Quote:
Originally posted by AllenH
However, team 111 has had huge success by limiting the speed control to only 50% when you want to move slower. Only when we want 100 percent by push of the thumb button on the joy stick, we speed off. It's all about the proper gear ratio. There are ratios to maximize speed and power with each motor. You just need to know the magic number 
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You can get a good Tourqe:Speed ratio through gears yes, but you can change it for higer torque or higher speed through shifting gears.
There are two real ways to shift, 1) Shift the planetary system in the gearbox of the drill motor. 2) Shift actual gears in your gearbox after the motor.
Having X ratio and giving it 50% power will not give you more pushing force, it will only slow your speed. The advantage to limiting power is less draw on the battery, and less chance of overheating your motor. You will NOT gain tourque by supplying less power.
If you look at the power curve for the motors, they are all in accordance to 12 volts being delivered. You can, for the most part, just shift everything down by about 1/2 to see what your speed and torque would be at 50% power. If you change gears however, you'll shift the curve to the left or right.
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On the topic at hand..
There are 2 good ways to go about shifting.
1) Servo motor - Turn the servo and it worms the shifter over to a new position. Doesn't take much torque to slide, and the servo doesn't provide much torque.. beatiful combination, rather imple to make with a pretty wide tolerance.
2) Small Pneumatic cylinder
a) above each motor's shifter you can mount a small cylinder that is attached directly to the slider. Pneumatic extends, motor shifts. Program in to not allow motor to be moving to fast when shifting or a nice grinding sound might be heard. And grinding is never a good sound.
b) If the motor's are in line with eachother, you can have a single cylinder mounted above them both. When it extends, it pulls both pins, shifting both motors. You'll have to engineer a bit more with this one so that they both shift to the same gear. If the motors are facing oppisite directions and get the same linear force, they will shift into oppisite gears. (One low, one high). There are ways around this, such as flipping one motor around (which hurts on space) or a reverse pusher. (Reverses force on another bar to change force and shift gears in oppisite directions and same gear.)
c) Within each gearbox, after the motor, have a cylinder actuate a shaft of gears into another position. This works on the same concept as a car's transmission. When cylinder is retracted, gear "a" is being rotated by gear "b". When cylinder is extended, gear "c" is being rotated by gead "d". a and c would be on the same shaft, and gears b and d would be on the same shaft. I don't have any diagrams to show this, but if you hunt around you'll find it.
d) (I saw this in 469's gearbox last year and thought it was a very neat idea). Have the gearboxes in the same orientation as eachother, but the shifting gear (a, c above) be oriented differently. When the cylinder extends, it pushes a and c's shaft to interact c to d. mount a shaft to extend with the cylinder so they both get actuated. If you need more information I can draw up a diagram or contact team 469 about how they did this.