LM-1 as poor mans windtunnel

[klatinn]

Hi,

I saw a lot of discussions on this board about the effects of different tails and so on, specially with respect to downforce. Here's a suggestion how to datalog downforce while driving.

Needed:
2 stroke-pots for front and rear
car with swaybars front and rear
LM-1 with RPM converter or Auxbox.

Fabricate a little clamp-on lever to clamp to the center of the swaybar. The lever will be connected to one side of the stroke-pot. Other side mounted to chassis.
Supply stroke pots with 5V. Mount them so that with the car at rest they are about halfway pushed in.
To calibrate, put the car on a level surface. Load the rear or front up with 50# sandbags positioned over the axles, one at a time and note the stroke-pot voltage as the car sinks into its suspension. You can do that with LogWorks also
Then enter the voltage/# equivalents in a LogWorks lookup table.
Do your test-drive on a smooth track. With RPMs logged and known gear you can calculate speed and directly look up downforce vs. speed, using the cars suspension as the force-measuring spring.
Use the LogWorks smoothing function to average out the effects of uneven surfaces. Measure at constant speeds as acceleration or braking loads the cars rear or front.

Regards,
Klaus

[304065]

Klaus, great idea!

It seems that anything that can be reliably measured with a potentiometer is susceptible to measurement and logging.

I suppose driver's heartbeat and body temperature are feasible too.

[deoxford]

LM-1 is a sort of sensor I am quessing can you tell me what it does?

[klatinn]

Hi John,

Actually I want to go a step further. With the LMA-3 you can log accelleration with variable sensitivity. Set the sensitivity to 0.25g. Then drive the car on a level track (no wind) up to a certain speed and drop the clutch. Datalog the coast-down. From that the coast-down speed profile can be calculated. A second order polynomial function can be fitted to this coastdown log.
The polynomial has the form:
A*v^2 + B*v + C.
The A constant is your aerodynamic coeff (frontal area * ca) . The B constant is gearbox drag coeff (which is roughly proportional to speed) and C is rolling resistance. This should give additional info about aerodynamics.
I am adding all the calculations and curve fitting to the next LogWorks version.

Of course drivers heartbeat and temp can be logged as well. Just use the appropriate sensors. But I don't want to elaborate

Regards,
Klaus

[304065]

http://www.pelicanparts.com/catalog/shopcart/911E/POR_911E_fuelij_pg5.htm#item31

[klatinn]

Originally posted by deoxford
LM-1 is a sort of sensor I am quessing can you tell me what it does?

Look at the top of the screen. It's a hand-held wideband air-fuel meter and 6 channel datalogger. Logs internally 6 channels at 12 datasets/second for 44 minutes.

[ChrisBennet]

Originally posted by klatinn
Look at the top of the screen. It's a hand-held wideband air-fuel meter and 6 channel datalogger. Logs internally 6 channels at 12 datasets/second for 44 minutes.

The banner ad at the top of the page changes, sometimes it's the LM-1, then Wayne's book, the Alden Wrench, etc.
-Chris

[Wayne 962]

http://www.pelicanparts.com/catalog/shopcart/MISC/POR_MISC_INNOVT-detail.htm