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TeamUR Robo-Project Illustrated

As before the robot "heavy construction" has started from building the suspension. Since TeamUR the First was not well controlled because of different mechanical characteristics of the motors we decided to try stepper motors to propel the robot.
Another important decision was to go for subminiature plastic sprockets and chain.

We considered couple of possibilities as on the drawing:

Finally we decided to go for the solution E, in which the sprocket attached to the motor "covers" the motor because of the bigger diameter.

Here is our hero: stepper motor for $1.25 (item: SMT-39) from All Electronics.
Four lead, bipolar stepper motor. 0.78" diameter x 0.73" high. 0.058" (1.5mm) diameter x 0.36" long shaft with small press-fit gear. 2" long leads. It makes 16 steps per revolution.

The problem is that we don't know too much about it. It has been initially selected because of its relatively small diameter and first of all the price.

	What was the original purpose of the motor?
	What is the nominal working voltage?
	What is the motor's torque?

If you know answer to any of those questions please let us know.

Now we have a task to attach the sprocket to the shaft. We decided to leave the gear. The easiest way to accomplish the goal is use some tubing and glue it to the gear. But how to do it to not make it out of center. Here we used an epoxy glue, which filled the tubing and allow to install it on the gear.

Here we have the tubing finally glued to the shaft with gear.

Some sand paper work decreases the differences in inside sprocket diameter and outside tubing diameter.

Now it is time to cut the brass side plate and make couple of holes for the motor.

Again, the tubing helped us to install the other sprockets. The brass tubing was easily soldered to the brass side plate.

It looks like we have everything to mount the sprockets and the chain.

Wow! This is impressive! Looks very professional, doesn't it?

The stepper motor controlled by test circuit pulled the chain! The main problem we noticed was that the chain was too loose. Perhaps it will require kind of tensioner... Sounds like unnecessary complication.
The other thing, which was our concern was that the motor is not enough precise. For the whole revolution requires approximately 16 steps. Therefore we have 10+ degrees by step and 3+ mm of the linear motion (let us to not convert those millimeters to inches :o) ). It looks that the motor sprocket is too big for this low precession stepper motor... Unfortunately high precision motors cost at least 100 times more (!).

We see now the potential problems: the robot, if the motor has enough torque will be jumping step by step. The possible solution could be decreasing of the motor sprocket size and using bigger the traction sprockets.

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.