This is a small ball caster to be used on robots or other things that need to roll.

The openscad file is set up to easily tweak values for commonly changed parameters:

Ball Diameter
Airgap - How much play between the ball and the wall
Ball protrusion - How much the ball should stick out of the housing.
Total Height.
Base thickness.
Mounting screw radius.
Spread between the mounting screws.

I've started playing with a parameter to switch between two different mounting types. This isn't done yet which is why the part is marked as a work-in-progress.

Ears will create a part as shown in the picture. Meant to be mounted with two external screws.

Center Screw would have a counter sunk screw in the center of the main cylinder. The caster could then be screwed in before the ball is snapped into place.

My reprap isn't particularly well tuned but the ball spins freely.

I'm incorporating this design directly into scout. thingiverse.com/thing:13042

Scout is a printable tribot designed for teaching the Boy Scout robotics merit badge. scouting.org/scoutsource/BoyScouts/AdvancementandAwards/MeritBadges/mb-ROBO.aspx

I've marked this as a derivative of MiniSkyBot because I was inspired by it and because Scout still uses the wheels from that project.

The frame itself is a complete redesign with similar but different goals.

Goals:
Provide a kit that meets the merit badge requirements with parts totaling < $50 USD.

-Minimum printed parts
-Minimum vitamins
-Accommodate an arduino diecimila or nano.
-use a 9V battery.
-Flexible enough to allow boys to improve and extend the design.

The frame is a single printed piece. The tabs for holding the servo motors can be tapped with a 4mm tap to avoid the need for nuts.

The top holes can be tapped with a 3mm tap to screw on an arduino without nuts.

The bracket will hold a 9v battery with just friction. The rear battery bracket has a friction fit cup for a ball bearing caster.

Large holes in the bracket minimize the amount of plastic needed and allow wires to be routed up to the arduino.

Cost
Since affordability was a major consideration, here's a run down of the final project cost.

The plastic cost is just the cost of a roll divided by the number of kits we built. There was lots of plastic left over and the boys are using it to design improvements.

Frame & Wheels $7.86 (plastic from Makerbot)
Tires (2) $2.36 (Hardware store o-rings)
4mm bolts (4) $0.84
wheels screws (4) $0.96
Servos futaba (2) $8.38 (purchased new in bulk on ebay)
Arduino Nano $18.99 (purchased new on ebay)
Ultrasonic $3.90 (purchased new on ebay)
9v connector $0.81 (Radio Shack)
DC power plug $1.86 (Radio Shack)
9V battery $1.25
Total: $47.21

This started out as a project to learn modeling in FreeCAD. I've attached the FreeCAD project file as well as the .stl models.

I'm not sure what I'll do with it, but it seems like it would work nicely in some kind of Halloween costume.

The main bracket works like a clip-on spray-paint trigger -- In fact, the bracket should fit other kinds of rattle cans as well.

The servo bracket was modeled to fit a hobby servo I had lying around. I've found that servos have a variety of different mounting screw patterns so you might have to modify this for whatever servo you're using.

A bent bit of paperclip works to connect the servo horn to the end of the trigger.

Here's a short clip of it firing: youtube.com/watch?v=fPpnoXX5sNc

After trying a resistor heated hot-end, I got a little concerned with the tight fit in the standard mendel X axis carriage. I tried Bubak's OpenX Carriage (http://www.thingiverse.com/thing:6278) and I really like having an open center.

In my config, I've got the dump zone on the far left and the OpenX won't let my extruder reach it. I started playing with this idea for a very lightweight carriage that would only have what I needed. Since I use mechanical endstops, it has no holes for mounting flags and is optimized for a horizontally mounted Wade's extruder.

This design is narrow, light, and uses only 8 bearings. (It might be possible to fully constrain it with just 6 bearings by eliminating one on the bottom of each rail.)

Since this is just an experiment, I'm marking it as a work-in-progress and I welcome comments.

So far, I've only printed a couple small parts with it but it seems very light and tight.

carriage3.stl is a revised version to deal with a couple problems:

The belt is uncomfortably close to the screw heads on the unclamped rail. In my setup, it barely touches, but any rubbing is probably too much. This version recesses 4mm nuts in the carriage and expects a 4mm bolt instead of socket head cap screw. The direction of the bolts is reversed.

The posts for mounting the extruder have been widened and are a little taller to give some additional clearance for the big Wade's gear.

I added a gusseted side on each end to stiffen the carriage.

