Nuclear Kitten 5 and Pop Quiz 2: Final Update

Sunday, August 31st, 2008 @ 4:31 | Bots, Nuclear Kitten 5, Pop Quiz 2, Project Build Reports

I got a new camera.

It won the features-and-price contest for having a full manual control mode, like a micro-DSLR, which I felt was worth the extra pile of change. However, the vast majority of the time I’ll be using it on dumb point-and-shoot mode anyway. Regardless, this means REAL PICS!

Robot Microbattles is TODAY! Nuclear Kitten and Pop Quiz are ready. They’ve been ready, but I have been making random little changes to make their operation more reliable. Since build reports stop at the competition, this will be the final report for both bots.

Nuclear Kitten 5

I’ve been hitting random objects with NK to test its durability and driveability. So far, it has passed on all accounts. NK has historically been my most successful bot, so I hope I’ve passed the reliability onto this build to let it continue.

I made a change to the drivetrain in the form of getting rid of the timing belts. While having synchronous belt drive made the bot handle that much smoother, they also transmitted shock through the drivetrain much better. On a good impact, the recoil of the weapon would throw the bot backwards. It used to be that the O-ring belt drive of NK4 would absorb this impact, but the timing belt translated this into a violent torque impulse at the drive motor.

The result was that I blew out the left side drive gearbox. After frantically ordering a replacement set and having it 3-day delivered, I decided to bring back the O-ring drive, just running on the timing pulleys instead.

These are square-profile BUNA o-rings from McMaster. I selected a loop that was a full inch shorter than the circumference of the timing belts in order to allow the O-rings to stretch – without this stretch, they will not grip the pulleys.

This works extremely well. The bot still handles like a 4WD, but no further impacts have affected the drive motors. The motors are even more isolated from shock than NK4, since the weapon pod is floating.

And so with this revision, here is the final finished pic of NK5.

Pop Quiz 2

If I learned anything from this build, it’s that the new 2.4Ghz RC systems rock. Both NK and Uberclocker run them, and I have no issues with reception, signal loss, or range, at all. Pop Quiz is the complete opposite of that.

It uses a 75mhz GWS micro-receiver, designed for use in tiny indoor and park R/C airplanes. This means it really doesn’t have much in terms of noise rejection or good filtering, nor that much gain. Throw it from the environment of a balsa wood airplane with at most a few servos and one prop motor and into a tiny confined space, antenna trimmed, surrounded by both sides by conductive ground planes, with 4 high-current open-frame DC motors and 3 high-speed switching ESCs, and there are problems.

The bot is completely undriveable with the weapon on (Oh, did I mention the ring of spinning permanent magnets and a big metal twirly thing?). I actually can’t predict which direction it will take off in when I move the stick. I only have the ability to declare that movement is needed.

So PQ is semi-autonomous in the drivetrain. Hopefully I can emulate controlled movement enough to not get counted out. The weapon works great, and should bounce it around enough to not need controlled movement.

I lost one drive motor in testing to a thrown winding (Not a gearbox failure like I suspected any failure would be). I didn’t bring spares, and these are not motors you can run into RadioShack and get. Fail.

So I had to cut it out of the bot. This front wheel will probably be taped over with cellophane tape to give it more slip. Fortunately PQ2 is 4WD and I have three more motors. It actually handled better with this motor gone.

When all was said and done, I squished everything back in and closed the top. Here’s Pop Quiz 2.0.

Yes, the blade hits at the 3/4 mark of a quarter (about 18 and a half cents). It’s actually raised about 1/16″ higher than the design by fiber clutch washers which I put in to avoid metal-on-metal grinding. I will leave it this way, since .6875 is good enough, and it gives more top clearance to prevent disaster.

I leave for Microbattles in 5 hours.



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