More than a month has passed since the last LOLriokart update. Does it move yet?!

No. I really haven’t had that much time to sit down and perform the design work that is necessary to generate parts. Since I’m practically doing all of this on-the-fly, I need to consider how future parts (i.e. the ones I’m making in 5 minutes) are going to fit with existing ones, and how they might or might not get in the way of things not yet designed.

Now consider that my weekly obligations tend to be sporadic, and that it’s the end of the semester, so everything is coming down to the wire. Throw in a few distractions like finishing the scooter and you get that the plastic milk crates holding up LOLriokart are slowly indenting where they meet the tube frame because it’s been sitting so long. Creep under continuous stress, or something…

But there has been progress made. I’m steadily pushing forward on linking the front wheels together and connecting them to the steering wheel. After that, the intent is to get the front brakes working. Then I’ll have a rolling chassis which can accept whatever powertrain I feel like building.

Here’s the progress over the past few weeks.

So the steering column will have two segments and three supports. The lower half is vertical, and is supported at its bottom and top by bearing blocks. The bottom support was easy – a bushing mounted to a segment of thick-wall aluminum rectangular tube, which is in turn split-clamp mounted to the original crossbeam which the shopping casters mounted to. This placed the axis of the shaft in a good position close to the front of the basket cutout, which is what I wanted.

The top support for this vertical section was harder. I didn’t have any billet or barstock of the proper size, and I didn’t think the aluminum tubing was going to be sturdy enough given that the wire frame provides no flat mounting surface.

Then Robot Jesus descended from MechE heaven to present me with another near perfect scrounge part. Now I really want to know what this crazy machine that was parted out by MITERS many years ago was – it has saved my ass a few times already.

And so it was that strange trunion-like thing with a 1/2″ Bronze Bushing of Convenience (+1?) only needed about a quarter inch trimmed off the flat side to align the steering column perfectly vertical. It even had large threaded holes on this side to mount on the basket!

Unfortunately, the front of the basket has an even number of vertical wires. The trunion-thing has an even number of holes. Since the bolts need to pass through the empty spaces between the wires, I wasn’t going to get a centered steering column with the stock trunion. No problem – while set up to take 1/4″ off the top, I drilled new mounting holes right between the existing ones, for three in total.

I also threaded the holes in the same setup, using the mill in low gear (and my big keyless chuck) to powertap the 3/8-16 threads. Apparently, I scare the crap out of everyone who sees me powertap on the mill. But it’s no problem if

• The tap is huge, so it won’t just snap from the torque
• The holder has some sort of clutch effect (clutched tap holders for mills are made especially for this purpose), or is huge enough that anything holding it is going to slip anyway if it is clogged or bottoms out. For more insurance, loosen the belt tension on the motor.
• The quill is allowed to move freely, so the tap can pull itself in and out
• You’re really fast on the motor switch.

With this setup and some mechiprudence, I have powerthreaded holes as small as 1/4″ and as large as 1/2″-13. The latter was pretty ballsy.

So what, I’m not beefy enough to crank large taps…gotta find a solution!

Next was the other side of the assembly.

To secure the shaft support from the other side, I quickly cooked up this clamp bar with 3/8″ through-holes.

Whole assembly fitted. The little rounded cutout on one edge is to hang onto one of the horizontal wires to keep everything more steady. It was made using a radius-tip (not ball-tip, just radiused) cutter that I got in a toolpile from Ebay.

This is yet another extremely overbuilt impromptu part that should never fail. If it does, I’m probably spread into a very fine film already, and thus would not have to worry about repairing it.  Other parts of this nature on LOLriokart include the steering brackets, rear bearing blocks, wheel hub and mounts, and… oh, wait.

I love billet aluminum.

Let’s move onto the steering linkages. While the big aluminum tube acting as the steering tie link was nice, it’s just too bulky. I came up with a new plan involving ball joints (or “rod end bearings”) and threaded rods.

A large threaded rod connects ball joints at both ends of the tie link assembly to a rigid center piece which mates with the eventual Pitman link (that in turn is rigidly mounted to the steering column). The ball joints go to the steering links on the front wheels.

