Team Test Bot Pre-Dragon*Con 2008 Botgasm, Part 1

Wednesday, August 6th, 2008 @ 5:21 | Bots, Nuclear Kitten 5, Pop Quiz 2, Project Build Reports, Überclocker

It’s official – I have gone insane. Two weeks before my departure to Atlanta for a “vacation vacation” and Dragon*Con & Robot Battles, I have started on a new bot.

Yes, it’s Nuclear Kitten 5.0. Slightly revised again from the previous design as my experimentation with a new building paradigm.

The story goes like this. Big Blue Saw is running a free parts giveaway to raise awareness of its business. The parts are limited to a 9″ x 9″ square of either 1/8″ aluminum or acrylic. In a moment of engineering epiphany (or perhaps madness), I realized that NK5 could potentially be made from assembled 2D shapes cut on the waterjet. I learned this technique of building from working with the Media Lab guys, who regularly make large 3D assemblies using 2D cutouts. I got some practice this summer by building my awesome disc things, which are concept models for the Citycar test platform.

So I designed a “Chinese Puzzle” style chassis for NK5 over the course of a night. Here’s a 2D experimental layout of the first revision of this chassis, using slightly different corner attachments. Sadly enough, the sheer number and complexity of the pieces put me way over the “free part quote limit” – by about 300%.

However, the lure was just too great. I refined the design to reduce the number of parts and increase the stiffness of the whole thing, as well as make sure each connection has a physical interlock and isn’t dependent on just slip fits and screws. I also spent more time going over the entire thing to make sure there were no “impossible objects” – like tabs wider than their slots or impossible assembly procedures.

One fine afternoon (i.e. “yesterday”), I scrounged a piece of 1/8″ aluminum from MITERS and headed over to the  Media Lab.

But first, a prototype. After the last epic partfail, I have learned that it is wise to wreck inexpensive material first  than to just stab your stock with whatever the machine does. This was slightly different – I wanted to see how the frame would go together.

Using the GIANT LAZER and some 1/8″ model plywood, WoodeNK was born. I am very tempted to actually make the bot from wood. The good news is that everything goes together as planned.

…and so the design was transferred to aluminum on the waterjet. Careful file inspection and a bit of manual pathmaking made sure that the very complicated combined profile was cut correctly.

Unfortunately, in a strange turn of events, my camera decided to kick the bucket last night, so this is the last “good” picture of the frame.  Initial inspection of the interior and listening to noises tells me that the lens mechanism is jammed. Since I’m rather harsh on my equipment, I suspect a good dose of pocket swarf or some industrial grunge from MITERS might have found its way into the mechanism (which is surprisingly exposed for being behind a shell).

A year and two months. Hmm, my last camera died during the TB4.5MCE build… I might take a stab at repairing this one, but as with all modern miniaturized electronics, it might not be worth the effort.

Some progress has been made on Pop Quiz and Ãœberclocker also.

Pop Quiz

For the past few weeks, PQ has been sitting on my desk within arm’s reach, but I haven’t worked on it at all. In fact, I had to constantly shuffle things around to actually do other things on my desk. But with Ãœberclocker awaiting some 1/16″ aluminum, I got back on it.

The first order of business was to rig up a master power switch of some sort. This was actually quite difficult due to the bot’s height. Currently, Pop Quiz uses a separable link as a switch – essentially just the main battery pack connector, accessed through the holes in the top plate. Not a very secure design, since the connector can – and has – fallen out of the hole and into the path of the blade while spinning.

Electrical self-eating is a shitty way to lose a match. I settled on a hybrid pushbutton switch setup using some right-angle panel mount switches. I have a whole bag of these things from an AHRC meeting from two years ago, and they have been begging for a use. While the switches themselves say “0.4VA MAX”, the contacts are all solid brass and quite substantial for a switch this size. I figure this can’t be as bad as thin aluminum tabs on the Lipo cells.

Here’s the switch mounted in the sidewall of the bot. The panel thread was either #10-uber-fine or 5mm, but it force-threaded into a #10-32 tap hole.

A nut and a dot of CA glue secures the switch axially.

Next, I threaded in a set screw from the other side.

Result? Hex wrench-actuated main switch. When the screw is tightened, its tip pushes the momentary button switch down and the bot activates. Turning the screw counterclockwise allows the button to spring back up and the bot turns off. This should never trip by itself in battle, because that would involve somehow ripping the screw out of the bot, which means I probably have bigger problems.

I dubbed this the “Why-not-chi” switch after a commercially available switch for larger bots.

