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12lb Bar Spinner |
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Mildly Impolite is the working name for a new 12lb Bar spinner being designed and built largely by my son Andrew. The name is a tribute to Team Mad Overlords 30lb bot
"Totally Offensive" as it was the inspiration for this design. As some have pointed out it also bears a close resemblance to "Little Yellow Bus" and some other bots, well imitation
is the sincerest form of flattery! It is also the first Bot in which Andrew has done most of the solid modelling. |
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I have found one of the most useful things to do when starting the design of a new bot is to create a spreadsheet to list all the parts required and calcualte the
total weight. The current spreadsheet for Mildly Impolite is
here . |
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The major weakness of Totally Offensive has been warping of the chassis and to in order reduce or prevent this entirely the chassis is designed out of two
large round aluminium tubes welded together. A third smaller tube is welded in place at the front to carry the weapons axle. |
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Bronze flanged bearing are pressed into either end of the small vertical tube and a 1/2" steel axle run through from the top to bottom. Bronze bearings
were chosen after seeing many ball bearings shattered in combat. Both the bearings and the axle are "off the shelf" Mcmaster parts. |
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A Graupner Speed 700, probably the 8.6v Ball bearing version, will provide weapon power. 3mm HTD pulleys and belts will transfer this to the weapon axle with a reduction of 6:1. The blade will
be about 14" long and weigh about 3.3lbs. I will probably use "Trantorque" or similar bushs to attach the big pulley and the weapon blade to their axle. |
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Harbor Freight 7.2v Drill motor/gearboxs
with standard cncbotparts 3" Colsons
will probably be the driveline of choice although 4.8v Handiworks could be used. To provide power for the whole bot a 12v 2600 NiMH Pack will be used. It will need to be a custom design to fit in the main Chassis tube. There is probably space and weight for a higher voltage but at the moment the use of the Mtronik ESC's restrict us to 12v.
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December, 12, 2004 |
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To attach the Weapon to the shaft we will use a "Shaftloc" bush from
SDP-SI
. This has a 1/2" bore and a 3/4" outside diameter. It allows the use of a plain shaft without the built-in weakness of a keyway. |
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This will be combined with an aluminium hub. The hub will have six tapped holes in it and a shoulder to locate the blade. |
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The blade will be fastened to the hub using six countersunk screws. A slightly domed "skid" will be added later over the bottom of the shaftloc
bush and hub to keep the blade up off the arena floor. |
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The blade is 14" long by 2.5" wide and 3/8" thick. This weighs about 3.5lbs. The front to back tube was lengthened slightly and raised
relative to the rear tube to allow adequate clearance for the blade. |
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December 20, 2004 |
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Two Bulkheads made from 3/8" UHMW mount each motor. They will be retained in the rear tube using three screws each. |
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