I was playing around with calculating a proxy for weight transfer so that students can see tire load changing based on g-forces / inputs. The boxes around the g-force meter indicate/approximate relative load on tires.

7 Color codes Ranging from Blue (least load) to Red (most load).



Thoughts on how useful?

One big limitation is that there is no Z-axis acceleration measured by the vbox, so no elevation loading can be incorporated.

(Basically is a combined g-force vector projected onto a 45 degree plane).

 

Not having a Z load will definitely cause some error, but it will still probably be helpful for some students. If nothing else, it will give them a visualization of how the load varies in the tires based on their inputs. Neat calculation.

 

Very cool! I'd be interested in trying it out.

 

If you have a HD2, pm me. If you have a working 996.997.991 ref file, I can convert this scene to use those. This one is setup for a GT4 right now.

 

I have a working 991 ref file.

 

Ok, I think I have a 997, 991, and GT4 version working. Anyone with a non GT3 997/991, or GT4 PM me for a copy to try out.

 

Ok, had some trouble getting this working on the HD2. Working with Racelogic support they figured out that the HD2 needs more parentheses in the formulas than what excel or the testing tools need. So I will update for next time - but you can see a broken version in action here (left turns kinda work, right turns do not).

 

That looks like a great idea!

Is there some general conclusion you can draw about placement of parenthesis in math formulae for the VBOX Video program?? I seem to have problems saving and then re-opening files only to find the formulas garbled -- its like the expressions were compiled to an intermediate format and the file opener can't restore it back to original form. I notice that opening your example files I do not observe the same issue...wondering if it's related to parens(?).

Were you able to get Racelogic folks to consider adding vertical accel to the available channels during this conversation?? Seems like that would be a good improvement for your clever usage here and it ought to be easy for them since it doesn't require CAN decode.

 

I forgot to ask about the Z axis accel, thanks for reminding me!

This is what racelogic sent back to me with additional parens.



This is what I had originally:

 

I could be thinking about this incorrectly, but if you can get yaw angle or yaw rate, you could calculate the acceleration of the yaw angle which "should" give you the z axis g-force.

Also, i'm not entire sure how useful it would be though. My assumption would be as the z axis acceleration increases, theoretically I would expect the lateral g force to decline since you would be seeing slip. In that case, with an extreme Z axis g force, it would already be represented in a reduction of the lateral g force reading.

EDIT: What might be interesting to see if you can get steering angle is to compare the loading on the front tires with the steering input and direction of travel. You would expect to see increasing load on the front tires with steering angle. Whenever you see the drop off of loading on the front tires, the difference between the steering angle and direction of travel would be the optimal slip angle.

Once again, I could not be thinking about this correctly, but might be worth a think.

 

So I was misunderstanding what you meant by Z-axis. I was thinking rotational acceleration about the Z axis. I think according to what you're looking for (if I simplify):

Lat G: acceleration in the X direction
Long G: acceleration in the Y direction
Vert G: acceleration in the Z direction

That being said, the Z direction acceleration (g-force) doesn't change. It's always 1 G. The force you feel in the Z direction on a banking is actually in the X and Y relative to the earth and wouldn't be captured by a pendulum G sensor.

But if its a gyroscopic G sensor, then you wouldn't have to worry about capturing the Z axis G force.

It's been a while since I've thought about this stuff, so once again, I could be wrong.

 

I talked with racelogic today over email. Video vbox units do not have accelerometers, they double diff position data to get acceleration. I didn't know this, but now that I think about it, it makes sense, that the vertical acceleration would be difficult to make accurate due to bumps and the fact that the elevation changes are at a much smaller velocity relative to ground position velocity.

That said, there is no reason why an external sensor could not be used for vertical acceleration, or perhaps the ECU has something.

 

If you could log suspension deflection, you could use the shock/spring info to calc the tire load.

 

Yup, that would be a great way to do it. i'm not that hard core (yet). There are probably some ECU codes that would give similar info - the GT4 has a LCA position sensor on all corners. At some point I am going to convince Racelogic to give me the keys to hack into vehicle can buses.

 

That would be awesome, but I think they might not like giving up that info lol

PM if you're interested with some help for some of this. Porsches are new to me, but I'm have an mechanical engineering background and was coding for my last job, so this seems like something interesting.