acceleration is proportional to the square of the speed. ie a=(v^2)/r and acceleration is not constant along a line of motion. take a space station that revolves around an avis to produce an effective gravity. the gravity will be less at the center of the circle than the outer rim.. this is simple physics, not even physics 101, this is high school stuff.

A space station is slightly larger than a car.. lol.. I just meant that a couple feet in any one direction shouldn't throw off the readings much. The most important thing (in my case) is to mount it level. The trans-tunnel seems to be the most logical palce to mount it.

[chicane67]

Isn't this obvious?

It goes on the G-spot.

duh!!

~SP~

Yo Scott....
Not to get off subject.... but when might we see the "Nevada Adventure" in writing ?? I heard there was another 'issue' during the event that pretty much stopped the show ??

[dannyho]

right, I was just using the space station thing to illustrate a point, but even in that, the acceleration is only related to the distance from the center and rate or rotation, and not the mass of the station at all.