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madoverlord:robots-offensive [2016/05/14 16:03]
madoverlord
madoverlord:robots-offensive [2016/10/04 14:42]
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-==== Totally Offensive Build Report (Robots) ==== 
- 
-After Anorexia mutated into a lifterbot, 
-the kids started bugging me for a robot of their own, 
-so I started thinking about how to build them a seriously nasty 30lb robot. ​ They clearly wanted 
-something with an active weapon and a simple strategy. 
- 
- 
- 
- 
-My design constraints were that I wanted to make something that would be easy to construct, 
-would reuse a lot of parts I already had (like intercooled battlepacks,​ victors, etc), and would 
-use standard parts for the tricky bits to save time and make the build easier (my time was limited 
-and I only had a few months to be ready for the 
-[[http://​www.steelconflict.com/​|Southwest Divisional Championships]]). 
- 
- 
- 
- 
-What I came up with was a design that's "​totally offensive"​. ​ Everything is sacrificed 
-in favor of the weapons system, a magmotor-powered lawnmower blade. ​ I tried to pare off every 
-ounce I could so that the blade could be as hefty as possible, and it ended up being a 6.9lb 22" 
-hunk of tool steel. 
- 
- 
- 
- 
-By using a lot of standard parts, I figured that if the design wasn't successful, I'd have lots 
-of bits left over to reconfigure into a different layout. ​ As it happened, this turned out to be 
-a fateful decision 
- 
- 
- 
- 
-<​html><​a href="​http://​media.madoverlord.com/​Lg/​DSC022/​DSC02232.JPG"​ target="​_blank"><​img src="​http:/​wiki.animeigo.com/​MO/​Sm/​DSC022/​DSC02232.jpg"></​a></​html>​ 
- 
-The first iteration was a simple squat "​T"​ 
-of aluminum C-channel, aggressively hole-sawed to reduce the weight. ​ The foot of the T mounts 
-the magmotor and Whyachi gearbox underneath, and an intercooled battlepack on top.  Terry of 
-Team Whyachi was nice 
-enough to put a nice radius bevel on the bottom of the gearbox shaft so it could glide around more 
-easily. 
- 
- 
- 
- 
-The arms of the T contained the Victor speed controllers,​ radio, gyro, power switch, 
-and weapons relay (both from Whyachi). 
- 
- 
- 
- 
-Underneath the T were the translational drive wheels, based on Whyachi T-Boxes. ​ I love these things, 
-especially with the [[smalljohnson.t.html|inexpensive Small Johnson motors]]. 
- 
- 
- 
- 
-The drive wheels were set so that they were tangent to the arc of the weapons blade. 
-This means that the bot could easily turn left and right without moving the blade at all, at the 
-cost of having to scrub like nuts to drive forward or backwards. ​ A pushybot this wasn'​t,​ but 
-given the lack of armor on the bot, being able to always put the "​nasty"​ part of the bot towards 
-the enemy was a big plus, I thought. 
- 
- 
- 
- 
-The plastic drainpipe at the back of the robot was the first part of a passive self-righting 
-mechanism. ​ And the black netting was there to basically give some minor protection against flying 
-debris. 
- 
- 
- 
- 
-Two weeks before SDC, however, I started having some serious second thoughts. ​ The problem 
-was that because the hub of the gearbox scraped on the ground, the bot wasn't very manuverable. 
-The askew orientation of the wheels let it turn on a dime, but it often had trouble moving 
-forwards and backwards. 
- 
- 
- 
- 
-<​html><​a href="​http://​media.madoverlord.com/​Lg/​DSC022/​DSC02252.JPG"​ target="​_blank"><​img src="​http:/​wiki.animeigo.com/​MO/​Sm/​DSC022/​DSC02252.jpg"></​a></​html>​ 
-<​html><​a href="​http://​media.madoverlord.com/​Lg/​DSC022/​DSC02267.JPG"​ target="​_blank"><​img src="​http:/​wiki.animeigo.com/​MO/​Sm/​DSC022/​DSC02267.jpg"></​a></​html>​ 
- 
-So I went back to the drawing board and came up 
-with a tilted spinner design, somewhat reminiscient of the lightweight 2EZ.  Worst case, 
-I figured that I'd get some extra practice welding. 
- 
- 
- 
- 
-With one day left before I had to ship the bots to SDC, I got everything together and 
-gently fired it up in the garage. ​ It drove pretty well.  Then I fired up the spinner... and the 
-bot promptly turtled itself! 
- 
- 
- 
- 
-Whups! ​ Because of good old "equal and opposite reaction",​ when the blade started spinning, 
-the robot wanted to turn in the opposite direction, and because the blade was at an angle, this 
-caused the bot to lift up on a ball caster and flip over. 
- 
- 
- 
- 
-Several chunks of garage floor later, some emergency wheelbase widening resulted in a bot 
-that wouldn'​t immediately knock itself out, and into the crate it went. 
