Quote:
|
Originally Posted by Greg Needel
it really isn't limiting the power of the motors. since the IFI setup uses pwm(pulse width modulation) the motors are still receiving maximum voltage, it is just the pulse length that is shorter. and since
Torque(transmitted to the shaft) = (Horsepower*63000)/rpm
and since 1 HP = 745.699872 watts
and watts= voltage^2/ohms <--constant in this case because resistance of the motor doesn't change and neither does the voltage.
the total torque transmitted at a given rpm is the same, all that is being changed is your speed. This is the same thing that happens when you push the joysticks only a little bit forward.
we did this this past year and it works very well for precise movements on the field.
although to make a "speed boost" button you would have to be limiting your pwm the whole time except when you want to boost, which would be a waste.
|
First, you should check your formulas. "Watts" = Voltage^2/R (and note that "Watts" should really be Power) is the electrical power to the motor. Considering it is not perfect, there are lots of losses and the mechanical power available at the motor output is omega times torque.
They're not the same and the electrical power (supplied) will always be higher.
Second, the PWM does change the voltage seen by the motor. Even though you are pulsing it between 12V and 0 V, the motor can be seen as an RL (resistor-inductor) series association and thus this pulsed voltage is smoothed and you get an average voltage that is proportional to the PWM duty cycle. I don't want to extend and there are lots of old posts about it, good information can be found there.
When you change the voltage to the motor, you can simply scale its speed/torque curve by a factor of (applied voltage/test voltage), so you are actually changing both its speed and torque (and power, as a consequence).
Concerning the speed boost, we used that one year. It sucked.
The only possible use I see is to make a very fast robot a bit more controllable, but then again your gearing is probably wrong and you are (again) wasting power.
To me, the "coolness factor" of this solution can really hinder your performance.
If your opponent is coming at you with 4 CIMs full power, why in the world would you want to get in a shoving match with your robot at 70%?