Design criteria
To design and build a tracked robot with a weapon based on a lifting device.
Current specifications
Dimensions: L: 820mm x W: 500mm x H: 155mm
Motors: 3 x Philips/Sinclair C5 motors 2 for drive and 1 for the weapon system. Motors weigh 3Kg and are 150mm x 100mm x 100mm excluding the gearbox.
Batteries: 2 x Yuasa 12v, 18ah generating 24v when wired in paralell.
Speed controllers: 2 x 4QD NCC-60-24, that’s NCC series, standard current 60 amps and 24 volts DC. The aluminium diecast case is 187mm x 118mm x 55mm, the board and case weight about 1.250Kg.
A brief history of the design (OK not so brief)
The design originally was a tracked or wheeled entry with an axe for a weapon, which would be fitter with a special blade. A penetrator which would have a very small contact area unlike Mortis or KillerHertz who have large axe heads. The design quickly evolved and I found 3 axes would be better than 1. 2 axes would come out of the sides of the robot clamping the opponent while a third could strike the top relentlessly.
Of course the problems in a design like this were immense, trying to move all 3 axe arms far enough with pistons was impossible so I tried motors but this too proved too hard because of the weight, space and cost. So I altered the design a little and adopted a "Vlad the Impaler" type of lifting device (2 lifting forks) with a hammer or axe, that would strike between the lifting poles beating the hell out of the opponent while he was held in the air.
By now I had really started to pay attention to weight, realising the immense weight of the batteries, motors, chassis and armour. I was unable to justify the need for 2 weapons, the lifting device and hammer/axe. (The BBC has no problems with this I see). So I sat down and asked myself which one would be more effective and which weapon wouldn't. Straight away I realised the lifting device would be more likely to immobilise an opponent by tipping them over than an axe/hammer would ever be by trying to immobilise the opposition by destroying there robot.
From then on I kept the "Vlad the Impaler" lifting device until recently when I visited a couple of Robot Wars sites that made me change my mind. Why have 2 lifting poles or spikes when 1 would be able to cause more impact on ramming. If you ram a target with 2 spikes 1 will hit the target first, say left meaning all the weight on the right will want to push forward swinging the robot round. But if you have 1 spike mounted centrally this will not happen.
Getting hold of the right components
From then on I kept the lifting device/ramming spike/axe and worked on all the other stuff like the motors for one. I'd been so busy thinking about the weapon I hadn't thought about the motors and all the other things. At first I tried getting motor companies like Bosch, Black & Decker and Hitachi to sponsor me because they had sponsored other teams. B & D was a waste of time, half the time I phoned up I had to wait 10 minutes just for them to pick up the phone (OK a bit exaggerated, only a bit though), the other half I got cut off. I can't quite remember what happened with Bosch and Hitachi, but in the end I decided to buy my own motors.
I quickly found that car starter motors weren't really worth buying, no disrespect to car starter motors. They might be cheap but there not really meant for Robot Wars. Come to think of it none of this stuff is, but who cares about that. Next I looked at wheelchair motors, these make up the bulk of robot motors in Robot Wars. Easy to come by second hand, powerful enough although a little slow and the gear box and wheels are normally attached directly to the motor, making them easy to install. I'd already got a set of these from an old wheelchair lying round in the shed and yes I do know that’s a strange thing to have in your shed. This included the controller and the two front wheels. The wheels didn't have much grip and the controller would have needed a servo set-up so I could control it using a remote transmitter. I don't like this practice myself, I know people who have done it and liked it but it’s not for me.
As soon as I could I tried these 2 x 12v motors only to find they wouldn't work, this might be because they were over 20 years old and hadn't been used in a long time. I opened 1 up and found that the brushes were no good, d'oh. What now, I knew someone who I thought could help a mechanic turned electrician. But to no avail, they were just no good.
He did suggest I use windscreen wiper motors, I said no way of course and we know what happened to Peister De Resistance who did. In the end I looked at the list of suppliers I had from Robot Wars, at the top of the list I found Adam Harper. Last supplier and repairer of the Sinclair C5, for a good price of £120 I could get motors. Robot Wars contestants received a 25% discount, reducing the cost to £90. Unfortunately since January 1999 the price has gone back to £120 because there have been so many contestants buying them. These motors are powerful, fast, robust, efficient and can be bought with a 5:1 gearbox. Unlike most wheelchair motors the output isn't at 90o making them exactly the right length and width for my design. The motors have 2 outputs which is good for designs that don't want to use tank style steering with 2 motors and only use 1 like car steering.
Unfortunately the gear output on the gearbox is made of Nylon which is quiet and strong but not as strong as steel, which is what I would prefer. Even if you did buy these motors you don't need to use these gearboxes and even if you wanted to you can't, I just bought the last 3 unused gearboxes in the world, ha ha. You can buy second hand gearboxes but they’re not as good as the new ones, as you would expect of course. There are only a few of these motors left, so if you want to buy good motors that aren't cheap then, E-mail me and I'll send you his number.
An ice age later I started to think about the chassis and armour. All the engineering was quite easy and I had someone lined up to do the welding. At first I was going to use Dexion which is strong, cheap and easily to come by, brand new or second hand. But alas a bit to strong, in the end I decided to go for aluminium angle 19mm x 19mm x 3mm x 4000mm costing about £7 per lengh, of which I bought three. The armour is also aluminium which is 3mm thick. The areas where impact is more likely (front and rear panels) are going to be twice as thick making them 6mm. But if I had the money I think I would prefer to go for Kevlar, Carbon Fibre, Lexan or UHDPE because they are all light and strong.
As long as I have the chassis made of aluminium the armour isn't a problem, although I would prefer to use plastic or fibres because they are better against kinetic energy weapons like axes and hammers, these are the weapons you have to worry about because they are so destructive. A cutting disc or chain saw has to keep cutting the same spot for a time to cut through plastic or metal, so that’s no problem its just robots like Mortis, Killertron and KillerHurtz that worry me. One lucky hit and your is out of the running, a great example of this was when Behemoth (that's my mate’s robot) fought Killertron. Killertron did little damage all through the bout then all of a sudden hit a weak spot, the axe went right through a plastic panel hitting one of the batteries. I was there I couldn't believe it, what luck.
To be continued...
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