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Using opamps to derive the voltage drop across the motor resistance, and subtracting it from the motor voltage. The yelds the voltage resulting from the back EMF and hence the revolutions.
* Motor resistance is: Rated voltage / start current -> 10 V / 10 A = 1 ohm (for the ease of it. Not unrealistic though).
* Voltage to rev. factor: Rated revolutions / rated voltage -> 10 krpm / 10 V = 1000 rpm/V (again, for the ease of it, but still not unrealistic).
This works for various loads and EMF constants, but if the any of the parameters above are changed, the opamp gains must be changed accordingly, which is possible.
This approach may not have any real application, since better ways, such as a tachometers exist, but it's nice to have a way in this simulation tool.
My other designs:
Colpitts Oscillators
http://everycircuit.com/circuit/6472095956729856
Binary LC Filter Bank Oscillator
http://everycircuit.com/circuit/5849640909144064
LC Filter Bank Oscillator
http://everycircuit.com/circuit/6141020952854528
RF Up and Down Mixing
http://everycircuit.com/circuit/6321309163454464
DC Motor Rev. Sliding Mode Controller
http://everycircuit.com/circuit/5398415189213184
Amplitude Modulation and Demodulation
http://everycircuit.com/circuit/5510207106187264
Boost SMPS Unlimited Voltage Build Up
http://everycircuit.com/circuit/6448454909034496
High Power Charge Pump w. Mosfets
http://everycircuit.com/circuit/5016778832084992
Transformerless 230 Vac to 10 Vdc
http://everycircuit.com/circuit/4981362800197632
Motor Revolution Controller
http://everycircuit.com/circuit/6424781689978880
Motor Current Sliding Mode Controller
http://everycircuit.com/circuit/5502940846751744
ΣΔ ADC w. Result Displayed
http://everycircuit.com/circuit/4549196269223936
300W Class D Amplifier w. Mosfet output
http://everycircuit.com/circuit/5452375043342336
Three Phase Star Δ Safe Relay Wiring
http://everycircuit.com/circuit/4748634531037184
Accidental 555 High Voltage Generator LOL
http://everycircuit.com/circuit/5057154477457408
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