Snuffles Reloaded: Update ∫f(t)e^(iωt)dt

chorl2 Comments

Oh man, it’s ALMOST THERE! Spring break was too short, or else I partied too much at the Media Lab. Either way, OH MAN, IT’S ALMOST THERE! Build pics from the past few days…

So, to make the motor endcaps, I had to perform some slightly odd machining. The endcaps are dish-shaped, which would have been simple had there not been a lump in the middle to house the axle bearings. In order to make this lump in a dish, I needed to plunge cut into the face of the dish by about 2 millimeters.

This was a simple enough task when I had access to an awesome shop full of precise machinery and tooling out the nose, since some careful boring bar work took care of it the first time.

Unfortunately, I only had my not-boring-bar. Despite my best attempts at grinding the proper angles to let it plunge cut, and trying to align the toolpost to my best ability, it still sucked ass. I decided to wait until the building was vacated to keep working, since although the tool did cut, it made a 9000+ decibel high-pitched squealing despite all attempts to quell it. So there’s a very good reason I waited until 4AM to finish these things…

And so above is a picture of the First Attempt. All I had to do was make a trench big enough to stick a real tool in, or use the Not Boring Bar like how it’s supposed to be used (which is how…?). The outside is decent, but as you can see, the inside surface is horrific.

A quick run-through with a pointy tool solved the problem, however. It turns (hehe) out I cut a bit shallow, but fortunately, the custom-ground HSS bit could face cut a few hundredths and clean the inside corners to boot.

Flipping the thing around to bore the bearing cavity. As usual, it was ghettocentered with additional assistance from a stack of milling parallels jammed between it and the chuck. This insured the stator against being completely off-axis from the can and blowing things up like it did on the previous wheelmotor’s first build attempt.

Done. This is what I call a “Loctite finish”, which is when the finish is so smooth and accurate that whatever is being mounted slips in with a modest push of the thumb. With some green Loctite (I prefer 609 ultra-thin retaining compound) in the mix, the part will never come off again.

Ever.

(BTW, I lost the above image twice due to WordPress’ curious habit of making “undo” remove everything you’ve done for the past 5 minutes….)

And so with lessons learned from the first part, the second part was much, much smoother. I ground one of the 60 degree threading tools with a rake and side clearance angles so it could take the plunge smoothly. The procedure was to plunge cut, then move the tool in and out radially, making a wide slope-sided trench, feeding in more with each pass. When the sloped sided trench had been cut to the proper depth, the not-boring-bar was used to square off the corners.

The last step was to trim the diameters and cut the odd taper to mate with the scooter wheel. The diameter downsizing was smooth, the taper was not. There’s one downside to machining on low sleep reserve – you also have low common sense reserve. It would have been greatly smoother if I had set the compound slide at an angle and fed it in and out, like how you’re supposed to cut short tapers.

But instead I angled the tool itself and brute-forced it. Chattery results clearly shown. The dimensions and such are acceptable, but the finish is total bullshit. I slid some sandpaper over it to try and redeem myself, but decided it wasn’t worth the effort.

It’s on the inside of the wheel anyway….

Hey, it’s the 100th build picture of Reloaded! I have a habit now of documenting every little process involved with my projects. This is good, I suppose. Too bad the 100th picture can’t be of a finished product.

Instead, it’s of the magnet can. There will be 14 magnet poles (7 pairs), each of which is composed of either 2 or 4 mini-magnets.

Permanent magnets really love to 1) stick to eachother when you don’t want them to and 2) repel eachother when you want them to stick. Hence, I couldn’t back the mini-magnets up against each other. Instead, I had to place 14 “keystone magnets” first, at the proper angular displacements, and make sure they were firmly in place.

Thin CA wicked into the gaps between the magnet and the can held them in place well, and was also more convenient than making a mess with epoxy. I printed a 1:1 template from Gobrushless to help with spacing the magnets. When I’m happy with the magnet arrangement, I’ll lock them in with said epoxy.

The round aluminum piece in the background is the original “failed test piece” which I turned into an axial spacer for keeping the magnets the right distance from the ends of the can.

14 metamagnets composed of 2 mini-magnets are installed.

At this point, I wasn’t too sure whether or not to proceed. 28 magnets around the edges give me a near-perfect filling. Unfortunately, this is actually disadvantageous to an extent, as past a certain field strength, core losses start increasing and efficiency suffers. On the other hand, I stand to drop the voltage constant of the motor even further, making a slower, and hopefully torquier motor. But only 14 magnets gives rather poor filling. If these were, say, 10mm or 15mm wide magnets, I wouldn’t complain.

Intermission! I took the advantage of having my fingertips covered in a thin layer of CA glue to wind the core. Here’s one phase completed. The winding is “distributed LRK” style, with two-stranded 22 gauge wire looped 24 times around each pole.

Unfortunately, even with CA-shell assistance, I still do not have Manly Engineering Fingersâ„¢ and doing this took quite a bit of skin off both of them. The stator was mounted on something solid so I didn’t have to hold it, but pulling the wires tight did me in enough. I need to go find some gloves or something.

So I gave in, and shoved the rest of the 28 magnets remaining into the can. Bryan, you can kill me later. I promise. Just let me get one test run in.

I had 56 magnets exactly and couldn’t stand ruining my circle. How’s that for vanity?

Additionally, I decided to designate one of the endcaps as a permanent mount for the stator. Currently, the piece is on the radiator with the epoxy setting. Why?

