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TeamUR Robo-Project Illustrated

TeamUR the Second got a nickname: "Jerky"!. The first experiments with the stepper motor attached to the test circuit looked very promising. The motor was easy to control and didn't make any trouble. Unfortunately after loading the robot with the battery the whole construction became to heavy. The stepper motor just got stuck and was not able to pull the chain.

	The first obvious thing to do was to install much smaller sprocket on the motor's shaft (compare with the the previous robot look). It helped but not too much. The robot's motor was able to move the chain with the battery charged above 80%. Later on the battery voltage is dropping sometimes below 6V what gives some problems with +5V stabilizer. Thanks to PIC's robustness it doesn't make a big difference in this simple circuit.
	Because of the nature of a stepper motor and rather low precision of the one we have a single step causes relatively big chain movement. It is the reason why the plastic chain has not enough grip and just slips on the floor. Installing four grommets helped again but not fully. The robot requires FRESH battery and high motor rotation. Slow stepping, what was our goal just is not possible. Even more improvement has been noticed after replacing the chain with rubber band. It gave us idea that the band was acting as a mechanical micro energy accumulator. It was absorbing the step energy during rapid shaft movement and slowly releasing it when the shaft was already stopped.
	The lack of tensioner requires some position adjustments of at least one sprocket. The holes used to mount the motor needed to be increased with file to this oval shape.

It looks that we have a lot to think about.

	How to increase the torque?
	How to decrease the power consumption at the same time? The theory of stepper motor control suggests powering the motor all the times. We think that it is not necessary in our application where there is no load between steps (perhaps except the case where the robot is climbing the upgrade). It must be a minimal pulse length, which can move the motor from one position to another. The rest of the time (between consecutive steps) the motor probably can remain not powered. Is it true?
	Is it possible to achieve these two contradicting goals?
	It looks that stepper motor dynamic movement (fast steps) looks different than moving slowly step by step. Where can we find a description of those phenomena?

TeamUR Robo-Project Illustrated

All rights reserved. For problems or questions regarding this web contact [Project Email]. Last updated: May 27, 2004.

All rights reserved.
For problems or questions regarding this web contact [Project Email].
Last updated: May 27, 2004.