Thursday, September 07, 2006


Beginning Tommelise

Now that I have an operational pseudo-stepper motor and working control board philosophy to power a small-scale RepStrap, I am beginning the Tommelise project. For those of you who don't read your Hans Christian Andersen in the original Danish, the tale of Tommelise is better known in English as Thumbelina. I've always preferred the original name over the English transliteration. Mind, the transliteration wasn't bad. Tommelise would have come out Thumblisa. The translator did a good job.

I have a lot of both material and experience from building Godzilla that I think will be useful in

I'm going to be staying with milled poplar and making more use of 1-1/2 x 3/4 inch cross section modules.

I've got 3/8-24 (0.95 mm metric pitch) and 1/4-20 threaded steel rods
(0.79 mm metric pitch) which should be adequate for the dimensions that I am looking at. Both diameters mate fairly well with the GM8 gear motors that I will be employing. I will probably use 3/8-24 for the z and x axes (horizontal) and the lighter 1/4-20 for the y axis (vertical).

Going with Reiyuki's CNC gantry philosophy should allow me to use the same axis design for at least the z and x axis and probably also for the y.

My first task this weekend will be to knock together a z-axis platform to see if the GM8 is going to be happy turning that 3/8ths inch threaded rod. I'm not too worried about that since the GM8 has a considerable amount of torque, but I'd like to be sure all the same.

What are your planned XYZ working dimensions for this design?

Also, do you have any guess as to expected max/min movement velocities?
What are your planned XYZ working dimensions for this design?

I'm going for 300x300x150 mm for this one.

As designed with the parts at hand I'm looking at 0 - 1.0 mm/sec. Now that I can make a gearmotor emulate a stepper I can get that bottom velocity down to 0 properly.

I'm supposed to be getting a faster and more powerful gearmotor form Solarbotics in the next few days.

With a working Tommelisa I will be able to make gear trains. That should be no problem since Tommelisa 1.0 will have an accuracy of 0.025 mm.

First move is to build some gear boxes for the horizontal axes to kick the speed up a bit. A translation speed of 4-6 mm/sec should get us an economically viable machine. My first attempt at that will be to try to do it with gearing. If that doesn't work, I have things like panthgraphs to try.
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