Tag: robot

Random project updates

chorl

I remember two weeks ago when I said that I would build nonstop through the break; anything I could think of, and come up with more things if I ran out. Anyways, that totally went to hell. But progress is slowly coming.

I’m in the process of completely redoing the Snuffles Reloaded wheelmotor. The previous one was okay for getting the concept to materialize into something solid, but was done across 3 different machines and with little regard (or ability) to center the workpiece properly.

There are also some design changes this time around. Most notably, I’m redoing the magnet can out of steel to better fit the very strong magnets that will be used, as well as to simplify things.

The finished product. This was the single most torturous piece I have done yet. Steel of this diameter needs to be turned reeeeeeeally slowly. I mean like 70RPM slowly. It was very hard for me to keep my feedrate down (because I’m used to small aluminum parts), and if I went too fast, I would just be cutting shallow screw threads.

Not to mention that it was a hot-roll steel pipe that I carved this out of, so the steel was total shit and was gummy. The surface finish is horrible, but it’ll live. The perimeter holes were put in on a CNC machine (most awesome thing evar, only matched in awesomenss by a 5-axis abrasivejet. The two combined can carve the laws of physics and grammar such that they can both be most awesome.)

I’ll do the aluminum parts later. I might possibly redesign some of the internals to make the parts less weird.

In TB4.5MCESP1-related news, the arm controller came.

Ooh, shiny. This is a Syren25 single-channel controller from Dimension Engineering. It’s a nice piece of work, and supposedly features regenerative braking. That’s hardcore. So having opponent bots backdrive TB4.5’s lifter could actually be a good thing, but they should do it slowly and gently!

Since I was going to remount the ESC on my own heatsink plate anyway, I decided to take a look at the underside where the driver chips are.

O GOD WAT

NO! NO NO NO NO…. For the love of Robot Jesus Michael Fizgerald Jackson Christ! SO-8 surface mount FETS?!

I am SO GLAD I’m mounting this thing on a plate of aluminum that weighs more than it does.

I hate those tiny SMT FETs. Especially when the manufacturer (generally of brushless controllers) use like 20 in parallel to get a decent amp rating. What money and weight do you save then?

It’s even worse when you listen to the chip maker who says a 25A part is a 25A part. The SMT has absolutely no thermal mass and no capacity to withstand momentary overload. In fighting bots, you NEED THE OVERHEAD. I’m sorry, I will NOT run 25 amps through this thing for any extended length of time, and am very glad the arm is an intermittent duty cycle.

I’m making my own ESCs from now on, or I’m never building another robot of any kind.

Oh, and the heat spreader plate doesn’t contact the driver chips. That’s even less of a 25A ESC. DE might want to consider backing off the pressure a bit on whatever press that is stamping the aluminum sheet.

Anyways, time to actually start building the bot. The carbide teeth on the miter saw’s new blade are slowly subliming, so it’s best to use them while they’re still fresh.

TB4.5MCESP1 Update 4 and another vaporbot.

chorl

New plan! Again!

Due to some unforeseen characteristics of the Banebots 12-45, my plan of adding thermal mass to the electronics bay won’t work out, at least not without more precision engineering than I am willing to put up with. This coupled with additional budgetary concerns means that I’m keeping the Victor 884s. There’s nothing wrong with them, and they are in fact very good controllers. However, the reason I wanted to move away from them was due to size issues – they’re not exactly compact.

But most of the time, big and beefy lasts the longest and is the most reliable. Here’s a temporary drawing of what the new internal arrangement will look like. I have yet to model the mounting plates.

This is roughly the same as in MCE – battery, power switch, and arm controller (the Syren 25 is staying) on the right side, and the drive controllers and receiver on the left. With increased space in the middle of the bot, I can mount the Victors longitudinally as shown, but there is really no advantage to it as the arm controller wouldn’t fit in the space between them and the drive belt. So to free up space for wiring, I might just keep the widthwise mounting of the 884s.

I hate scaling back the Grand Master Plan, because now there really is no upgrade besides a lithium power system and possibly higher grade alloys for the wedge and arm – “possibly” because higher grade alloys cost more, and so that planned upgrade might not happen either.
Whoopee. Now that SP1 is looking more like a bugpatch, I’ll unveil the latest Team Test Bot vapor design.

Trial Bot 1.0, way back in 2005, was my first attempt at building extremely low bots. It was an overhead horizontal kinetic weapon design, an inverted lawn mower design (even had a 22″ lawn mower blade). At the time, it had ground-to-blade height of 2.25 inches, which was obnoxiously flat, but suffered from a multitude of engineering problems: low ground clearance made worse by non-countersunk chassis bottom screws, an unreliable friction drive mechanism, and a tendency to become unbalanced and ping itself.

With the wide-scale commercialization of high-performance lithium polymer power systems and brushless motors, I can do much better.

Yes, that’s right, a ground-to-blade height of 1.6 inches, which, numerically, is smaller than most bots’ wheels and right around TB’s three-quarters mark. The chassis is 1.125″ thick, and was designed to be aluminum, since UHMW of this thickness would be unbearably floppy. This is only possible with customization of just about everything. The frame is thin enough to be made as one piece using an abrasive waterjet with draft compensation. Notice the ersatz-tank tread drivetrain, which gives the effect of “4 wheel drive” without needing a separate belt and pulley assembly. This will be accomplished using urethane round belt, like NK, or some really big o-rings. There are three on each side for redundancy, but I don’t doubt the bot can just take off and land somewhere using the blade if the drivetrain is disabled.

At the center of it all is a very large brushless outrunner motor, similar to Pop Quiz – in fact, PQ was built to test the viability of direct drive weapon motors in larger bots. As designed, this motor weighs almost 3 pounds and has alot of solid metal on it. The mount also attaches directly to the bot frame to make the whole assembly as stiff as possible. A copier motor will supply the stator, which will be 70mm in diameter by 20mm tall. Motors of this size are commonly used to fly model airplanes weighing 20 to 30 pounds.

Note the triangular cutout at the back. This is a by-product of designing the bot with a base size of 12 x 12 inches, common to all of my 12lbers. However, this leaves most of the interior empty because of more power-dense, hence smaller, components. The bot can be shrunk to 10 by 10 inches easily and make more efficient use of the space as well as free up weight (for a bigger blade!), but I’ll worry about it when I actually have the ability to build it.

It’s fun thinking about future designs, but 2008 is approaching and I need to get to work on SP1 – the parts pile is condensing from the bot-aether.