Introducing The Odd-End

I’ve been printing a lot lately with a couple of extruders. On my ORD bot, I use a MakerBot MK7, and on my cupcake, I use a MakerGear stepper plastruder. And what I’ve come to realize is that I don’t really like either of them. Or rather, I really like some elements of each, but not really the whole package for either.

The MK7 is very compact, and I really like that, especially for a smaller printer like the ORD bot. And the hot-end is uniquely short. It is about 20mm shorter than the MakerGear. That being said, the drive sucks. The filament “idler” is a piece of delrin that is held pressed into the filament using not a spring, but the flex of the drive housing. There’s a lot of stress there, and no adjustment. It is also driven directly off of a NEMA 17 stepper motor. That would be great if it needed to turn at high speeds, and it does mean thet there’s no gearbox to take up space. But it doesn’t turn at high speeds, and to get the needed torque It sucks down about 1.6A. That means the motor gets really toasty (so there’s a heat sink to cool it, which takes up space), and the driver gets so hot that I have to fan-cool it or it goes into thermal shutdown. Not good.

The MakerGear, on the other hand, uses a geared stepper. It has awesome torque, even with the driver turned almost all the way down (so the driver and motor are always cool to the touch). The only problem is that the gearbox takes up a lot of space and weight. But the filament drive uses a proper ball bearing driven by springs, and the drive gear is accessible so you can clean it without dismantling the extruder. My only real kvetch is that the hot-end is long (and unlike the MK7, not all-metal).

So I have two extruders, and in the end, I don’t really like either of them. Frankly, I can’t find one I really do like, but that’s just because I’m very picky. But I have tools, so I’m not allowed to complain. I need to design my own extruder. I started with the hot-end. I wanted something like the MK7, but lower friction. The MK7 has a relatively high-friction thermal barrier, which is also made of the somewhat thermally conductive stainless steel. I don’t plan on extruding any crazy polymers (such as ploycarbonate… yet), so I shouldn’t ever need to go above 280ºC. This means that I can use a plastic thermal barrier. Stainless is alright (an order of magnitude less conductivity than brass), but something like PTFE or PEEK (an order of magnitude less than stainless) is even better. PTFE also has crazy low friction. But it’s not strong, so I can take a page from MakerGear and make a hybrid insulator. I came up with a PEEK shell and a PTFE liner. The PEEK provides structure, and the PTFE provides low friction.

The heater block was fairly simple. I took a block, and added a threaded hole for attaching the nozzle and thermal barrier. I used a power resistor for a heating element, since they’re cheap and easily available. And just for kicks, I threw in a divot to stick a thermistor in. I spent a while trying to decide if I wanted a thermocouple or a thermistor. Thermocouples are good to 1600ºC (not necessary) and need no calibration (nice). But they’re incredibly noise sensitive.  have one on the MK7 extruder, and even with tons of filtering can’t get all the noise off the signal. So I decided on a thermistor, which is pretty much noise-proof (nice), and cheap (even better).

And so the last component is the nozzle. I have no engineering background, and so I don’t really have any way to quantify the design of something like a nozzle. So I went on intuition and drew out something that just looked right. But now enough blathering, it’s time to make this beast.

Here’s how the thermal barrier came out. I single-point cut the M8 threads on the lathe because I didn’t have a die, drilled it out to 4mm, and slipped in a bit of PTFE tubing. That was pretty easy.

The heater block was another easy one. It has two holes, and was a nice quick job on the mill.

This was the hard one. I turned the nozzle out of hex bar. The threads were cut on the lathe again, but the nozzle hole was drilled on the mill. I just can’t make the lathe go fast enough to use a 0.4mm bit.

And here it is assembled, with a US penny for scale. I assembled it, cemented in a resistor, and fired it up. I don’t have a drive for it yet, so I just pushed filament through by hand. It went through easily, so that’s a success. And it came out 22mm shorter than a MakerGear hot-end, so that’s a success. I guess now I have to build a drive for it and really put it through it’s paces. Or make a bunch more. Or both.

Building The Darn Thing Part 5 of n

 

Maker Faire San Mateo is quickly approaching, and with it the first event of the 2013 Power Racing Series. Which means that ChipiKart is going to have to be much more than a gravity-powered death trap, and fast. With this deadline in mind, Ive been plowing ahead, and am pleased to present this thing.

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Its most of a ChipiKart. With some changes. The original steering wheel was made of 3/8 thick acrylic, which is brittle enough as is, and really didnt last long in the sub-zero temperatures I tested it in. In the absence of a suitable replacement, I used two vise-grips as a replacement. It works, so stop judging me. It also has one drive motor hooked up, so it moves under power. Theres still no brakes.

