Here are some of the results of a few experiments I did on my climbing robot carriage to see if I could get it to climb the pole faster. Using the original design the carriage climbed a 6 foot pole in approximately 3.5 minutes.
1. Use a large motor in place of the small motor.
The large motor has max speed of 43 rpm and a stall torque of 23.53 in/lbs. So much more powerful than the small motor. Using the large motor the carriage climbed significantly faster but it also revealed another flaw in the design that made it impossible to complete the climb. The flaw? I used some pulley wheels taken from my erector set. The grooves in these pulley wheels was not deep enough for the climb rope and the rope slipped out of the pulleys causing the carriage to crash down. Another issue caused by the increased speed is the way the rope wound around the axle. The rope would bunch against the wall of the carriage and jam in the axle hole. Fixes for these 2 problems can be found in a subsequent post. The results of this experiment, even though it failed, were encourging.
2. Remove the pulley wheels and reverse the gearing to get more speed
One of the things that was obvious from the first experiment was that the large motor probably had enough power to lift the carriage without the additional mechanical advantage of the pulley system. So in the second experiment I removed the pulley system and changed the gearing so that speed was increased rather than torque. So instead of the motor driving the small gear and the axle having the large gear meaning the motor would have to turn the small gear 7.2 times to get 1 revolution of the large gear (the axle), I have the motor driving the large gear and have the small gear attached to the axle. In this configuration one revolution of the large gear would generate 7.2 revolutions of the small gear (the axle). In this configuration again the carriage began climbing the pole very fast and again I hit a problem. This time as the carriage climbed the belt between the gears began to slip. Another failure… This one can be fixed by controlling the speed of the large motor. I can do this in 2 ways. 1. add a linear potentiometer 2. program the VEX cortex that I’m using as the micro-controller. I will experiment with these 2 solutions in the next week and provide the results in a separate post.
3. Just use the large motor to drive the axle directly.
Again, based on the 2 previous experiments, it was clear that the large motor could lift the carriage on its own. So in the third experiment I configured the large motor to drive the axle directly, no pulley system and no gearing. In this simple configuration the carriage climbed the 6 foot pole in 34 seconds. A lot faster than the initial small motor configuration.
As usual, the simplest solution is usually the best! ;o)
Ultimately, if the carriage is to actually do something other than climb the pole it will have to be able to lift more weight. A solution that includes the pulley system, speed gearing, and a way to control the large motor speed (programming the micro-controller or using a potentiometer) will be needed.