Rules on use of Axe

Paul the biggest piece of advice I can give you is to stay away from IC engines unless you have ALOT of experience with them and even think long and hard about using them.

To compress a spring you are going to want a lot of torque. At low revs an IC engine just does not have a huge amount of torque. It gets this around the 2/3 rpm range which means you need a clutch. You will also need to be able to start it from inside the arena without touching it incase the engine stalls in battle (and believe me it will do). This means an electric starter which is adding more complexity to the design.

Electric motor, far few working parts to go wrong, it has all its torque at lows revs (where you want it) and they are generally cheaper and easier to maintain.

The biggest headache I had when on robot wars was the petrol engine we used in typhoon 2 to spin the disc. Dont me get wrong, there are nice advantages such as being able to have a seperate energy source for the weapon and your fuel not counting in the weight limit but then you also have to consider if the events you will enter will be able to run an IC engine. A lot of indoor events cant.

Ok I have waffled a bit but hopefully you can pick out some nuggets from all the waffle.

Thanks for all your comments, especially Gary. I watched some stuff on youtube of the competitions and was thinking, that could be more spectacular with flying pieces of robots all over around. At the opposite, even if it is possible to construct a destructive robot I had in mind, a lot of effort of your fellow competitors is undone in three minutes. Can I expect a certain level of respect for the bots, like not totally destroy your enemy robot?

For the IC engine, I can imagine it will be though, but many hurdles have been overcome right? As long as the engine - with sufficient cushioning - can bear the blows and it keeps running turned upside down, how many more problems can you expect?
Besides to start with, isnt it relatively easy to implement a cross bike engine with clutches? After all, all is set and done.

The electric engine is much easier indeed, but with increasing power, the costs will rise proportional (maybe even exponential).

Dont worry Paul. Build it. A bit of damage is no problem. And in modern day events, no robots are trashed. You can expect a high level of respect for robots and Roboteers.

Paul , I had a 250CC adapted crossbike engine around in 2002. Its 12 kg, with the gearbox milled off. Without starter motor.And that was watercooled. An aircooled model (obsolete now) is even heavier. Youll need a Tillotson or Walbro diafragma carb to work in any position- normal floater carbs are very fickle about that-

But I ask only 1 question. How are you going to lock the axe against the power of the spring?

Paul if you wish to go for an IC engine then I wish you all best but I would still advise against :)

Dont worry about people destroying your machine. I have a rule when it comes to fighting in the arena, if my opponent is still moving then he is still fair game, if he has stopped then I stop. Most roboteers follow a similar unwritten rule.

Ok, destructing the other bot doesnt seem like a problem to me anymore, as long as I stop when the other bot doesnt move anymore.

Second, will the weight cause any trouble? Say the total engine will take 40 kg, there is still 60 left for armour, the weapon (axe, hammer, etc) and other stuff.

Does anyone know something about the limitations of an IC engine? Think of what happens when the bot and therefore its engine is turned upside down - not uncommon with all those flipping bots. What is a reasonable thickness of what kind of steel for the armour, protecting the IC engine? Further I am concerned about the volume the engine with all its side parts will demand.

I agree on the IC engine advice, it is not worth the bother and goes against the KISS principle. Plus there will be a lot of events where you couldnt compete since they are indoors and most venues dont allow IC engines there.

Paul you are going to struggle to fit in any single component weighing 40kg into a 100kg machine. Believe me when I say that 60kg will not be enough for the rest of the machine.

I struggle to fit single motors into my machines that weigh 15% of the total weight whilst giving enough weight to other components.

For 10kg you could look at using an etek motor (http://www.robotmarketplace.com/products/ETK-ETEKRT.htmlhttp://www.robotmarketplace.com/prod...TK-ETEKRT.html) or something on a similar scale. Huge amounts of torque, all you would need is a gearing and locking mechanism.

I am not saying that this is the route to take but if you look above there is no one saying the IC engine is a good route to take and there is a reason that there are no active robots that I know of that use them.

Following your advice would probably be the best, but maybe I have to experience it myself. Does anyone has some building plan about a robot with a IC engine and its limitations (e.g. weight, torque etc)?

How much does a ETEK motor produce compared to a typical IC engine? For example how much HP does a 250 cc produce compared to the ETEK motor from the site.

Comparing an Etec to a smallish IC motor

A good tuned 2stroke 250CC does easely 25Hp. But will run up to 20Krpm to get it. Weight, after adaption, 10-12 kg, and thats with a nice enginering feat.

A tuned to the max 50 cc moped engine-inside a reasonable limit and not using unobtanium piston and such can deliver 12-14 hp, but runs even over 25Krpm. Weight 7 kg, and no useable torque.

An engine specificly build for RW, a 140cc aircoled boxer with starter motor, was 7 kg, and ment to drive an hydraulic pump. but that one was never finished, because the crankshaft did prove a problem to make. (comparable engines can be found at the model shop, the largest engines used in model planes, and if you dont want chinese slave labor el cheapo stuff, youre looking at ‚+/-1500)

The larger, more powerfull model engines. forst of all ‚‚‚‚‚‚, and fragile for the application youre looking, but weight for power, you cant do better.

The old data I have from an Etec is that it does 11 Hp at max.But that means, on 36V you need batteries that can supply 305 amp for more than a flash. Meaning, youre looking at or very heavy SLAs of a good brand (Hawker Genesis pure lead technology or simular, like the Odyssee, Datasafe or SBS, all Hawker brand.) Or a serious amount of batteries like 3000mAh high grade NiMH or NiCD batteries. Another, equaly expensive solution is to have at least 8 10 cell A123 packs parallel.

Leo has a very valid point in the venue- comustion engine rules. Most venues are things like leasure centers, and those are not lenient towards fuel driven appliances indoors.