Category: Blog

The State Of The Chipi

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.

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.

ChipiKart In which I Dont Play With Motors

The title says it. Time to build.

A quick steel run and some time with the chop saw later, this happened.

Thats most of the base of the frame. When making a frame like this, the trick is to break it down into individual units of two pieces, weld the units square, and then weld the units together. That way, the whole frame stays strong and square. So! Welding!

Back frame reinforcements, cooling down.

Then the rest of the base gets welded up.

And the reinforcing brackets are welded into place.

I cut some more parts for the foot bar and the seat mounts, and welded them up.

They were then added to the frame. Since I dont have a seat yet, Im going to hold off on the seat mounts, as I need to measure whatever seat I end up using so that it will fit on the brackets.

And thats most of the frame done. Now I just need to do the drives, steering, brakes.. and pretty much everything except the bare frame.

 

Well, ChipiKart is done(ish). It raced at the San Mateo Maker Faire, but thats another story.

One thing Ive been meaning to do to ChipiKart is replace the lead-acid batteries with something better, like one of the more stable lithium technologies. Those are expensive, though. But at the maker faire, I was able to pick up some pretty neat surplus.

This is a A123 module. Its 16.4v, 2.5 Ah. But thats not the fun bit. The fun bit (aside from the super-flat discharge curve) is the (reported) maximum discharge of 200A, which is rather a lot of amps. It will also take somewhere in the vicinity of 60A charge current, which is just silly. I cant find a datasheet to verify those numbers, but I wont be approaching them so I should be safe.

I was able to purchase four units, so I planned on making two quick-change packs. Making quick-change packs means I get to do one of my favorite things: make boxes. So I grabbed some sintra (expanded PVC foam), and headed off to the table saw.

This was the first box. It holds one pack.

An identical one gets stacked on top. Notice how the middle divider isnt solid. This will allow me to get some airflow over the batteries, and maybe insert a temperature probe. I doubt Ill need it, though.

The packs slide in like this.

I added some reinforcement, and hit it with a router to make it look presentable.

I dont have any appropriate wire, so I made copper bus bars to connect the modules in the pack.

The whole thing goes together like this. I still need to cut a keyway in one side and key the receiver so that its impossible to insert the batteries backwards. Lots of amps backwards is bad.

But now I have a scary-pack! It weighs 4.4 lbs, as compared to my lead-acid pack, which weighed 18.2 lbs. Now thats an improvement.

Coming up, a receiver, charger, and the rest of the battery system.

An Aside Making Counterbores

 

Today, I wanted to do some single-point thread cutting on the lathe. But when I went to set the compound, I noticed this.

 

My tool post was butting up against the edge of the compound, and so I couldnt rotate it to set it straight. Actually, When I first got the tool post, it didnt fit at all. I had to mill a bit away so it would sit flat. I didnt think to mill away enough to be able to turn the post. Derp.

 

So I stripped off the compound, popped it in the mill, and began cutting. The section I cut is about 0.0005 low, so the tool post will sit flat.

 

Plenty of room now!

A Carriage Stop For The Lathe

I havent been completely idle on builds like TinyMill.

Ive just needed more tools.

One thing Ive 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 Im going to build one, because Im crazy. Ill be following another one of Deans builds.

One thing that I considered in my decision to build this was cost. And because I dont 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 theyll ease the process of cutting this monster.

And now, if youll excuse me, I have a date with a bench vise and a hacksaw.

Building A Boring Head

 

And so it begins.

 

I cut off a couple 1.25 lengths of the cast iron bar, and faced the ends to make them pretty. The big thing about this cast iron bar is that it isnt round. So although the ends of the bar are flat now, they arent necessarily perpendicular to the length, or even parallel with each other.

 

I popped one in the 4-jaw chuck, and faced the end again. I now have an end thats flat and straight as long as its in the same setup. I then turned down a section to 1.395, as called for in the prints.  That section is now actually round and perpendicular to the faced end. This end of the workpiece is now a datum, a reference that I know and can work off of for my next operations.

 

This end of the stock gets threaded 3/4 16. So I started by drilling out to the largest diameter I have, which is 1/2.

 

And I then bored it out to 0.7031, which is the required diameter for putting in 3/4 16 threads. Since the bore was done in the same setup as the facing and turning, the bore is concentric with the outside diameter.

And now I face a conundrum. I dont have a 3/4 16 tap. And I dont have an internal threading tool. I have some broken cutters I could grind into one, but theyre all carbide, which my aluminum oxide grinding wheel just cant handle. So Im stalled until either I buy one or think up how to make one. Stay tuned.

TinyMill Part 6

Over the course of designing some more parts for TinyMill, I realized that I needed to counterbore some holes. I could easily fake it with an end mill or drill bit, but one of my design goals was to not have any kludges. I could buy a counterbore, but thats $30 for a set that I might use one of every (not) so often. Or I could buy some drill rod and make my own. Guess which option I chose.

Before I start, I need to give credit where its due. I first learned that I could make counterbores on the HMEM forums, and then learned how to from Deans excellent page. Seriously. Dean did a really good job of walking through how to make a counterbore. So Im not going to make a tutorial. These are just a few selected photos of the process, and some notes. So lets begin.

 

This is a length of 3/8 O-1 Drill rod. A 36 length cost me about $3 (shipped!) from Enco. Its about 5 long. The counterbore Im making is for a M4 SHCS, so it has to be turned down to 8.25mm.

 

A sharp carbide cutter works wonders on tool steel. I got to about 0.0005 over my final diameter, then brought it down with some 220 and 600 grit sandpaper (with oil) on a parallel to keep everything nice and flat.

 

Repeat that for the pilot and you have a nice cutter blank.

 

Lacking any method of indexing, I had to make a fixture for cutting the flutes. It would have been nice to use a piece of hex stock (to get a 6-flute cutter), but I didnt have any. So a piece of 7/8 square 12L14 was pressed into service. It was drilled for the cutter, and had a set screw added in the top.

I didnt take any pictures of milling the flutes. Thats a lie. The milling fixture was just so in the way of the light that none of them were any good at all.

On Deans page, he mills the reliefs for the ends of the flutes. I had just indicated my vise in square, and didnt really feel like canting it off at an angle, so I did all the reliefs (very, very carefully) with a fine file. It worked well.

 

A final shot, of the heat treating. It went fairly well, although pure propane lacks a bit in the heat department and my flame was a bit on the small side of what I would have liked. A quench in motor oil and then a quick tempering brought the hardness to somewhere around 50 rockwell. Plenty good.

So now I know how to make  counterbores. Its pretty good, and I have to make a couple more, but now Im a bit addicted. Uh-oh.

Inspiration

A while ago I found out about Evil Mad Scientist Labs 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 Im too lazy to do anything else.

 

The initial plunge. Im 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 dont have to hold it myself.

 

Engraving the inner ring.

 

Cutting out the final shape.

 

The finished coaster. Its 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.

Thats really it for coasters, as I make more designs Ill put up more photos.