Mount pen on BoeBot ActivityBot chassis

John Kauffman

My students have been drawing polygons with Boe- and ActivityBots. The pen sits in a tube strapped to the front of chassis. The problem is that with every turn the bot draws a tooth sticking out from the polygon because the pen is offset from the pivot point.

I'm thinking of drilling a hole through the chassis at the center point between axles and mounting a tube rising up between the servos. The tube can't come up out of the bot like Scribbler due to the board. But maybe I can fit in a broken-off pencil or some kind of short novelty marker. Or I can try some longer spacers to raise the board.

Has anyone hacked a chassis to get a pen/pencil at the pivot point between axles?

Thanks

Keith Young

A couple students put the pen right by one of the front wheels. With clever turning you can get better drawings that way.

Not perfect, but it beats drilling the chassis.

Ultimately the S3 will be a much better bet in my opinion.

John Kauffman

Thanks. In that scenario we write the code with all turns pivoting on the pen wheel. I'll give it a try.

MikeDYur

John, you don't really need the whole pen, just the inside; which you can placed in a drilled out block of wood. The pen refill can be curled over underneath, and the block of wood can be mounted between the two servos under the chassis with double sided tape.

MikeDYur

A pic of the flexible pen insides

MikeDYur

Here's a quick sketch of what I was getting at, sorry didn't have much handy at this time.

MikeDYur

Take it a step further, and you can get the kids involved, if the blocks of wood are pre-cut, they can cut the thin piece and glue them together.

Keith Young

That's a cool idea

I'll ask my students this semester to come up with a good way to make the ActivityBot draw and see what they come up with. Might get some creative solutions.

MikeDYur

Keith Young wrote: »

Might get some creative solutions.

One could be a stainless steel extension to lower weight, tubing from dipole antennas can be used as conduit and glued in place.

VonSzarvas

Another solution just came to mind.

Leave the pen mounted on the side of the BoeBot, but have it servo controlled to lift up-and-down whilst turning.

This kit caught my eye: PING))) Mounting Bracket Kit

Mounted sideways, it might be enough to rotate the pen up off the paper....

This might necessitate always drawing in the same direction (as the pen tip will in theory be at an angle to the paper, and so kinda dragging along). However, that seems like a great code challenge for more advanced students; and as you can lift the pen, then rotating the BoeBot as required to draw in the same direction ought not be an issue.

Optimising the servo control code with encoder feedback will likely improve results greatly, and that is also going to provide a few more classes for eager students. Maybe even an entire term! With final objective to have BoeBot accept text input wirelessly, and draw that text as accurately as possible onto paper (or rolls of paper), in the font size of your choosing! Massive Banners for school prom.... no problem!

John Kauffman

Mike:

I had always pictured that in the end the pen or marker would have to be cut short to fit under the board. But your idea is great - cut it even shorter and fit under the chassis.

I can cut pencils down to 5cm.

Thanks for the leap of thought that makes the solution easy.

John Kauffman

Von:
I agree, cool idea.
One student had suggested a servo mounted with horizontal axis and a wheel with multiple markers coming out from the wheel. The servo would rotate to bring a given color to the paper. That would be tricky. But, as you said, would be a great engineering/coding challenge for the advanced students.
Thanks.

MikeDYur

John Kauffman wrote: »

I can cut pencils down to 5cm.

John,

If you bend the pen innards, it may compress the ink enough to leak from the top, it needs to vent, you will need a solution to protect kids and robots from the nasty stuff.

Whit

John - your missing the point - this the the perfect excuse to buy a new S3 - You need it! ;-)

Kidding aside - this is great idea! I can't wait to see y'all's solution. You could also put an LED on top - dead center and do some time-lapse photography light scribbling. See this thread - especially in this section of what is now a very long thread - http://forums.parallax.com/discussion/160957/nikos-fibonacci-spiral-challenge/p6 or add a line of LEDs and do some dot-matrix printing! http://forums.parallax.com/discussion/163960/the-s2-led-dot-matrix-printer-thread

John Kauffman

Whit:

I agree on getting an S3, but we are not talking about "a." We have 7 BoeBots and more coming in Oct. Also, adding the pen to BoeBots means zero learning curve for a different platform.

Nice links - we have this same idea scheduled for a collaborative project with the art department.

John Kauffman

I spent this morning in a demonstration of our 3D printing lab. I think we will be able to get the drawing of a pen-mounting block and then have that sliced and printed. If it works then I will post the file.

Keith Young

Awesome. Looking forward to it.