LOLriokart Update 3

chorl1 Comment

I’m starting to think that LOLriokart might be an ongoing project for the fall season. Reasons mostly revolve around increased day-to-day time constraints and the fact that it’s already mid-July. Ãœberclocker and Pop Quiz 2 take higher priority right now, since Dragon Con is at the end of August and I’m also heading back to Atlanta around mid-August, leaving roughly one month. Additionally, I need to start getting some green-colored ducks in a row for fall semester (something is surely amiss – they want me to cough up how much money!? In 3 weeks!?)

Shenanigans. Anyways, a 40 pound box of heavy industrial metal landed on my desk at the Media Lab today, and it was from Surplus Center. Inside it were almost all the necessary implements to transmit motor power to a set of drive wheels.

And so this is the cumulative pile of parts, including everything from today. Starting from the top left and orbiting counterclockwise,

  • Battery bars from dissecting the large NiCd packs
  • A 36″ long, 3/4″ diameter keyed shaft, the rear axle. Surplus Center stock item.
  • A box of #40 double-row chain. Oops, when I saw “#40-2” I thought they meant 2 feet. Now that I check the Surplus Center catalog page, it indeed says #40 double strand, 10 feet. Questioning own sanity. I wonder if it’s okay to use half of a double strand chain.
  • A gaggle of little flanged bushings. I got the smaller ones from SC at 50 cents a pop – they will most likely be mated with the steering shaft. The big ones were scrounged.
  • Two band brake assemblies from small electric scooters. I had one a while ago, but it was significantly larger – I didn’t really expect these things to be so tiny until I actually got them in the mail. Fortunately, the front brakes are only for bringing the vehicle to a full stop, complementing dynamic braking, as well as locking the front wheels for epic burnouts. Nothing high-energy.
  • A small universal joint I got in case I wanted a better steering position, from SC.
  • 3/4″ shaft collars for the above rear axle, also SC.
  • Epic #40 unbored sprockets. I knew #40 was huge, but I didn’t realize how huge until I found out each sprocket weighed 5 or 6 pounds, is .3″ steel, and 6 inches in diameter. I will bore them out for the 3/4″ shaft, but since I have no reasonable access to a broach, they might have gigantic set screws embedded in them. From where else BUT Surplus Center?
  • Little #40 sprockets for the Etek, ditto.
  • A cluster of bicycle coaster brake hubs. They’re probably not going to be used for anything. All of them were scrounged for some front brake ideas, but are now obsolete.
  • A bundle of bearings. There are four 20mm ones, two bigger 20mm ones, four 3/4″ ones, and an assnormous double roller bearing of some sort. I forgot where the gigantic bearing came from, but it looks like a machine tool spindle bearing. The 3/4″ bearings were ordered from McMaster since I also have a 3/4″ shaft – the 20mms were scrounge, but would have required machining a giant steel rod down to match them.

This is some Serious Fucking Metalâ„¢. The only thing Surplus Center could have included to make it even more industrial is some Nine Inch Nails albums.

Experienced users of chain know that raw, unprocessed chain comes in cakes form, and must be baked properly.

Oh, wait, the caking is just from the fermented packing grease… I actually had to break the cake apart by yanking on the chains links. The chaincake is a lie.

I was lucky enough to find matching sprockets for the motor, so these little sprockets require no modifications.

After sorting out the industrial grunge, it was time to turn my attention to design. The front wheels on LOLriokart have been a quandary for a while now. I wanted mechanical front braking since the motor controller can perform regenerative braking on the rear axle, and a mechanical rear brake would just be redundant. Also, mechanical front brakes means I could perform tricks that require weight shifting (e.g. initiating drift).

I went through a whole bunch of ideas, which are listed in an earlier post, but in the end, I broke down and got the scooter band brakes seen in the picture above.

Now the problem was implementing them. Their brake cups didn’t really match any of the other parts in terms of dimensions. Their bore was too small to fit over the stock bearing hub of the pneumatic tires, yet too thin to machine. The wheel hub itself didn’t lend itself to much OD modification as the bearings took up most of the inner diameter. I could make a custom hub, but that would require processing a 3″+ aluminum round, and with the horizontal bandsaw broken down at MITERS, that wasn’t going to be fun.

A solution had to come from something that was round and already sitting in a bin somewhere. Conveniently,these big aluminum hub-like doohickeys fit the bill. With a 4″ diameter flange, 2.5″ diameter body, and ~1.75″ bore, they could slip over the existing bearing hub as well as accept the wheel hub’s bolt circle. Since all the brakes require is something about 60mm to run on, I could turn down a bit of the end to 60mm and just use that as the braking surface.

So that’s what I did. I turned the flange to 3.5″ to fit inside the wheel rim, cut the last two inches of the body off, then turned down a section to 60mmm.

A pass on the mill for a wheel-matching bolt circle and the new Brake-O-Hubâ„¢ is done. Four 5/16″-24 (weird thread, because I had ’em already) screw into the aluminum hub to retain the wheel and its bearing tube. The Brake-O-Hubâ„¢ slips over this tube and extends past the wheel profile enough to stick into the brake bodies. A spacer will eventually keep the two apart the right distance while allowing me to slam the whole assembly together between a 1/2″ bolt and the steering knuckle.

