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Adding a Switch for Direction Reversal in 12v DC Motor W/ PWM Controller System

Figure 1. Modifications required.You can reverse the motor with a double-pole, double-throw (DPDT) switch.Be careful with this. Reversing the motor while at speed will cause high currents to flow as the momentum of the motor must be overcome to reverse it

1. How diodes protect H-bridge DC motor driver?

To supplement Anindo's fine answer, specifically, the voltage across the inductor (i.e., in this case the motor) is \$\$ L fracdidt \$\$Thus, when current is cut off suddenly (exactly what an h-bridge wants to do, especially when controlled as a PWM), \$fracdidt\$ gets extremely large and there is an associated very large spike in voltage. The diodes protect the MOSFETs from these spikes.

2. Can a DC motor be of specification 320Watts, 3A, 24 V?

Sure, they can print anything they want on the sticker. As you noticed, \$24:mathrm V cdot 3:mathrm A = 72:mathrm W\$. To get 320W in any sense (mechanical, electrical, or thermal power) would require more voltage, more current, or both, or a violation of the law of conservation of energy. One then wonders, how do they get 320W?My guess (since the sticker is too brief to say): "320W" is the maximum theoretical mechanical power this motor could produce.A DC motor driven by a fixed voltage has a maximum no-load speed, and a maximum torque which is developed at zero speed. That maximum no-load speed is limited by the battery voltage (here, 24V), and the maximum torque is limited by the stall current, which is not specified but which is probably (a lot) more than 3A. You can get a rough idea by measuring the winding resistance with an ohmmeter, then calculating what the current would be into that resistance at 24V with Ohm's law. Sometimes you have to jiggle the rotor to get the commutator to line up.A linear function then describes the torque vs. speed relationship for a given motor, at a given voltage. From Understanding D.C. Motor Characteristics:Mechanical power is the product of torque and speed, and thus, the motor develops maximal mechanical power at the midpoint of this line, where the motor is running at half its maximum speed and delivering half its maximum torque."320W" likely refers to this maximum theoretical mechanical power. Of course, the motor will overheat if you actually run it under those conditions for very long. Briefly however, it will be fine, as long as you do not generate more heat than would be generated by 3A continuously, or generate so much torque as to damage the motor mechanically

3. i want to make a dc motor which should run on 10v.?

I would use thirteen.5v at 1.Zero amp. I might location a resistor in sequence in line between the source voltage and the three fans wired in parallel. You are going to need the series resistor to drop 1.5 volts throughout it. The present flowing via the resistor should be (a hundred thirty ma one hundred thirty ma 130 ma) or 390 ma (0. 390 amps). For that reason, 1. 5 v / 0. 390 amps = 3. 85 ohms (use 4. Zero ohms) rated at I^2 x R (0. 390 amps ^2 x 4. 0 ohms) = 0. 600 watts (use 1. 5 watts). The in line resistor must then be 4. 0 ohms at 1. 5 watts. The adapter should force the three parallel lovers just best

4. Strongest DC motor I can find in the 1-1.5 pound range?

Power is speed times torque, so you need either high speed or high torque. If you use a high speed motor, then you need a high speed gear box, which wo not be cheap. Anyway, the most powerful motor will be one that uses Neo permanent magnets, but its not real cheap. For this small size a DC machine will probably be the best choice

5. PID control at small PWM values for a DC motor

You have backlash in the gear train which is like electrical hysteresis. That is causing "hunting". You can minimize the backlash by preloading as in anti-backlash gears. You can adopt a simpler control scheme such as P (perhaps with some control deadband) or PD. The integral term, if present, will integrate any remaining error until motion occurs (unless the I term has deliberate or accidental deadband itself - say due to low ADC resolution).You might want to read this paper by Tim Wescott. Tim does a lot of work with precision electromechanical systems used in military and similar applications.

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