If you have ever pulled the can off an outrunner motor (or yanked the parts of any permanent magnet motor apart), you know the magnets are very much attracted to the iron core of the rotor. On largeish outrunners, this force can be significant. On this fucker, it’s insane, and I’m going to make a jig to mount the stator without killing myself. The first time I brought the stator near, it nearly sheared off my finger because it flew so fast into the center of the magnet ring. The only way I could get it back out was pushing on the stator as hard as I can while gripping the can. And then it wouldn’t just fall out, because it kept getting sucked back in…

Hopefully, with some überpoxy holding the can in the Designated Endcap, I can bolt this endcap onto something, say the bottom end of an arbor press, attach the stator to the ram, and slowly drop it in.

This must be why permanent magnet motors aren’t made too large.

Anyways, stay tuned for the last few updates, which should be coming soon, assuming I grow new fingers by the time summer arrives. It’s almost moving!

Introduction to Improper Machining Techniques

chorl

So I’ve used alot of “improper engineering techniques” while making some parts due to either a lack of proper tooling, actual experience/training, or desire to take a few short cuts (teehee), so I figure I’d document them here. Mostly it concerns lathe work, since the milling machines I have access to are rather well stocked. A running list, which will be updated as I find new and more unsafe ways to make my parts, is here:

1. Counterdrilling. Obsolete since we got real center drills, but before that time, I managed to start holes with a countersink. The multi-flute ones have a symmetrical pointed tip, often with remnants of the ground flutes running to the point, so it was easy to dimple the part with the countersink in the tailstock. Then I used a small drill bit (usually 1/8″ or less) and piloted the hole. Then I enlarged it to whatever size it needed to be.

2. Not-Boring-Bar. We still don’t have a proper boring bar setup, so I decided to grind one from a stock carbide turning tool. It had its issues, but once proper clearances and draft angles were ground, it actually worked great. Due to the nonadjustable tool angle, some times I have to fudge with how the toolpost is set up to have it actually cut (or cut well and not just make a loud screech), but that would happen with a real boring bar also.

3. Steady rest centering. Since I never took an actual machine tool class, I’m not sure how the professionals get their workpieces all centered and true (past using a dial indicator and selective mallet bashing), but I found a bit of solace in the steady rest. Any time a piece sticks out more than half an inch or so, I can squeeze the thing in there and center the piece. First, the chuck is tightened lightly, enough to not loosen when the spindle is turned on. Then the spindle is fired up and the little jaws of the steady rest are cranked down until they just contact the material. This almost always makes the workpiece run (decently) true, but I have to be careful not to push too hard with one, or else it will cock off to one side. Then the chuck is cranked all the way down, the spindle run again (to see if the aforementioned fault did occur), and if it’s good, the rest is removed and machining begins.

4. Amputee’s Cutoff Tool. The lathe doesn’t have a cutoff tool setup either, so the proper technique is to make half the part, hacksaw it off, then flip it over and make the other half.

Yes, that often means maniacally wielding a hacksaw with your arm hanging inches away from a giant spinning round thing with protrusions and a bunch of pointy steel bits. I’ve been told that other people cut further away from the chuck to avoid dismemberment, but I don’t have that much material to spare. Moving the saw back and forth does speed the cutting, but often I can hold it in one place and keep it there until it cuts through. Moving the carriage with the tool bit mounted close to the line of cut helps keep the saw steady.

Yes, the spindle is on. No, I probably won’t be allowed near any machine tool in the student shops again if the instructors read this post. No, MITERS does not have a portable trauma kit.

5. Differential gear oil mixed with automatic transmission fluid, knife honing oil, and some WD-40 actually make a pretty neat cutting lubricant mixture. Gives beautiful finishes with a slow power feed (that I subsequently smudge when I take the piece out). Just plain WD-40 also works, and has the added upside of making huge smoke clouds on large diameter parts which I use to frighten new MITERS members.

6. Face-drilling. No, this does not involve using my face to drive the drill bit. Due to (again) the lack of a cutoff tool, I find it easier and safer when working with small diameter rounds to take a giant drill bit and just drill down the round stock to the dimension needed. A slight waste of stock, but if I size the stock right, wouldn’t matter anyway. The picture linked was me drilling down a 1/2″ bolt to make the Extend-O-Shaft 2000 for TB4.5.

7. Ghettoedging. One of the only techniques I had to use on the milling machine before I 1) found the edge finder at the Media Lab and 2) got edge finders at MITERS. The technique is simple. Color the edge to be located with a Sharpie marker. Then load up your favorite endmill. With the spindle running backwards, slowly feed the material in, and stop as soon as the first bit of sharpie disappears. Raise the endmill by the quill/column/whatever suitable Z-axis part, account for the tool radius, and start on the next edge. Don’t forget to run the spindle right way when you’re done.

It worked great on the ML’s junky import mill-drill, since with every tool contact there would be loud vibrations through the whole machine (and the… filing cabinet… it’s sitting on). With the giant Bridgeport at MITERS, it was alot harder, since all the cast iron and concrete floor would absorb the tool vibrations.

8. Ghettocentering. Combined with the Steady rest, it’s all I need to make true parts on the lathe (okay, true within reason). Drill bits have shanks which are usually the same diameter as the rest of the tool. Shanks are solid, round, and very close to the chuck, which is mounted in a stiff tailstock. If I need to remove the part for any reason, I make sure to drill a center hole first (using as large a bit as the end part would allow). Then, when the part is replaced, I can slide it on the drill bit shank first, then clamp it down in the chuck. It keeps the part centered axially as well as radially (within reason). I can then follow up with the steady rest. Or, on occasion, I can manage both at once.

There’s probably more that I can’t think of at the moment, but rest assured that this post will pop back up on top if I break some new ground (or some parts, or me.)