- 
- 
- 
- 
-But at SDC, I had problem after problem. ​ The most vexing one was some sort of bizarre 
-interference problem that was locking up my IMX-1 mixers. ​ This actually affected both of my 
-robots! ​ It appears that under certain circumstances the small johnson motors can create a spark 
-whose RFI nukes the IMX-1. ​ So after losing fights because my robots were locking up, I had to 
-reconfigure both of them to use in-radio mixing. 
- 
- 
- 
- 
-But more serious was that Totally Offensive should have been named Totally Suicidal, because 
-every time it hit something, it would flip upside down and lie there helplessly. ​ After one memorable hit 
-it danced its way on its side around the arena. 
- 
- 
- 
- 
-So it was back to the drawing board -- again! 
- 
- 
- 
- 
-<​html><​a href="​http://​media.madoverlord.com/​Lg/​DSC023/​DSC02390.JPG"​ target="​_blank"><​img src="​http:/​wiki.animeigo.com/​MO/​Sm/​DSC023/​DSC02390.jpg"></​a><​a href="​http://​media.madoverlord.com/​Lg/​DSC023/​DSC02394.JPG"​ target="​_blank"><​img src="​http:/​wiki.animeigo.com/​MO/​Sm/​DSC023/​DSC02394.jpg"></​a></​html>​ 
-<​html><​a href="​http://​media.madoverlord.com/​Lg/​DSC023/​DSC02395.JPG"​ target="​_blank"><​img src="​http:/​wiki.animeigo.com/​MO/​Sm/​DSC023/​DSC02395.jpg"></​a><​a href="​http://​media.madoverlord.com/​Lg/​DSC023/​DSC02396.JPG"​ target="​_blank"><​img src="​http:/​wiki.animeigo.com/​MO/​Sm/​DSC023/​DSC02396.jpg"></​a></​html>​ 
-<​html><​a href="​http://​media.madoverlord.com/​Lg/​DSC023/​DSC02392.JPG"​ target="​_blank"><​img src="​http:/​wiki.animeigo.com/​MO/​Sm/​DSC023/​DSC02392.jpg"></​a><​a href="​http://​media.madoverlord.com/​Lg/​DSC023/​DSC02393.JPG"​ target="​_blank"><​img src="​http:/​wiki.animeigo.com/​MO/​Sm/​DSC023/​DSC02393.jpg"></​a></​html>​ 
- 
-This time I came up with a simplified version of 
-the original undercutter design. ​ The drive wheels are exactly in line with the spinner hub, 
-so I can rotate around that axis while still having full forward and backward drive without 
-scrubbing the wheels. ​ The frame is made out of T-angle with some minor lightening holes. 
- 
- 
- 
- 
-Underneath the curved UHMW bonnet are all the electronics and the battery. ​ The radio is 
-mounted under the battery in a compartment formed by some UHMW and the bottom of the T-angle 
-members. ​ The Victor speed controllers are located between the battery and the magmotor. ​ At the 
-rear of the robot is a single ball-caster,​ so the frame is tripod-supported on the caster and the 
-two drive wheels. ​ This means that the blade is suspended off the arena floor and the blade tip 
-height can be adjusted a bit by adjusting the length of the ball-caster support. 
- 
- 
- 
- 
-There are a several cute design features that I came up with.  First, I noticed that the 
-motor mount screw access holes in the T-box were just the right size to be tapped for a 9/16-18 
-bolt.  So I did that and used it to make the motor mountings more sturdy. 
- 
- 
- 
- 
-Next, I mounted the C1 contactor that powers the Magmotor on top of the gearbox! 
-Yeah, it sounds stupid, but it solved a space problem, reduced the frame size, the two bolts I installed to support 
-the UHMW bonnet protect it from incidental impacts (as does the bonnet), and it's far enough out 
-of the way that I'm not too worried about direct damage, only about impacts caused when the bot gets 
-flipped or tossed. ​ If I have the time and the weight I'll add front and back UHMW covers for some 
-added protection. 
- 
- 
- 
- 
-Finally, I dispensed with the power switch entirely, and now activate main power by clicking together 
-some powerpoles and making them secure with a ziptie. ​ Saved me a few precious ounces. 
- 
- 
- 
- 
-At which point, it was back into the garage and... it doesn'​t kill itself! ​ Yeah!  It drives 
-pretty well, spinup only causes a 10-15 degree turn, and it seems to be stable. ​ Spinup to about 80% 
-of max speed takes about a second! 
- 
- 
- 
- 
-Who knows, perhaps third time's a charm! 
- 
- 
- 
- 
-**Update**: Totally Offensive went 5-0 with 4 KOs in its first tournament, qualifying 
-for Nationals. ​ In the second tournament, it went 3-2, and we discovered some flaws in the design, 
-so we've redesigned it yet again. 
- 
- 
- 
-