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Heres my motor unit. Its the SK3 6364 motor from last time, but mounted to a bodged-up mount. Theres also a 3D printed bracket holding some sensors.

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The sensor board (courtesy of Big Chucks Robot Warehouse) is mounted to the motor with a 3D printed ring. The sensors provide a position reference for the controllers so that the motors can commutate properly in a zero-RPM condition. This means that I can start from a stop, or a stall. Handy.

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And heres the controller Im using. Its a generic shady Chinese controller, with some modifications. Ive replaced the no-name FETs with nice IR FETs that will dissipate less heat, and Ive upped the current limit from 10A to somewhere above 60A. Well see how that goes.

 

Heres the inside of the controller, just for the curious. If you want a good tear-down, look no further that Charless excellent report.

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Moving on, putting motors on the Kart. I was planning on bolting the motor mount to the frame so I can adjust it, so I put on a few tacks with the MIG welder to hold it in place while I drilled it. I ended up liking the way it was aligned, so I ditched the bolts and just welded it.

 

Because I dont want everything on ChipiKart to eb a complete hack, I decided to make the controllers look nice. I hacked off a hunk of aluminum box extrusion and made a nice enclosure which I will name ChibiTroller. It houses a 300A cutoff switch, proper anderson power connectors, two Jasontrollers, a cooling fan, and some arduino telemetry stuff that I dont really understand. The goal is to be able to report back to pit lane in real time various different sensor readings. I havent installed any sensors yet, nor have I decided what I want.

Building The Darn Thing Part 5 of n

Well, I went through a quick blitz of making things, then kind of dead-ended. By which I mean I ran out of parts and had to stop work. But heres what I got done.

Steering:

I built the steering column! And made a steering wheel! And didnt take any pictures, but heres some video of what it looks like laser-cutting 3/8 acrylic on a 30W CO2 laser.

 

And then I had a rolling chassis, and wanted to drive but had no power. So I decided it was time to soap-box derby this thing.

 

No, I didnt crash at the end. But I did break the steering wheel in half. I dont know what I was expecting; it was about ten below zero outside.

It was at this point that I realized that I had nothing else to do but put motors and brakes on it. And I didnt have motors yet, so I stopped short.

Until today, when I got a box from Hong Kong.

 

Motors and a battery charger! But lets focus on the fun bit of that.

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The motors are Turnigy SK3 6364. I love these things. Theyre actually well built. The magnets are glued in, the stators are pinned, the windings are tidy(ish), and they have can bearings! This one also has a fairly low kV (180), and 2400 Chinese watts of power. Oh yeah. Now that I have them, I can model them, put them in the ChipiKart CAD file, and design some motor mounts. Other projects can wait, Ive got motors to put on things.

Asymmetry

On The Small(er) Scale

Mini sumo is something I’ve been interested in for a long time. The basic premise is simple: two robots are in a ring, and have to push each other out without falling out. There are a lot of rules, which are detailed here, but only a few really matter to me. I’m not going to try to make my robot fly, after all.

The two critical requirements (mechanically, at least) are that the robot must be no bigger that 10cm x 10 cm and weigh no more than 500g. So I have to work small.

Updates as I work. This is a build log, after all.

The Design In Brief

I designed Asymmetry in QCAD to fit within the size and weight limits of the competition. Yo can download the mechanical design files here.

It uses a sliced design, with the interior being made of plates of 6mm Sintra. There are ten pieces: three center braces, a left brace, a right brace, a tongue, a left side plate, a right side plate, a front plate, and a top plate. All of the pieces except the front and top plates will be cut on my CNC machine.

 

For motors, I’m using faulhaber gearmotors with the right angle box removed. They’re bigger than I would like, but they’re what I had laying around.

 

For wheels, I used these awesome wheels from solarbotics.They have great grip, and…

 

They fit perfectly on my motors.

As for electronics, I’m not sure yet how that will play out.

 Center Braces

I got the center braces cut today.

 

They all came out well, although the cutter ran into the middle one when it popped out of the material. Other than that, they’re all alike, to a 0.005″ tolerance. Not shabby.

 

The motors are a slip fit into the holes. They’re not aligned with each other, which doesn’t effect performance. Well, the robot can’t tilt forwards or backwards, so I guess I just have to keep it upright.

Starting to see why it’s called Asymmetry?

Completing The Undercarraige

Today I cut out the rest of the undercarriage. So I have a gratuitous picture of the CNC machine cutting the left brace.

These are the rest of the pieces. From top to bottom: left brace, right brace, and the tongue.

The braces are a press fit on the tongue.

With the center braces added, we have a complete undercarriage. Click on the above picture for more. Everything is out of alignment, but I’ll make sure it’s perfect before I glue it.

Next up, the side plates, front plate, and top plate!