It was Thursday night, and if I ordered ball joints from McMaster, they’d ship Friday morning, get here Friday evening, and be stuck at Shipping & Receiving all weekend. I don’t have the patience for that kind of stuff, so I just rolled (milled?) my own rod ends. Fortunately, the Media Lab guys bought a basketfull of ball joint bearings for the car project a while back, and ended up using a handful. I nipped two and carved some aluminum holders.

Installed. There’s a 1/2″-13 hole on the back side to accept the threaded rod, which I manually tapped this time. It was a great exercise in how to start a giant tap straight, and just great exercise in general.

I ended up using two steel pipe sections, 18″ long, as handle extensions on the tap wrench to give me more leverage.

Assembled. The ball joint gives about 10 degrees of tilt and roll in the steering linkage. I won’t need this, but it was nice to have, since I’m sure nothing is actually aligned properly.

Normal people would have welded all of this up and have been done in a day. I, however, have a disdain for welding because it’s just too permanent. Yeah, no such thing, right? I like having the ability to take my stuff apart. This will all come apart into neat aluminum billet pieces when I’m done – not ugly, globby things I have to hack off with a grinder.

Let’s hope it doesn’t come apart into neat aluminum billet pieces while I’m driving it. Maybe that’s why we weld…

I suddenly had a change of plans while building the linkage ends. Instead of using a single threaded rod, I could use two separate ones, and have the ability to tune the toe angle by moving the rods in and out and locking them in different places. Even better, why not use some big Grade-8 cap screws?

So the plan then became using the rigid center piece as a bridge between the two cap screws, using a clamp-mount type assembly at both ends to hold the cap screws right behind their heads. Thus, if I needed to tune the toe angle, I could loosen the clamp, turn the screws a bit, then lock them back down.

This meant I had to make the aforementioned rigid center piece longer than if I had just ran a threaded rod all the way through, which means I have to go buy more bar stock since it exceeded what I had available by a factor of 2. Effective use of available materials, people!

Or maybe I should go find cap screws 1.5 times as long?

Alright, enough fun for now. This is LOLriokart as of two days ago. It has clearly evolved from a shopping cart full of shit to a slightly more fancy shopping cart full of even more shit.

Ah, but useful shit.

This is probably all that will happen until I return from Atlanta for the remainder of IAP. However, I can still work on modules and parts while I’m in Atlanta – just won’t have the opportunity of knowing I’m doing something totally wrong mid-process.

One assembly that I intend to make in Atlanta which will make the project that much better, is a rear differential. As long as I’m not building a wheelmotor for each wheel (Hey, maybe that will happen in the future) and it only has rear wheel drive, then I should probably add a differential to the axle. Otherwise, the two rear wheels will try to rotate the same speed through a turn, which as anyone familiar with vehicle dynamics would know, is…bad.

I’ve sort of held off on this for a while, since getting the solid axle version running was a priority, but as long as I’m taking this long on everything, I might as well. Here’s the plan.

Wait… What the balls is that? That doesn’t look like a differential! There’s not a single bevel gear! This looks like a differential.

Correct. This is a design known as a planetary differential or a spur differential. It uses the principle that two mating spur gears rotate in opposite directions to produce the same action that a set of bevel gears does.

The two output gears are separated by a gap. Each output gear mates with a small, long pinion (longer than its diameter, such that it bridges the gap, but stops just short of touching the opposite output gear). The long pinion of each output gear in turn mate with eachother in the gap.

Result? Let’s rotate one output gear clockwise. Its long pinions will rotate counterclockwise. It mates with the long pinion of the other output gear, rotating it clockwise. In turn, the other output gear rotates counterclockwise, the opposite of the first. This is the same action that bevel gears provide when put into the classic box arrangement seen in open differentials. You may multiply the number of long pinion sets around the perimeter at will to get more strength.

Using helical gears and a slightly different arrangement gets you the Torsen type limited-slip differential. That’s an exercise for another day.

Benefits: No weird (expensive) gears. No weird geometries to machine. Can be made using standoffs, bolts, and stock gears. That’s what I intend to do. Except just big, so it can take the torque of the Etek.

