Various lessons learned from many years of constructing combat robots and other stuff.  Most learned on our very first robot hence some info may be a bit out of date - use at your own risk.

Watch the weight

100Kg's means, in Robot Wars terms, 100Kg's.  We pared everything to a minimum, drilled several hundred holes in the chassis (and don't under-estimate how boring this gets), had our motors re-engineered to remove iron, replaced big servos with little servos, replaced bearings with bushes etc. etc. and still we had to miss off aluminium side-bars to get within the weight limit.  Which we eventually hit exactly but some safety margin would have been nice.  And weigh everything since everything weighs something.  Nuts and bolts seem light when holding one in your hand, but multiply by the dozens used in construction and they count.  And paint weighs, especially when applied using trowels by enthusiastic offspring...

Hint:  we weighed robots at the local sand-quarry who have a very accurate set (+/- 0.2Kg) of sack-scales.  A weighbridge, by comparison, is +/- 20Kg...

DisConstructor: although we still had to watch the weight, using a titanium monocoque meant no chassis, hence weight saving. Moving to Nicad's saved another 3Kg too, although this is a very expensive way to diet. And I didn't let the kids paint the robot this time!

Rivets are stronger than screws

One mistake we made was to fasten the titanium shell using self-tapping screws.  As the chassis was 18swg steel tubing, there was precious little thread being cut.  The resultant damage (thanks Shunt) was a twisted chassis as we weren't getting the benefit of structural reinforcement by the titanium as the screws had popped.  Rivets, which were the intention until time ran out, would have probably prevented this.

Radio reception

This, or rather lack of it, was a real b***ard in Wembley Arena.  We'd gone for using the chassis as an aerial - not a good idea in hindsight.  Although we didn't totally lose reception, there was a lag between moving the r/c joystick and Doris responding.  Hence, more time than we wanted being barbecued on the flame-pit.

Subsequently we have found a web-site www.buildbots.com/talulah/radio  (or alternatively try http://homepages.which.net/~paul.hills/Radio )which has copious technical details and shows the only apparent UK source of decent 40MHz aerials (www.quickuk.co.uk) .  (It also shows a neat solution for a twin-aerial installation).

DisConstructor: We use the Paul Hills twin-aerial setup and it is very effective. Aerials made from piano wire with several layers of heat-shrink tubing. The base-loading coil was wound by bending the piano wire around a 5mm former (drill-bit shank) with assistance of a blow-torch.

Practise driving the darn thing

May seem obvious but put in some practice. Ours comprised racing Doris around a car-park the week before the auditions, then spending the next day mending the drive-chains.  This wasn't enough!!!  There was no opportunity for target-practice.  So, coupled with the radio reception problems, lambs to the slaughter...

Titanium isn’t the answer to everything

Titanium, though weight-for-weight is four times stronger than steel, isn't the Holy Grail of robot construction.  Thin titanium is almost as easy to puncture as thin steel (witness two large holes made with consummate ease in Doris by Shunt).  And thin titanium bends just as easily as this steel (witness our titanium side panels which bent into the tyres on one side, jamming the wheel.  The intention had been to use 6mm aluminium but that 100Kg weight limit imposed itself again...).  

Bending titanium involved forming between two large flat aluminium bars with a large hammer.  Cutting titanium sheet can be fun;  avoid grinding it (dust can be explosive), use a coarse blade on a jigsaw (fine ones clog almost instantly) and plenty of water.  We used air-powered shears which struggled occasionally even though the sheet thickness was only 0.9mm.  Drilling titanium wasn't too much of a problem providing the drill-bits were sharp.

For the masochistic or financially loaded, welding titanium is apparently not too bad so long as the right sort of TIG gear is used.  There's a good source of info, including a downloadable manual on every welding technique imaginable, at www.titaniuminfogroup.co.uk

DisConstructor: 0.9mm Ti may not be much use but 5mm Grade 2 is ace. The shell and top/bottom of the disk is made from the stuff. Yes a couple of robots have got through it but not to any great extent. Welding...see under Suppliers. Cutting - had some laser-cut and some water-jet cut. Avoid laser-cutting if intention is to weld it as the oxide coating (caused by laser heat) needs to be ground away to avoid weld contamination.

Building takes a lot of time

From initial design to the final built version (via five prototype chassis) took about eight months of most weekends and several evenings each week.  And the total cost increases as flowers and holidays are bought to placate the family.

Don’t over-complicate (and use a PC)

Simple means more reliable and faster to repair.  Doris' drive-chain was based on go-kart axles, bearings, chains, and hubs.  Driving three wheels per side was fine on the bench but on test runs we had huge problems keeping the drive-chains on.  So (three days before the auditions), we took the drive-chains off one wheel per side which solved the problem and reduced the weight with no noticeable performance degradation.

And if you can, design the thing on a PC so you can be more or less sure everything fits.  (We used Visio 2000 which was ok for a 2D drawing package)

Watch the welding

Heat, whether from gas or electric welding, distorts.  Extensive use of a lump-hammer was required to restore our chassis to the flat, square shape it was intended to be.  MIG welding is kinder than stick welding, which in turn is much kinder than gas welding.

Watch the ground clearance

No point in trying to skim the arena floor by a mere hair's breadth - anything which wants to get underneath you to flip will do so.  Our ground clearance was intended to be 1/2-inch but was reduced as no allowance had been made in the design stage for three thicknesses of titanium plus the heads of the self-tapping screws used to fasten it.

Get a grip

Using pneumatic slick go-kart tyres gave tremendous grip in a concrete car-park but s*d-all in the arena.  Not helped by having to over-inflate them to compensate for the reduced ground-clearance.

DisConstructor: Found this excellent place which cuts treads into go-kart slicks. Made big difference. See under Suppliers. DisConstructor's tyres were slightly under-inflated.

Have fun

Building a robot is fun, fighting (despite the ratio of build time to battle time, despite the damage caused by competitors, stationery objects, and some dodgy driving, despite the physical effort of lugging around a 16-stone dead weight), is even more fun.  Try it