Side Panels

I cut the side panels today. Not much to ‘em.

The side panels attach to the inside braces, which press fit onto the tongue. I didn’t want to glue on the panels yet, so I attached them with very strong double-stick tape.

With the side panels on, you can get a feel for the shape and size of the robot. All it’s missing now are the front and top panels.

 Front And Top Panels, Brains

Starting off with a sidenote, I got the side panels glued to the side braces. The white around the edges is residue I’m too lazy to sand off.

Back to the topic, I got the top and front panels cut.

When assembled, it looks like a little black box. It is a little black box. With wheels. Note that there are no holes in the front and side panels for the sensors yet. Also note that nothing except the undercarriage is glued in place.

The inside of the robot is pretty spacious. I have 3x3x1.2 inches of space. I’m curious to see how much battery I can fit in there.

This is my protoboard so far. The power supply is in the upper left corner. Right below it is the H-Bridge motor driver. In the middle is the ATMEGA328P. It’s pretty messy, and is going to get a whole lot messier when I add the opponent sensors. I think I’ll eventualy mill a PCB with all SMD components, but knowing me this will probably be the final board.

The two ribbon cables coming off the top are the front floor sensors.

These are what I’m using for floor sensors. They’re small IR reflectors, and have a range of about 4mm. They give a very clean difference between the black of the arena and the white border. I have two in the front now, but may add more in the back.

 Sensory Overload

I got the edge sensors glued on to the frame. It’s not too pretty, but it functions well and no one is going to see it. I hope not, anyway.

This also means that the board is permanently attached to the robot. I guess I’m not going to make a routed PCB. Probably.

The front and side panels now have proximity sensors. They each have a range of about 50cm, which should be good enough.

There’s a rat’s nest of wires on the back of each of the panels. This is going to be a nightmare to solder, especially considering that due to the design of the robot, I have to glue on the sides before I can solder the sensors to the board. Oh boy. We’ll see how that turns out.

Back From The Dead

Prior to my previous thoughts, I turns out that I actually didn’t fry the whole mainboard. I needed a cool demo for my school’s tech club, and so I pulled out Asymmetry and started debugging. It turns out that the motor driver circuitry and some of the power supply was dead, so it was a quick fix to get it back up and running. Every last sensor works, so I put in some code and set it off traipsing around our table at a activities fair. It got a fair bit of attention, which was cool. Soon (yeah, right) I’ll get some actual code written and do some trials. Until then, it will go back to sitting on the shelf staring at me.

Making Coasters

Inspiration

A while ago I found out about Evil Mad Scientist Lab’s font coasters. I thought it would be lots of fun to make my own, and so I began scanning for fonts and material. I decided that Times New Roman was too drab, and settled on something more exciting — Webdings. I had been putting this project off until I found a roll of cork in the basement, and then I had no excuse. What follows is an attempt at documenting the process of making a font coaster on a CNC router.

The Photos

Here are the photos. The coaster is a ) (right-parenthesis) in Wingdings.

This is how it looks in EMC.

The machine over a piece of 1/4″ cork. I just tacked it down with blue tape, because I’m too lazy to do anything else.

The initial plunge. I’m using a 1/8″ end mill from Drill Bit City.

Cork cuts like a dream. Smooth edges, and I can cut pretty deep. I was using depth passes of 0.08″, but really could have done 0.12″ (or deeper) if I wanted.

The dust is pretty fine and hard to clean up, so a vacuum is a must. I really need to make a vacuum mount so I don’t have to hold it myself.

Engraving the inner ring.

Cutting out the final shape.

The finished coaster. It’s about 3.25″ in diameter. I accidentally cut the inner ring 10 times deeper than I meant to. It should be 0.014″ deep instead of 0.14″ deep, but at least it shows up well in this photo.

That’s really it for coasters, as I make more designs I’ll put up more photos.

Building A Boring Head

A Carriage Stop For The Lathe

I haven’t been completely idle on builds like TinyMill.I’ve just needed more tools.One thing I’ve been wanting for quite some time is a boring head for my mill. And when I was re-designing the x-y stage for TinyMill, I realized that I actually needed one. So I’m going to build one, because I’m crazy. I’ll be following another one of Dean’s builds.

One thing that I considered in my decision to build this was cost. And because I don’t just happen to have large diameter pieces of steel lying around, that could be pretty high. And then, when looking at metals, I noticed that for some reason, fine grain cast iron was cheaper than steel. And after a lengthy discussion on the HMEM forums, I reached the conclusion that cast iron would be alright.

So this is where I am now.

I have a 1 foot length of 1 3/4″ cast iron, and some new hacksaw blades. Hopefully they’ll ease the process of cutting this monster.

And now, if you’ll excuse me, I have a date with a bench vise and a hacksaw