I'm still planning to redesign the clamping rail to add a tensioning screw for the belt.

A minor change to add a bore to the center of the foot. This can be tapped to allow screwing in a bolt as an adjustable foot.

This is a replacement clamp for the Y-axis drive belt. It allows the belt tension to be fine tuned without removing the bed.

One end of the belt is clamped to the Y chassis "squashed frog" with the standard clamp. After threading the belt around the motor and pulleys, the other end passes under the gap in the new clamp, loops back over the top of the clamp and is held down with the cap. The whole thing is held the carriage with 2 3mm cap screws and nylocks just like the old bracket. The ram is placed into the loop where the belt doubles back. A 4mm cap screw goes through the back of the clamp and pushes the ram forward. By turning the cap screw, you can change the tension on the belt.

This design might work just fine without the ram and be a little easier to assemble. I haven't tried it.

This is a clip-on bracket to mount a RAMPS board on top of a sells mendel. It clips on over the top of the Z-axis leadscrew so it won't work on a prusa. It uses the same clip dimensions as My Fan Bracket (http://www.thingiverse.com/thing:8329)

I decided to mount my RAMPS board on top of my sells Mendel. (http://www.thingiverse.com/thing:8330). I had a 50mm fan laying around and designed this bracket to hold it blowing on the stepper drivers.

It's designed to hold itself in position with just friction and snaps on and off easily. I'm using the same snap design to hold the RAMPS bracket.

This is an openSCAD version of thingiverse.com/thing:5450

Note: My car was featured in the September 2011 issue of Popular Mechanics
popularmechanics.com/home/how-to-plans/backyard-genius-2011-the-years-10-best-diy-creations-jet-propelled-pine-wood-derby-car

This is a 3D printable motor for an 'outlaw' class Pinewood derby car. My son's cub scout pack has run an outlaw class for the last couple years. I've made other cars (http://sliptonic.com/?p=113) but this year I wanted to make as much as possible 'printable'. The trigger was inspired by a medieval crossbow mechanism. I welcome comments on improving it.

youtube.com/watch?v=8d4W5kBPek8

First a note: My name for this car was 'Bad Idea' and it probably is. It's completely illegal in regular pinewood derbies, possibly dangerous, and will certainly scare every mother in the room. You've been warned. If you decide to build one, please take extra safety precautions like the note mentioned below and maybe make everyone wear safety glasses.

The motor uses the following printed parts:

Tankblock: holds 2 12-gram C02 cartridges at a downward angle. A channel between and below the cartridges lets a stiff wire pass underneath from the front bumper to activate the trigger mechanism.

Trigger block: Holds the parts of the trigger mechanism is alignment.

Pawl: The pawl is pushed toward the back of the car when sitting at the starting gate. It rotates on a common axle with the hammer and keeps the sear from rotating.

Sear: The sear grabs the hammer and releases it when pressure is removed from the pawl.

Hammer: Pulled forward by springs, the hammer does the work of piercing the cylinders. The hammer has a large cylindrical opening to be loaded with weight. A brass rod rests in a groove in the hammer and connects the springs. As the pins pierce the cylinders, the rod pulls out of the groove. This lets the hammer fall back and clear the way for the gas to escape.

I'm using a pololu and carrier to drive the extruder on my mendel. I didn't have a good place to mount it so I made this little bracket to mount it over the extruder board.

It leaves enough room for good air flow and to reach the ttl header, reset switch and to turn the screws on any of the other terminals.

Know a Jack-o-lantern that needs his guts ripped out? Tired of tools that just don't get the job done? Maybe you just want to inflict some Halloween mayhem on an unsuspecting pumpkin. Here's the tool for you.

An ergonomic palm-sized tool perfect for gutting your favorite gourd.

It's time to get medieval...and slimy.

This is a little bracket for holding my walkman in my truck. It's sized for a Sony Walkman NWZ-E436F.

It doesn't have a mounting hole included but drilled and countersunk a #10 screw through the middle of the back and screwed it to a lighter plug thing.

A two-part thing for mounting something in the cigarette lighter of your car.

The bottom of each section has a hole to accommodate a #10 screw.

This could really be improved by recessing the bolts into the convex parts of the top.

This is a pencil box I made for my son. It's designed to hang in the corner of a locker. The recesses accommodate magnets like these: amazon.com/Earth-Neodymium-Magnets-Pieces-Applied/dp/B0012AUU84/ref=pd_sim_hi_4