I have long wanted to datalog the amount of lift I get at the rear of my lakester. I did fabricate a switched LED gizmo on the front axle to see if there was any significant lift up there but, later, I realized that the spring rate up front is over 1800 lb/inch and there won't be any movement between the axle and frame at this end of the car. Which isn't saying there isn't lift, just that I can't measure it.

I've pondered many schemes for monitoring lift in the rear, even bought some parts to connect a spring-loaded potentiometer with a cable running over a drum down to the axle housing. Complicated, and requires tools not in my shop. Or even an indicator like Dan Hostetter installed in his streamliner. He used a morse cable mounted on the frame with one end fastened to the axle and the other sticking up in the air in the cockpit in front of him. He put a small piece of foam on the rod and pushed it down flush with the cable housing end. As the car lifted, the cable would pull in, sliding the foam up the rod. At the end of his run, with the car back in equilibrium, the distance of the foam piece from the cable housing end was the maximum lift the car had experienced. Simple, yet quite effective. And, since his purpose in building and modifying this car was to experiment with aerodynamics and, in particular, handling at speed, quite necessary information.

Ran across an infrared distance sensor on-line. This handy gadget measures distance to a reflective object in a strange, yet effective way: The LED on the left emits light. The thing on the right that looks like an LED is actually a lens; the light reflected from an object is focussed on a CCD strip behind the lens. The pixel with the strongest signal is proportional to the angle of the reflected light. As you undoubtedly recall from HS geometry, if you know the subtended angle and the length of the base, you can calculate the distance from the base to the point of the triangle -- the distance of the object.


The output is a voltage -- handy for datalogging -- but it is not linear, of course. It involves trignometry and some constants that I don't know. However, the datasheet has a graph of output voltage versus distance (actually versus inverse distance), but I think I'll just make some measurements of my own and, over the small changes in distance I expect (hope) in this application, I can probably come up with a linear scale factor to turn volts into lift in inches.

This guy runs on 5V, which happens to be available from my datalogger. Outputs a voltage in the span 0-5V. Should be very simple to mount, all I have to do is paint a white patch on the differential housing for it to reflect from.

Oh, yes. It costs $15!