Archives for posts tagged ‘FDM’

clip-on mustaches for Crushtoberfest ’12

It’s Crushtoberfest time again… time for mustache-related tomfoolery leading up to our big, hairy keg party. With all the men-folk growing their best mustaches (open to any facial hair this year, BTW), the ladies inevitably feel left out, so this year I wanted to help get them involved.

Sadly enough this was one of the more challenging 3D modeling projects I’ve had recently. I first sketched a couple of splines to define the general shape of a mustache, then created an ellipse perpendicular to those curves. I then projected the splines onto a curved surface so the mustache would better follow the shape of the face, and swept the ellipse along them.

I then mirrored the ‘stache and cut out an additional scoop in the back to make room for the clip. The clip was designed to fit into the nose and clamp the part in between the nostrils. I took a blind stab at the sizing of all the elements, hoping it would be  flexible enough to be comfortable but stiff enough to not fall out. I printed one out and tried it on… Turns out the spheres up top were not big enough and the clip was way too stiff, resulting in immediate pain, especially when removing it.

In the revised design I added some loops in the clip to make it more compliant, made the pads bigger and flatter, and added some fingernail nubbins to help spread the pads to put the mustache on.

I took this one around to some test subjects and we determined the mustache was a little too wide and thick to allow for beer drinking, so the next revision shrunk everything down a little.

The geometry of the clip changed enough to affect the compliance, but we’re still within acceptable stiffness. The best part is the layer lines inherent in the FDM process makes for a near-perfect mustache-hair texture. Here’s the finished product, ready for Crushtoberfest!

UPDATE: I uploaded the .stl files to Thingiverse!

UPDATE 10/25: Here’s an alternate style, for those of you into the push broom. Also available on Thingiverse:

bouncy-ball race trophies

That’s right, bouncy-ball races. Crushtoberfest is about three things: mustaches, drinking, and a complicated competition that makes adults look ridiculous. This year we had a couple of great ideas–like mini-bike jousting–but one too many conversations about safety killed that one:

Lack of time was also a factor this year, so compromises were made and we ended up here:

Since there’s really no “making” in the event, I looked to create a fun trophy instead.

A combination of FDM 3D-printed parts, laser-etched name plates, stained oak and lots of gold spray paint resulted in a surprisingly “official” looking trophy.

3D-printed shop vac adapter

Believe it or not, 3D printing can be used for more useful things than clip-on mustaches… I have a miter saw with a missing dust bag, so whenever I use it I fill the immediate area with a fine coating of sawdust. I always thought a shop vac attachment would be more useful than the bag anyway, so I bought a 1.5″ to 2.5″ adapter that didn’t work at all. So I simply measured both ports and sketched up a quick elbow adapter.

I then modeled it in CAD, converting inches to mm and fine-tuning some of the dimensions and details.

A couple of simple sweeps and shell features, plus some details for hose clamps (a backup, in case the friction-fit doesn’t work):

The print took about 8 hours and required copious support material (which in turn took copious cleanup) but it came out perfect.

And fit perfectly too (no hose clamps required)!

I’ve uploaded the part to Thingiverse… enjoy!

vacuum pump muffler

I recently bought a small vacuum pump for a project (I will get into that at a later date) and found it to be surprisingly noisy. At first I thought the noise was emanating from the housing itself, but when I blocked the outlet port with a finger the noise was cut down dramatically. A colleague suggested a muffler (thanks Keith!) and another gave me some tips on how they work (thanks Andy!) so I set out to make one.

It turns out there are several strategies for muffler design, and some of them get complicated, acoustically speaking. Most engine mufflers are optimized for unrestricted air flow, as air resistance saps horsepower. In my case the air flow is relatively low and I’m not concerned about a fractional drop in suction, so I went with a simple maze-like muffler design, intended to disperse and diminish sound pressure as the waves travel through the maze.

muffler

 

I printed the parts on the FDM machine…

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then glued the two halves together. Is there anything Loctite can’t do?

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The inlet port is sized for my 1/4″ ID hose, although in a future iteration I would add a barb feature to make the attachment a little more positive. For now I’ll just use a small hose clamp.

I measured the sound level (from 18″ away) at about 93 dB without the muffler, then about 82 dB with it. Hear for yourself:

 


My First Robot part 2 – 3d-printed tank treads

I found it surprisingly difficult to find just the right small-scale tank treads I wanted for Isabell’s robot, so naturally I looked into brewing-my-own. I first went down the RTV silicone path, but soon reeled it back to reality… I want to get this off the ground soon, then maybe look into full custom treads for the next generation. So the following is an experiment, sort of a feasibility test for 3D-printed tank treads.

rover_treads_2

 

This is really my first pass at a “tooth” design in CAD, based on nothing really. The cog teeth are simply arc sections meant to make the lead-in and lead-out smooth, and the tread profile is a rough approximation of the cog teeth.

rover_treads_1

 

This is the result, using an FDM tread on a laser-cut acrylic wheel assembly. I actually made three different sized sets of wheels and picked the best fit, then measured and cut the rectangular parts to provide a decent pre-load on the tread. The whole thing is held together precariously with a couple of dowel pins (and comes apart quite easily).

I had some concerns and they were mostly justified… The tread slips off the wheels easily after playing with the assembly for a couple of minutes, but that could be fixed with some retaining features. Also I suspected the tread would take a ‘set’ after sitting still for a couple of days– a function of the creep properties of ABS. Sure enough, a few days later I took the tread off and it had an elliptical shape, which I could feel in the form of on-again-off-again resistance when rolling the assembly along. I’ll bet a thinner-walled tread would be less prone to taking a set but still be strong enough to survive all the deformation. Ultimately I think the idea is feasible, but an RTV-cast silicone part would be my first choice for many reasons.

 

My First Robot part 3 – Drivetrain

Once I decided a custom tank tread wasn’t going to work for me, I went back to searching the internet for an off-the-shelf solution. Someone recommended looking at Lego Technic parts, and sure enough I found this on Ebay (EDIT: a helpful commenter on hackaday pointed out this much cheaper option). I don’t know what set this came from, but they are just about the right size (a little on the small side, maybe) and the price was right. Once they arrived I got them into CAD and quickly pulled together a basic design.

rover_CAD_1

 

Aside from the treads this design is driven entirely by a few key components. First are two small SM-S4303R servos, which offer continuous rotation without modification. After much debate I decided on this lithium ion battery pack from Adafruit for two reasons: it has 6600mAh capacity which should provide hours of use between charging, and it is known to work well with this multi-source charger, also from Adafruit. I have plans to include solar charging in the future, which will impose some challenges, but I’ll get into that later.

tractor_exploded

2014-04-12 13.08.02 The rear tank tread wheel is mounted to a sliding part that allows the tread to be tensioned just right. The front wheels are attached directly to the servos, via a modified servo horn that I turned down to size on the lathe and glued into the wheel. Shown below (from left to right) is the original servo horn, the same part after turning its diameter down, and the wheel it is about to be glued into.

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Once glued together, the screw that holds the wheel onto the servo is trapped in the assembly:

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The chassis is 3D-printed, and I used small brass threaded inserts everywhere, considering how much I expect to be disassembling/reconfiguring things…

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…which made assembly nice and smooth.

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The top part is a slab of polycarbonate, meant to be easily removed and re-drilled, etc. as things change and evolve. Here it is, ready for electronics!

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