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Recent content by dford

  1. dford

    Accelerometer to get Position

    Ina: You will save yourself grief if you take a look at some of the articles relative to inertial navigation errors available on the web. Perhaps you should consider GPS solutions? Good Luck, Doug
  2. dford

    WARNING! Excel order of operations problem...

    Swearingen: It is good that you warned the forum about the Excel math problem, you probably have had some small (positive) impact on the nations technical productivity. I can imagine your confusion before you resolved Microsoft's error. Quattro, which I use, interprets the math correctly...
  3. dford

    4-bit binary counters

    I have fond memories of the old Brush strip chart records produced by the 100 Volt Beckman Ease, but I don't miss the sore fingers associated with plugging up a big patch panel. Problem solutions always seemed more tangible in the analog lab then they do now with systems like Simulink. Anybody...
  4. dford

    Educational standards ??? What standards ??

    I don't think we should be surprised by this report. I suspect we would get similar results from testing government employees, elected officials, sports and media people. Education focused on test standards gets this kind of result. The people who write the policies and standards seem to...
  5. dford

    Aerodynamic coefficients for a production car

    Thanks Greg: It is interesting that the NACA and SAE symbology is so different. Even marine, SNAME, is close to NACA. NACA yaw moment coef is CN and derivatives are CNx. Lateral reference length is usually the wing span. Longitudinal point of reference is usually .25mac. Doug
  6. dford

    Aerodynamic coefficients for a production car

    Greg: I don't know about SAE aero convention, but in NACA convention CYx is a side force derivative. As to the dimensional problem, remember that moments are nondimensionalized by an additional characteristic length that doesn't show up in the force coefficient dimensionalization. Just...
  7. dford

    How do I accurately measure moment of inertia of a small motor rotor

    Horder: There is an old method called the bifilar-suspension method. Suspend the rotor from two strings length L, seperated by distance 2R. Displace rotor a small angle to wind up the suspension, release and measure the frequency of oscillation, f. The inertia is: J = WR^2/((2pi*f)^2 * L)...
  8. dford

    Greatest physical misconceptions

    It is common for people to think that vacuum does work and that "cold" flows toward warm. Doug
  9. dford

    impossible transfer function 1/1-s

    gogo: To illustrate the trap I mentioned in an earlier post, try this: Start with a stable plant, say 1/(s+1). Compensate with your phase lead filter and gain K say, 2 K/(2-s). So the open loop system TF is 2K /((s+1)(2-s)). If you plot the Bode for this open loop system you might say...
  10. dford

    slope of a tangent

    JB: (1/u)(du/dx)|2 = 25/53 Doug
  11. dford

    Marine 2 stroke engine is dead ?

    Jet: Evinrude has committed to two stroke. They have a design they call etech. It looks to me like it is the engine to watch. Very low emission, light weight, responsive to throttle. Doug
  12. dford

    [ponder] Driving torque for variable inertia

    mike: It turns out that the energy equation you used is not valid for a variable mass system. For fixed mass translational system d(KE) = F dx , like you tried to use. KE is kinetic energy 1/2mvv. For variable mass system d(m Ke) = m F dx Found reference to a similar problem in Goldstein's...
  13. dford

    US engineers need to be trained more like Asian and European counterp

    Maybe GM management needs some training as to what the engineers do. (Good luck to the trainers.) Seems pretty wastefull to train the electronics, software, thermodynamic, metallurgy, aerodynamics, etc., guys to become efficient draftsmen. Doug
  14. dford

    impossible transfer function 1/1-s

    gogo: Be wary of intuition when dealing with stability of systems. Uncritical application of frequency domain methods when dealing with nonminimum phase sytems can be a trap. Write out the complete system open loop transfer function, including the (management proposed) compensator and use root...
  15. dford

    impossible transfer function 1/1-s

    gogo: Yes, you can build it easily; at most 3 op amps and a cap and some resistors. You will get the voltage transfer function you desire. The circuit won't be stable. You can build an aux negative feedback loop around the circuit to stabilize it and drive the outer loop with a sinusoid -...
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