Click to enlarge pre-combat image

My very first Critter for the Denver Mad Scientists annual critter crunch. Black dog took a lucky 3rd place in the 2001, 2 lb class, he was slow and lacked great maneuverability, but driving skill and a wickedly maneuverable lifting arm made the difference.

Click here to read more about Black Dog 1,...

Now Black Dog is in a new city and undergoing quite a bit of re-design to compete in what seems to be a tougher level of competition that's developed over the years Iv been away from robot combat, and a different weight class to boot. This old 2 lb critter (1.6 lbs w/.4 lbs dead weight added) will be down sized to compete in the 1 lb class here in Seattle. Almost every part of this critter will be tweaked, re-worked or upgraded. Mind you, i have no delusions of grandeur for my first time back out, I am taking it easy by re working this design with parts I mostly already have on hand. I doubt ill win, or even come close, I just want to have fun and survive through out the day while learning about the local competition.

The de-construction begins:

After 6 years in a box this is all that's left of Black dog, it was chewed up pretty badly when I ran it into a 20lber for kicks at a practice session, after that it went into storage. I had originally considered re building it structurally, just to have as a mantle piece dust collector, but this total rebuild will be much more fun.

First things first, Black dog used a some what unique steering method, unlike most of today's "tank drive" designs it employed a single drive axel, and a servo controlled steering mechanism similar to hydraulic construction land movers.

This method was useful in some ways but wasteful in others. It relied on the single steering wheel having enough traction to dig in and re direct the vehicle. and the steering linkage that ran below the bot was off center and had to be quite powerful to pull the body left and right. in addition the center pin used in the design for the body to pivot on was strong but weighed in at .4 oz alone. while i was often able to get the lifting arm under another critter and use its mass to help the steering wheel dig in, when i did not have a critter in my grip, i was often out maneuvered due to a large turning radius. This entire package is getting thrown out the door and the critter is going to be turned around, the wide flat wedge in back will now be the front and the lifting arm will be flipped around to face that direction,.. this bot will still have a single drive shaft but the steering will now sit directly below the servo connected directly to the servo horn and be made out of an extremely grippy rubber wheel from a printer, if all goes well, this bot will have nearly the turning radius of a twin drive system, with all the power coming from a single (larger) motor and gear box.

Cracking open the shell I was reminded of just how silly I was when building this first bot,.. originally I had constructed the shell out of 4 pieces of aluminum cut individually and then epoxy back together to form the clam shell,.. nothing else was holding these seams together,.. just some old brittle epoxy, apparently that was enough back then,.. but with the re design the clam shell will be a single piece of metal cut and then bent to form the shell, and then the two seams will be bolted together using a UHMW scab under the shell.

Looking closer you can see some other interesting decisions. Starting with the drive system, first off you see the hacked servo controller board. I frequently used these as light weight speed controls with reverse, because back then there where not as many options as we have today for small light weight speed controls that could handle a few amps and had reverse. this Item will be replaced with one of the many robot speed controllers on the market that are designed for even more output. continuing on the drive train, the worm drive gear box had tons more torque than could ever be transferred to the ground by 2 lbs of weight, and was woefully slow. This gear box will also be replaced, probably by one of my high speed tamaya gearboxes that I have modified to accept a larger motor and a metal pinion gear. Finally, the last bit of the drive train, the tiers which where sand paper covered for grip on a wood fighting surface, will be replaced by ultra grippy rubber tiers.

Here you can see the Gearbox and speed controller removed to show the bare base plate with nothing but the steering servo, which will be downsized and re located to the new back of the bot. the old aluminum plate will be used for first round testing of the new system, but then replaced in final re build with garolight of carbon fiber.

The old gear box was 3.30 oz and was useless,. one of the new potential gear boxes is 4 times faster and still has more torque than i could possibly transfer to the ground tanks to an upgrade to a specially tuned motor made for higher performance that the standard motor these gear boxes come with. at 2.20 oz its a feather weight with a lot of punch. One other option i have is a tamaya HP gear box,.. its even faster, still has plenty of torque, but weighs in at about 3.6 oz,.. ill have to do some testing before i settle in on one of these options or look to other options altogether.

And last but certainly not least the 2 axis lifting shovel. weighing in at 10.25 oz (6.10 + 4.15 see second photo) will be completely re designed.

So far I have planed to replace the horizontal servo with one that weighs in at half the weight but the same torque and speed, and the vertical servo with one a little less heavy, but nearly twice as strong, and just a hair slower.

The old brass shaft arm will be replaced with a carbon fiber rod and the shovel itself will be interchangeable depending on the battle. the arm will mount directly onto the servo hub saving a lot of weight from all the linking hardware that was needed with the old design. In addition the servos will be powered directly off of the batteries (over volting them) working around the limitations of the BEC. Considering that this arm had the power to lift 2 lbs with half the torque and a few less volts,.. im highly interested in how it will interact now with a 1 lb critter. I am also designing the arm to bend/give quite a bit to help lessen the initial impact of high mass spinning devices.

I also plan on moving from the original 4 AA 4.8v 1100 mah pack to a 5 AAA cell 6v 1000 mah pack, this time placing the batteries below deck between the drive and steering wheels. The entier upper arm assembly will be packaged in a UHMW protective shell.

So far I have shaved off more weight than I needed to while upgrading every performance stat, which will allow me to push armor and drive train to a higher level than I was thinking,.. Which is a good thing,.. very, very good,..

The re build: > (comming soon)