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Unskinny Bot: 3-lb Horizontal Spinner Combat Robot

Feature wishlist and design constraints

  • Horizontal spinner weapon (my take on bots like Robo-Rooter, Misdirected Aggression, and Last Rites)
  • Belt-driven wheels (not direct-drive; this is to isolate the motors from impact force on wheels from, e.g., another spinner or from fall/toss damage)
  • Slip-belt-driven spinner (slip helps protect the weapon motor from stalling and burning out)
  • Milled armor; each piece must be within an 11"x4.5" millable area due to the limitations of the milling machine I'll be using.
  • Minimize in-shop time.  (I have a 4-month old, so I have very little time for construction right now.  Design for CNC milling on fabricated parts and off-the-shelf parts wherever possible.)
  • Power switch (I always forget this one until the last minute!)
  • Field-serviceable:
    • ability to quickly swap battery (or at least have easy access for in-place charging)
    • wheels and belts easily replaced if damaged/destroyed
  • If time and weight allows, allow easy swapping of weapon blade for a saw blade.

Dragon Con 2013 Microbattles

posted Sep 3, 2013, 5:36 AM by Lewis Baumstark   [ updated Sep 3, 2013, 6:15 AM ]

Sometimes it's all about how the brackets are seeded, and this time fate was against me.  In my first round I was paired with an excellently built horizontal spinner called Stability Margin.  I got chewed up pretty badly, so much so that, in our second round, I had to tap out because neither my weapon nor my drive system would spin.  It was a single-elimination competition this year, so I was out (until the Rumble!).

Damage included:
  • Weapon blade timing pulley is a complete loss.  It apparently was at the right height for him to get under my blade and take out the pulley and belt.  Also worth noting is he somehow managed to remove the lower bushing from the shaft, which is pretty impressive considering the shaft was capped at both ends...
  • Severed both drive ESC signal cables, which of course is why I ended up dead in the water.  I was counting on my weapon protecting the front of the bot, where the ESCs were tucked.  Once that was gone, he got a direct hit on the ESCs through my UHMW armor.  Some frantic soldering repaired this.
  • Wheel armor torn completely up.  But they saved the wheels.
  • From memory I know I have some bent frame from a vertical spinner in the Rumble.  I think it can be bent back, but I need to investigate more.
So ideas for future improvements:
  • Protection for weapon drive.  I may even consider an undercutting blade if I can make the live shaft magic work.
  • Better ESC cable protection.  Probably if they hadn't been so close to the edge of the UHMW they would have been OK.
  • Keep the same wheel guards, but make spares!
  • Design and mill a ring spinner out of a tool steel.
  • More powerful weapon motor, possibly one where the belt can wrap around the outrunner shell instead of using a driven pulley.
  • Offset the weapon motor if possible.  There's no reason it must be centered, and locating it to the side might free up some internal space.
  • Lower profile: use narrower UHMW if at all possible.

Build Complete: New Name, New Instructable

posted Aug 14, 2013, 6:37 AM by Lewis Baumstark   [ updated Aug 14, 2013, 6:37 AM ]

Not many updates here lately; been too busy building it.  :)  As the subject says, it's finished; the Instructable for it is now live and, as of this writing, is featured on the main page (click through for larger version):

You'll also note that I've changed the name from the working one.  Turns out there is at least one reference to "Beau Pummel" on the Internet already...and it's a reference to domestic abuse.  I don't want to be associated with that or make light of it, so I came up with a better, moar awesome name: "Unskinny Bot".  If you don't get the reference, you aren't a child of the 80s/early 90s.  And your musical education is incomplete.

Parts List

posted Feb 16, 2013, 10:50 AM by Lewis Baumstark   [ updated Feb 17, 2013, 9:02 AM ]

Just finished ordering about 95% of the parts I didn't already have on hand.  Here's the parts list so far:




Drive pulley4FingerTech 15T timing pulley 
Weapon motor pulley*FingerTech 16T timing pulley 
Weapon blade pulley *FingerTech 42T timing pulley 
Power switchFingerTech power switch 
Weapon belt *FingerTech 100T timing belt 
Drive beltFingerTech 43T timing belt 
Weapon motorTurnigy Park300 1600kv brushless outrunner motor 
Weapon ESC F-30A/15205 Hobby King 30A ESC 3A UBEC
Motor mounts Kitbots B16 motor mounts (pkg of 2) 
Weapon shaft bearings3/8" ID needle roller bearings, McMaster-Carr p/n:  5905K22
Drive MotorsBeetle B16 Gearmotors 
ReceiverFutaba R2004GF 
Weapon shaft hub 3/8" bore set-screw hub clamps 
Drive motor ESCBanebots bb-3-9 
Wheel1LiteFlite 2-1/2 foam wheel (pkg of 2)
Wheel hubDave's Hubs 4mm bore (pkg of 2) 
Top & bottom armor12"x12"x3/8" Al-6061 plate, McMaster-Carr p/n: 89015K31 
Wheel axle4mm 316-stainless-steel shaft, 200mm long, McMaster-Carr p/n: 1265K37 (enough to make 2 shafts and some spares)
Weapon blade3/8"x2"x36" Al-6061 bar, McMaster-Carr p/n: 8975K593 (enough to make 3 blades) 
Internal bulkheads3 ft3/8"x1-1/4" UHMW bar, McMaster-Carr p/n: 8702K731
Weapon shaft3/8"ODx12" long hardened steel shaft, McMaster-Carr p/n: 6061K32 (enough to make 3+ shafts) 
Armor-to-bulkheads fasteners18-8 stainless steel Plastite screws, 6-19 thread, 3/4" long, 50-count box, McMaster-Carr p/n: 96001A268 

*I'm spec'ing the weapon system using timing belts but the plan is to turn the belts inside-out so they'll be allowed to slip.

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