Construction of 13BLACK
GENERAL DESIGN & LAYOUT
As you will probably have gathered by now - 13 B is an unusual robot in that it is a double spinner. Why this design? Well after the destructive success of Hypnodisk in RWS4, we just had to build some sort of spinner bot.
Our first thoughts were along the lines of a Hypnodisk clone - but Hypnodisk
suffers from being vulnerable at its back end - nobody wants to mess with the
front, but the back is a tempting soft target. We wanted to design out that
weakness from the start.
"Lets protect it with another disk!" was the obvious answer. "Also, if we run them in opposite directions, the gyro forces will tend to balance out, making it more stable" Great idea! Also, the increase in maximum weight for S5 (now 100kg, from 80kg in S4) might allow us to do this - if we were really careful with the design. .
OK - but what about the driving wheels? Hypno has 4 wheel drive - 4 wheels which can get locked up if their mudguards get bent! (Isn't that right Pussy Cat?!) Also, a 4wd drivetrain is heavy and ungainly and would have to live somewhere under the disks making the bot a bit top heavy. No, right from the start it was clear that 13B would need 2wd - but 2 big and very grippy wheels. These would be mounted midway between the disks, and we would use a skid steer system.In theory, if the drive wheels were grippy enough, we wouldn't even need castors at the ends - we could just scrape the chassis on skid plates - as the arena floor is flat.
The chassis is constructed from mild steel, it was originally bolted to a wooden floor frame prior to welding, it has also undergone several modifications since the original design. Here you can see it prior to RW series 6, the `front to side` pieces are the main difference to the series 5 version, also removed are some longitudinal sections in the middle area.
For the drive, each wheel has it`s own Bosch 750 motor running on 24v. This is mounted in slotted 3mm aluminium, the aluminium also holds one side of the wheel. Being direct drive to the wheel means all we have to do is slide the motor into the teeth in the wheel rim as close as possible. The wheel can easily be removed by removing the axle, the motor can then stay in position.
The wheels were a very unusual design - with a double internal row of chain link bushes. The drive motor (a standard Bosch 750) was fitted with a duplex sprocket that engaged inside the rim of the wheel. This gives a direct, positive drive which is extremely compact and will not suffer from chain jumping etc. This meant the wheels had to then be drilled around the inner rim to accept 50 silver steel pins each. These then hold two chain ferrules each, which makes each wheel a total of 151 parts.
After much searching, we settled on using kart racing tyres - super grippy, tough and (very important) endless. Some other competitors have tried bonding rubber strips round wheels, and they invariably peel off at the joint. But quality, soft racing kart tyres are quite big, even the fronts (10" diameter) - so we decided to make some unique wheels to mount them upon. We sliced the sidewalls off the tyres to leave flat, slick treads, then bonded the treads to solid aluminium wheels.
The batteries are Hawker SBS, a big change for series 6 is where they are mounted. Originally fitted flat, under the discs, they are now vertical and in the centre section. This has helped us to reach a fast body spin much quicker as well as giving them more protection. Removal is just possible but they can also be charged in situ.
WEAPONS - MOUNTING
The weapon motors, a single Bosch 750 drives each disc independantly - again on 24v, are mounted in aluminium slots within the Hexlite panels. These slots were CNC machined (see pic). This enabled us to tension the disc drive belts by simply moving the motors.
Each weapon motor drives a spindle, mounted in steel bearings. The upper bearing can be seen in the spindle picture, it has an internal diameter of 50mm, the lower bearings are slightly smaller and are usually fitted to Renault van axles.
After fitting, the spindles are secured using locknuts which are wired on for extra safety.
WEAPONS - DISC CONSTRUCTION
The weapon disks need some strange characteristics - Low weight (because of the robot's weight limit) but high moment of inertia (to store kinetic energy). The disks need to be stiff enough not to deform on repeated impact, but not transmit too much shock back up the drive train (and so wreck the motors etc.) In the end, we settled on a tubular steel rim, with the cutter brackets welded onto the rim, an aluminium hub, with an integral break-away clutch feature, and the space between would be filled with carbon fibre/kevlar composite on styrofoam to give stiffness, toughness at low weight. We decided that bolt-on weapons were best - so we could change them to suit the enemy and in case they got damaged.
This photo shows the assembly of one disk - 5 of the 6 pink styrofoam cores are in place and the double kevlar centre webs (yellow & wet with resin) are bonded to the rim inner ring and the hub flange. The outer faces of the disk were later skinned with many layers of carbon fibre and kevlar then vacuum bagged to consolidate the lay-up.
The disc drops onto the top of the spindle and is lock-nutted in place by the B.F.O. spanner that I made from a water tank immersion spanner.
TO BE CONTINUED........