The balancer connector for the Lipo pack is thus the only thing that should be accssible immediately from the outside of the bot. It will get its own slot in the top plate.

The above picture is actually the last one I managed to get off the camera before it refused to power on again. So, no pictures of the actual wiring rig that I hooked up, which probably qualifies as the worst rat’s nest job I have ever put together. In something this tiny, it’s hard to keep the wires straight, especially 22 gauge with thick insulation.

The only thing I have not fully installed in the bot is the receiver and tiny mixer. The receiver will need some modification to fit under the cover plates, and both parts will have their servo connector pins removed and the channels hardwired to eachother, effectively becoming one package. There’s only space to accomodate this and some wiring.

I also have to solve the problem of “how do you get reception in a bot with 4 open-frame motors, a huge ring of spinning magnets, high-speed switching controllers, and two massive conductive ground planes (the carbon fiber panels)?”. Custom base-loaded antenna is one option, or take advantage of the fact that CF is conductive and make some sort of slot antenna. Or both.

Or neither, and just amp up the power of my transmitter to overpower everything else in sight, as well as control every 75Mhz R/C model within a mile.

Pop Quiz is only missing a blade at this point, and I have a sheet of titanium on the way for that.

Ãœberclocker

Ãœberclocker doesn’t look much different than before, since there hasn’t been much done in the past few days. However, I did take myself up on my own word, and have swapped the Mabuchi 550 frame drive motors for the beefier 775 motors.

The drill motor shells already had the 700 mounting pattern molded into them, but no holes, so  I had to drill out the appropriate holes. I decided to just swap the entire drill housing since the black nylon ones appeared more durable than the ones already in the bot – which already showed some crazing and characteristic discoloring from being under strain.

A #9 drill bit opened up the drill pinions to an elegant Loctite-assist press fit for the larger motor shaft

I also made these “inter-side rail stiffener blocks”, which give the front half of the drive pods something else to keep them steady. They were a bit flexible due to the single-point attachment in the front.

Unfortunately, adding the larger motors meant that the Victors are now a bit cramped. There’s no problem with wire access, just that everything is a bit closer together than I would like.

Ãœberclocker only has electrical work left, including making the servomechanism setup for the fr0ks. Some “EBay” plates will be cut out of 1/16″ aluminum and folded to shape to carry the electronics, including the battery.

So, how on earth do you get a 30 pound robot with an almost a 4 square foot top-down profile from one city to another? One method is to build a crate and ship it. Unfortunately, arranging shipping logistics both ways and building a crate is going to cost a good chunk of money.

30 pounds is just under the margin of how big a robot you can bring on a plane. So that is what I intend to do – just fly the bot as checked luggage. Many people have done this before. I do have a suitcase that is large enough to hold the bot – the one I brought all my shit up here to MIT with. However, you can’t just throw a robot in a suitcase, especially not one that’s this pointy. The suitcase is not hard shelled, so having something big and metal inside is probably bad news waiting to happen.

To overcome this, I decided to design an internal skeleton for the suitcase that will securely retain the bot in transit, as well as snap out of the case to use as a “bot dock”.

This is the “bot dock” portion of the design. It suspends the wheels of the robot off the ground, a critical disaster-prevention step checked for at many events. It’s just a few slats of wood selectively cut to let the bot slip into its center.

More importantly, it secures the clamp arm and the fr0k from moving when the bot is in the pits. This is also a safety procedure – the fr0k has easily enough torque to shear body parts off, and the front of the bot is a pretty big pinch point. The clamp arm, although less dangerous, is better off secured. This botdock
makes sure both parts are immobilized.

Next, there is a similar structure in the suitcase that holds this bot+dock combination.

Yes, I actually measured out the internal dimensions of the thing. Two side plates and 3 crossing slats, which will all be secured to the suitcase by wood screws, allow for the bot+dock to be fixed in place with the pictured wooden latches. It also acts as an internal hard skeleton for the whole case. There is enough space around all this to shove in my pit equipment (or the insectweights!)

All this is made from 1/2″ plywood, and a quick run on the waterjet or CNC router will take care of it. Assembly will be by wood glue and wood screws. I think it’s a necessary step to prevent disasters if I’m not shipping the robot and equipment down separately.

Exactly two weeks from today! Onwards!

 

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    2 Responses to “Team Test Bot Pre-Dragon*Con 2008 Botgasm, Part 1”

    1. KenneyTh Says:

      Hey, would it be possible for me to buy a few of those switches off of you at Dragon*Con?

    2. the chuxxor Says:

      Remind me some time closer to August 19th so I remember to shove them in my bags…