wonderer wrote:Bathtub wrote:What kind of instrumentation.... hmm I'd like to see a strain gauge on each corner transmitting real time weight on each wheel. On my outlaw car I played with the COM, not front to back or up or down but left to right. I have no proof but I think that might have been the deciding factor in my winning.
I may well be wrong... (Mechanical instrumentation isn't really my thing.) But wouldn't two 3 axis accelerometers allow for extracting nearly as much relevant data as strain gauges on each corner? It looks like the strain gauges would be doable, but I suspect they might be a calibration nightmare. Like I said though, I'm pretty ignorant about applications for mechanical sensors, so tell me what you'd be looking for in the way of interesting data from strain gauges.
Sorry I wasn't thinking mechanical but electrical. The tiny circuit board inside a Load cell is sometimes refered to as a strain gauge. It is membrane thin and would allow for a very accurate measurement of force on the corners.
Stolen from an Omega website
"What is a Load Cell?
A load cell is a transducer which converts force into a measurable electrical output. Although there are many varieties of load cells, strain gage based load cells are the most commonly used type.
Load Cell History
Before strain gage-based load cells became the method of choice for industrial weighing applications, mechanical lever scales were widely used. Mechanical scales can weigh everything from pills to railroad cars and can do so accurately and reliably if they are properly calibrated and maintained. The method of operation can involve either the use of a weight balancing mechanism or the detection of the force developed by mechanical levers. The earliest, pre-strain gage force sensors included hydraulic and pneumatic designs. In 1843, English physicist Sir Charles Wheatstone devised a bridge circuit that could measure electrical resistances. The Wheatstone bridge circuit is ideal for measuring the resistance changes that occur in strain gages. Although the first bonded resistance wire strain gage was developed in the 1940s, it was not until modern electronics caught up that the new technology became technically and economically feasible. Since that time, however, strain gages have proliferated both as mechanical scale components and in stand-alone load cells. Today, except for certain laboratories where precision mechanical balances are still used, strain gage load cells dominate the weighing industry. Pneumatic load cells are sometimes used where intrinsic safety and hygiene are desired, and hydraulic load cells are considered in remote locations, as they do not require a power supply. Strain gage load cells offer accuracies from within 0.03% to 0.25% full scale and are suitable for almost all industrial applications.
The acctual wheatstone bridge circuit for this application is printed on a membrane in most cases. Very small, and could be taped to the car.
Just sitting here comptemplating. I guess I could find out what I want to know if I had four scales, one for each corner but would never really know unless I could measure the weight in motion. The car would have to have some sort of suspension all be it would have to be hard. At this size you might have to make all your instrumentation from hand. This I think would give you a good idea of what part COM and aerodynamic's play.
I can understand the three points of vibration, but without knowing the forces at the corners while at speed and trending them agaisnt the vibration will you see a true picture of what the car is doing.
An example would be a bump on the track, You should see a change in weight all for corners, change in vibration (At least 2 axis) and a reduction in speed. With these variables you should be able to massage a car to perfect speed.
