Hi there everyone and merry xmas to all...In certain treadmills, the speed by which the user is running is measured and calculated using a mounted sensor near the rotor of the motor. However I found that some treadmills lack this sensor, and I am seriously wondering how this could be achieved? I know that the more the motor is rotating, the more current it consumes, but I hope to know the formula relating electrical quantity(ies) to the rotation per minute (rpm).Thanks in advance...
If the treadmill has a DC motor, the speed controller's output voltage sets the motor speed. If the treadmill has an AC motor, the speed controller's output frequency sets the motor speed. Both types of speed controllers can control the speed reasonably well without feedback. PS1 The speed indication display is based on the controller voltage or frequency if the speed is not measured to provide feedback. PS2 Motor current is an indication of the torque that a motor is producing. If the voltage applied to a DC motor or the frequency and voltage applied to an AC motor are held constant, the speed generally decreases from the no-load value as the motor is loaded. That provides a way of determining the speed more accurately than just assuming that a certain applied voltage or frequency results in a given speed. The details of analyzing motor performance vary a lot depending on the motor type and design.
quite a lot depends on the motor in question. if you've even seen power company generators, they don't turn very fast, yet they generate millions of watts. your best bet is to get a brushed motor that has permanent magnets, and just test. induction motors won't work. motors with stators that are powered by the current, rather than permanent magnets won't work. and you'll need an ammeter that's appropriate to the current you're generating.
There are circuits that can do that but not easy to explain in detail here. The idea is to remove power from the motor momentarily and measure back emf voltage which is proprotional to motor speed. This is generally done periodically to determine motor speed. In this way a controller can adjust the motor speed. This method is not suitable for AC motors.