Speaking of what the balls, I also drew up plans for a giant ball differential (as seen in R/C models) a while back, but at this scale, the design will be very inefficient.

Onwards!!

In nuclear physics, criticality is when a chain reaction becomes self-sustaining. In MITERS physics, criticality is when your project can actually support its own weight without being propped up by 2x4s. It’s only taken me six months to put 4 wheels back on the kart (which can now function as a shopping cart again!). The driveline mechanics and steering linkage are still not complete, but at the very least, it can be rolled around at will to clear space in the lab.  So, naturally, it’s picture update time.

After making a mirrored set of bearing blocks, it was time to test the axle alignment. Either my parts aren’t square with respect to the cart frame, or the cart frame is just not square at all, but it takes a bit of malletwork to push the axle through. I have to keep the retaining bolts pretty loose during axle service also.

I thought of a few workarounds like remaking the double blocks from one single block, or using self-aligning mounted bearings, but put it off to work on the rest of the parts.

Temporarily mounting a drive hub to test fits and clearances. As expected, I’d need a shaft collar on the outside of the bearings to keep the tires away from the mounting bolts in addition to the collars on the inside. I may end up making this one large shaft-block-spacer assembly to reduce partcount.

With the rear tires bolted on, it was time to drop the thing off the milk crates which have acted as a work stand. Here’s the first “on-the ground” test. Not much a test, since it had no steering linkage or drive components, but it was a good chance to test the rigidity of the entire system by jumping in the basket and rocking around. Verdict: I approve.

Let’s get to work on the steering linkages. Out of the same mysterious machine that supplied my brake-o-hub original material come these trunion-like things. Each one is a one-piece machined aluminum block with a bronze bushing in it. How convenient – they seem like just the thing to turn into steering arms.

The left part is the original part, and the right the finished steering arm. I had to cut down much of the material to get to that stage, but it was the most compatible with the months-old steering knuckle design, and also an excuse to make the space smell like Tap Magic.

Test mounting the finished part. The chamfer allows a farther range of motion in that direction. Normally, the edges of the knuckle blocks themselves act as the hard travel limiters.

The combination of hard machined lines and angles give the front end a rather distinct look that I rather like.

So remember how the bearing blocks weren’t exactly square with the frame? They actually not square with themselves either. Small variations in how the steel tubing cart frame was welded made aligning the bearings to pass the shaft through extremely difficult.   To alleviate this, I made an inter-block spacer with pilot circles that snugly fit the bearing bores. At the very least, this forces the bearings to be square with eachother. The two sides may still be out of square, but retaining bolt holes can be fiddled with.

After properly spacing out both sides, it was much easier to remove and install the driveshaft. Speaking of which, I milled double flats on the ends to give the hub screws something to bite onto. The shaft is also internally threaded on both ends, so I can at least have something physical interlock (like a bolt with washer) between set screws and certain death.

With both linkage arms made, it was time to try and link them together to check out the steering geometry. The spirit of the mysterious machine supplied these dual-bushing aluminum spars which, by some chance alignment of Cybertron and Earth, was the exact length to provide perfect straight-ahead wheel alignment (Any toe angle is too small for me to notice).

And so the first inaugural test run of the kart was completed, with three people involved : One to ride, one to push, and one to flick the steering.

Steering linkage in (mostly) straight-ahead position.

….and at maximum departure from center, turning right. Notice the difference in angle of the wheels – this is an attempted implementation of the Ackermann steering geometry, which is what modern car-type steering is derived from. That’s the reason I took the extra step to make the steering arms offset to one side.

So that’s all for now. Even though the big aluminum link was fun, it will probably be replaced with some big tie rods to allow for fine adjustment. I have not planned out how to actually attach the steering wheel to this linkage yet, nor have I designed the motor mounts or rear powertrain. Or anything for that matter – the entire kart build so far has been design-and-build on-the-fly. I don’t know what parts I’m making until 5 minutes before I actually make them.

The primary goal is to get the steering and front brake system working, since that allows the kart to be used as a rolling chassis for any number of different propulsion methods.