Morris-y-Gwynt ~ beneath the polycarbonate

As promised here are some more pictures of Morris-y-Gwynt and a few notes which I hope may be helpful for other RobotBuilders working towards either Rex's Robot Challenge 2003 or other feather weight competitions.

Most of the photographs have been taken from very square angles to help builders who want to scale dimensions from the pictures. To give some idea of size the wheels are 150 mm in diameter. The weight in full combat gear is just a shade under 12 kg. The front prongs and a vicious steel spike (not fitted in most of the photographs) make up about 3.5 kg of the final weight. The weapons were removed for the obstacle course.

This publicity shot shows the complete robot and the Winner's trophy. We wanted to give the robot a dragon-like appearance to establish its Welsh origin. The name Morris-y-Gwynt translates as Morris the Wind, a character in a Welsh nursery rhyme.

This elevation view gives some idea of the construction techniques used. The motors were bolted to 3 mm thick steel plates which were in turn fastened to the ends of a section of 5 mm wall thickness steel pipe. The pipe (painted workshop grey in the pictures) had been cut in half lengthways to for the main structural element of the robot. This heavy steel structure gave the robot great rigidity and concentrated the mass in the right place between the driving wheels.

The rest of the bodywork was made up of thin section steel angle. Normal commercial angle iron is too heavy. The angles used here were cut from  square tube (about 18 gauge wall thickness in the old measure). This is a tricky hacksawing job, but the end results justify the hassle of cutting the tube across its diagonal. (Hint ~ put the blade in the saw at 90 degrees to the normal position)

The steel angle was bolted and pop-riveted together. To complete the bodywork 4 mm thick polycarbonate sheet was riveted to the inside of the angles. In general, M4 and M6 Allan cap screws were used in the construction. If we were doing it again we would not use the pop-rivets, as these tend to act as local stress-raiser on the polycarbonate. The 'flecks' on the side armour and wheel hubs were the result of a sustained attack from a robot called WEDGE.

This is a front view of Morris-y-Gwynt. The grey painted steel pipe is clearly shown. The front prongs are held in place by 6 x  M6 Allen bolts. Nylock nuts were used throughout the construction. The two front castor wheels (black in between the prongs) were designed to stop the prongs digging into the arena floor in the event of getting the prongs underneath an opponent. In practice the prongs worked as a battering ram rather than as a wedge for getting under the sides of other robots.

This is the rear castor. It was added as an after thought. The original design just dragged its tail along the arena floor, but this caused too much friction and wore the rivets off the base. The long protruding lengths of thread were used to fix the rear spike, so its not that we couldn't be bothered to cut them down to the correct 1.5 threads clear of the nuts. Note the lightening holes, these give a handy grip to pick the robot up by. The bracket was cut from a piece of steel box section and is welded to the rear member. This bit has to be quiet tough as it takes a fair amount of battering in the arena.
 

This plan view shows the layout of the main components. It is the most compact way of putting the motors and batteries together.

Big Tip ~ Aerials. They need to be outside. We put our aerial inside a piece of stiff plastic tube that stuck out of the top of the bodywork about 3 ft. It looks awful, but it works. You will not get adequate radio reception with the aerial (the thin grey wire) coiled up inside the casing.  I would guess that this is the problem with lots of Rex's Robots that don't seem to go properly. Another Big Tip ~ don't point your transmitter aerial at your robot. Keep the transmitter aerial a near to vertical as possible. The signal is weakest looking along the axis of a whip aerial.

This shows the electronics. The radio receiver is wedged between the lefthand side and the No. 1 battery by a piece of closed cell packing foam. The batteries are held in place by heavy cable ties. The electronics are to Ian Swann's design. We brought the components and soldered up the boards ourselves. I would recommend doing it this way, because then you will feel confident enough to troubleshoot things when they don't work or if you have to replace a MOSFET. We have avoided connectors as far as possible preferring to solder flexible multistrand cables between boards. The last thing you want is a connector coming apart in a battle.

Yet another Big Tip ~ Use hot melt glue to stick battery connectors to the terminals. You don't want these to come apart in the middle of a melee.

The electronics were mounted on a piece of blue acrylic. This was to enable our only speed controller to be swapped between Morris-y-Gwynt and the ill-fated SPARKY. With hindsight this plastic was a bad choice, much too brittle. We would use 4 mm polycarbonate in the future. The 9V supply comes from a pack of AA cells. Note the use of lots of hot melt glue to fix the battery pack down. These battery holders are not too clever. The plastic tends to creep under the constant force exerted by the contact springs causing the ends to splay open and the batteries to become loose. It would be a good idea to take the batteries out if you were going to store the robot for any length of time. (Bit of a problem if you have glued the battery pack down with hot melt).

This shows the heavy cable soldered directly to the brass brush holders on the stator plate of the motors. The cable is 3 mm2 copper. The motors have had minimal modification, as shown in the Real Robots magazine (not the most recently described mod where Rex shows you how to match a pair of motors) The fixing lugs were shortened to get as much clear shaft protruding from the side of the robot as possible.

The blue wheels (Guitel, as used on Razer) were mounted on turned steel bushes. The bushes were a tight fit on the 10 mm output shaft of the motors and were held in place by 3 mm roll pins. Phosphor-bronze washers were turned to exact thickness to give 0.003" of free play between the steel bush and the gearbox casing. This is important to get right as otherwise the gearboxes are very noisy when you reverse the motors.

We hope that these pictures will give you some idea of how we did it, as you can see its not much like the one in the magazine. The most expensive parts were the speed controller and the remote control gear. Most of the other stuff was either donated or was genuine scrap. Our parting advice is that reliability won the 2002 event, in 2003 you will need more than just reliability, you will need an effective weapons system to win next time.