PDA

View Full Version : [Project] Line Drawing Robot



arcadefreaque
08-03-2011, 01:05 PM
I'm looking for either someone to build or point me towards a kit that would be relatively easy to construct a robot that can accurately create an off-shaped oval drawing on concrete using chalk. Basically, I need to be able to place the robot on a concrete slab (may have small cracks where it was cut into squares) and draw an oval within an oval. The drawing needs to be precise (within inches) and smoothly drawn. Approx size would be 100ft by 70ft, and the oval would not be exactly rounded (the circular ends would be offshaped a tad).

Quantum
08-03-2011, 02:53 PM
Scribbler Bot by Parallax might work.
The trick would be how to keep feeding the chalk as it wears down.

http://www.parallax.com/Store/Robots/AllRobots/tabid/128/CategoryID/3/List/0/SortField/0/Level/a/ProductID/714/Default.aspx

ROBOTMAN
08-03-2011, 05:38 PM
100ft by 70ft is a long distance! You will definitely need the encoders the scribbler includes to be accurate. A simple way to keep feeding the chalk would be to attach it to a servo at a 120 degree angle then thought the program move the servo closer and closer to 180 pushing the calk against the ground. If the dose not make sense I can provide a drawing.

Quantum
08-03-2011, 07:04 PM
You could go a lot simpler route. Something like a tube with a cap on one end with a spring inside pushing on the chalk so its against the ground the whole time.

Janis
08-03-2011, 07:29 PM
How about just using a string?
http://www.waterfront-woods.com/Articles/Ellipse/stringellipse.htm

arcadefreaque
08-04-2011, 07:14 AM
Thanks for the suggestions everyone. I had thought about the chalk part, and figure I could get come up with something spring loaded, or possibly find another medium (maybe powdered chalk like they use for ball fields? or some sort of marker that cleans up easily?). I'm guessing the robot design would be best if it were a larger bot - something with some weight to it so that it could be scaled and built upon (totally dreaming here - but rather than chalk there are hand-held devices that can be built which a person follows the chalk design and reels out very sticky colored tape on the floor for more permanent 'temporary' markings. It would be superb if the design could be scaled to incorporate this at some point).

My big issue here is accuracy. I'm wondering if a simple line drawing bot would be able to maintain a consistent and accurate line (even through the few bumps as it transitions across the cuts in the concrete floor). Maybe something that would utilize a beacon in the middle of the drawing area (IR, Bluetooth, Wifi, whatever) to consistently tell it's location would help? We actually do this manually with a series of strings, but the issue is that the shape is not precisely an oval (see below. the straight lines through the middle won't need to be drawn, they are just there for measurement purposes)

http://i1208.photobucket.com/albums/cc370/arcadefreaque/design.jpg

Notice that the ends of the oval are not quite the same distance from the center on both sides of each end.

I had thought that if using a beacon (of sorts) was not as feasible, possibly reeling the rope onto the robot and using it as a measurement (letting a known distance of the rope reel out and back in) as it draws the line might be feasible? FYI - I am generally a decent tinkerer, but the concepts of designing something like this are a bit of a stretch for me at this point. My only prior endeavor into a mobile robotic platform was the EVO kit (which was basically a small kit with stepper motors that was driven by a laptop)

ROBOTMAN
08-04-2011, 12:04 PM
I'm not sure encoders alone would give you the accuracy you want especially if the surface is uneven, a slight bounce could send it off track. An IR beacon would work good in conjunction with encoders but most IR beacons only work at a range of 10-20ft like this one:

http://www.pololu.com/catalog/product/701

I think the string is actually the most brilliant idea because it is simple yet affective you would just need to account for the error somehow...

Here is a platform I used for a while that has great encoders and has more weight to it:

http://www.roboticsconnection.com/p-73-stinger-robot-kit.aspx

http://www.roboticsconnection.com/p-15-traxster-robot-kit.aspx

But those are much more expensive and require a separate controller. They work great for expansion though...

cire
08-04-2011, 10:21 PM
How about just using a string?
http://www.waterfront-woods.com/Articles/Ellipse/stringellipse.htm


That was what I was thinking. Maybe you could utilize the old fashioned string method, with a robot.

Stobs
08-05-2011, 12:36 PM
You could do this with a simple grid of steel pipe - and a tape measure of sufficient size (about 100'), that could be disassembled down to a few lengths of 10' pipe and some fittings. You'd just need to have a way of transporting and storing the pieces. Also, they wouldn't need to be more than hand tightened for assemble but sometimes it's easier to have wrenches for disassembly; figure about 30 minutes for either setup and then also for tear down with reduction in both with experience. If this is an option I'll diagram it up and give you a ball park figure for materials.

Regards

arcadefreaque
08-05-2011, 02:53 PM
You could do this with a simple grid of steel pipe - and a tape measure of sufficient size (about 100'), that could be disassembled down to a few lengths of 10' pipe and some fittings. You'd just need to have a way of transporting and storing the pieces. Also, they wouldn't need to be more than hand tightened for assemble but sometimes it's easier to have wrenches for disassembly; figure about 30 minutes for either setup and then also for tear down with reduction in both with experience. If this is an option I'll diagram it up and give you a ball park figure for materials.

Regards
Thanks. I was really hoping for something that I could just take out of the trunk, set down on the floor and walk away while it does its thing (or at least as close to that as possible). Currently, I can do this manually with a block of wood, a rope with tape marks on it in measured increments, and a piece of chalk in about 15 mins by myself or even quicker with a helper to stand on the block of wood and ensure it doesn't move. Someone else might take 30 mins if they have never done it before, and they may do it a bit wrong - which is why it would be nice to have a autonomous process that can handle this trivial task that needs to be done at least 2-3 times a week at various locations.