Other side. These wheels are similar to the cheapo handcart tires commonly sold at discount hardware places, like Harbor Freight. They have a stamped steel rim and a welded-and-stamped bearing hub tube thingie that is wider than the tire. Since I only needed one half of this tube, I cut the other half off and moved the bearing into the newly shortened hub.

No need for a 6″+ bolt cantilevered from the steering knuckle now.

I’ll be making one whole side of the drivetrain first, so I know what to do (or what not to do) for the other half. Things still unsorted include the actual steering linkage, how to securely mount the brake bodies (and how to actuate them), constructing the steering knuckle, and figuring out how to assemble everything.

And that’s just the front end.

Bot on?

Ãœberclocker Update 6: The Beat Goes On

chorl

It’s been a while since I’ve had an entire day of solid bot work. Most of the “weird machining” on Ãœberclocker is now either in process or over with. A few tricks and workarounds made things go alot faster.

…like this one. After exactly one part, I got sick of having to re-zero the machine after flipping the piece over. And so I had to devise some crazy rigged solution as usual.

Fortunately, this time, it wasn’t too rigged. A few 90 degree angle blocks were hiding in a shelf corner, so I cleaned the industrial grunge off one and mounted it to the mill table. A bit of threaded rod and some malleting later, and I had a makeshift “workstop“, which is a little stick-like thing that is used to accurately reposition a workpiece after removing it from the vise.

It’s slightly more than a stick, and looks like it can actually stop a small train, but oh well.

How do you drill a 9 sided hole? With a countersink. Although there were a dozen or more countersinks in the Toolgasm, none of them are odd-fluted. The result: chatter like Paris Hilton with a new cell phone.

It probably didn’t help that I just freehanded this part.

Fr0k spacing things all threaded. The same part that got me sick of edge finders also got me sick of manually tapping. Solution: spiral-point tap and a cordless drill. Spiral point taps seem to be an order of magnitude stronger than their four-fluted hardware store cousins, clear their own chips, and a nice handful came with the Toolgasm. I selected a TiN coated #10-24 and tore through all 24 threaded holes in a few minutes.

Unfortunately, 16 of those ended up needing to be clearance holes. Oh well, better that I thread 16 extra holes than drill 16 holes too large.

In another fit of absurdly industrious machine work, I finished up the “upper fr0k”. To my chagrin, I discovered that 800 grit fine sandpaper produced the same shiny finish as a fine power feed. So I just made a bunch of standoffs from raw half inch aluminum stock (of which there was a convenient 10 foot stick, found behind yet another unsorted shelf). The front support leg standoffs were made this way. I decided to not bother shining up the spacers for the upper fr0k.

These were also power-threaded with the same #10 tap, on the lowest speed setting of the lathe (something like 100 RPM). I set the belt tensioner a bit loose such that when the tap bottomed out, the spindle stopped turning.

Outer fr0k tines mated to their respective spacer things. The 15 degree lead angle on the spacers have been milled in this picture, and is just barely visible (They won’t do a thing… why the hell did I even design those in?)

After putting down the fr0k, it was time to attack the first “weird machining” task – making the 10 degree front and rear slopes. This was made decently difficult because the parts were huge (15″ long UHMW) and I had no angle blocks, angle vise, angle plates, or any other implement with the word “angle” in it besides “angle grinder” which didn’t help one bit in this case.

I ended up pulling the same stunt as when I machined the 45 degree front slope for Pop Quiz – tilting the head and using Interesting Trigonometryâ„¢

It worked pretty well. For every n” I moved the table up into the cutter, I had to move the x direction n / sin(10°) to keep the cutter face on the same plane. Repeat k times for k a small real integer constant and a 10 degree slope emerges. Then flip the part over and do it again.

After all four rails were roughly shaped, it was PRETEND-O-BOT time! Hey, it looks like something.

This thing is absolutely enormous. That’s a 36 inch T-ruler I used to position the parts. The chassis itself (UHMW only) is 15.5″ long and 20″ wide. The fr0k extends way out in front and brings the total length of the bot to 27 inches. That’s pretty nutty. For comparison, TB4.5MCESP1LOLBBQ is exactly one foot square (one square foot?!) with the wedge bringing it to 16″ long and 16″ wide.

While I was still on bot-gasm mode, I trimmed off some of the 1″ UHMW barstock for the back end. Also notice the similarly-sized aluminum bar. I originally purchased this for the LOLriokart (whose drivetrain parts are still in transit. Thanks goes out to Bank of America for assuming any purchase I make over $100 is some kind of fraud unless I tell them beforehand that I’m buying something more than lunch)

I’m debating whether or not to just make the back end of the bot out of aluminum. The bot is 7 pounds underweight in the design, even with most of the big hardware accounted for. Since there’s no way I can fill up at least 6 pounds just with wires, Loctite, and duct tape (by accident), it could stand some more solid material. Aluminum would also double as some ballast to keep the bot on the ground during a powerlift.

Stay tuned for more! United Hobbies/Hobbycity should be pitching some 4AH lithium polymer packs at me soon.