Choosing lithium battery brand...

[Limitaneus]

Further to this thread (and continuing my tradition of Bad Robot Ideas), could I ask how easy it is to rewire something designed to run on mains electricity to run on LiPo batteries? My present design involves mounting a 1600W demolition hammer on the robot and setting up a power supply for it (it's designed for 230V, which means 7A current is required). What kind of batteries - and how many of them - should I be looking at getting?

[joey_picus]

I'm going to go beyond the battery question and suggest that this would be a bad idea - it would be against the rules which set a maximum voltage lower than that which is required.

[Limitaneus]

An entirely reasonable point. Might have to import one from the States, then, since they're on 110V over there. =]

In my defence, however, demolition hammers have been used on combat robots before - the RW Wiki informs me that a hardy beast called Roter Osche competed with one powered by an 8.5HP petrol engine back in the days of the Second Wars. Admittedly, it was a superheavyweight that weighed in at ~167kg, but that can probably be put down to '90s-era materials and build styles. =]

[Shakey]

The other problem is that that is most likely using an AC motor which either won't run or if you're lucky may be a universal motor that can run on DC but would see reduced power and have a lot of inefficiency to start with.

[Limitaneus]

Could you not just whack an inverter on it? Or would that just increase the weight to a ludicrous degree?

[overkill]

An inverter large enough to power a 1600W demo hammer weighs around 5.6Kg and is quite bulky (going on a 2Kw model for a safety margin). It would be far better to fit a brushed or brushless DC motor onto the hammer mechanism.

[maddox10]

Why bother? RC brushless motors come up to 10 kw packages in affordable* form.


Not the first roboteer that makes his own batterypowered tool from a 240V mains machine
(it's very easy to fit a 50mm outrunner in the body of a cheap anglegrinder), working that route should be a lot cheaper and inside the rules.

*affordable is a fluid term, different for everybody.

The cheapest way I see is to replace the AC motor with a series wound startermotor from a junkyard.

[Limitaneus]

All excellent points. Thank you very much! I admit that my electrical engineering knowledge could be written on the back of a postage stamp in quite big letters, but my fiancée's old flatmate Tim apparently builds and flies multi-rotor helicopters (I intend for both to be team members, assuming they're willing, of course). He can handle that - I have a pronounced spasm in my right arm, which I fear will not mix well with soldering irons, TIG welders, or precision cutting equipment. =]

Thanks again for helping me out. My overall plan is to follow maddox's advice and disembowel the demo hammer accordingly, then shock mount it as well as I possibly can, The central idea behind the weapon is to couple active damage from the hammer strikes (the 230V hammer I've been looking at strikes at 2000bpm) with the sheer amount of strikes through the metal chassis of the target spreading vibrations through the bodywork and knocking stuff loose inside. Hopefully it won't also deafen everyone in the building, but who can say? =]

[Yatcatcher]

Perhaps look at air hammers as an alternative? Possibly from a DC compressor or even from low pressure CO2? Not sure how practical it is but cheaper and maybe lighter.... https://www.amazon.co.uk/Silverline-...rds=air+hammer weighs 735 grams....

[Limitaneus]

That's an interesting idea, Yat. Given how light they are, I'm almost envisioning a bank of them on a kind of jaw-like setup, clamping onto the opponent from the top or sides (I've often wondered why more vert crushers didn't use additional horizontal clamps to properly corral their victims) and hammering away on them until something comes loose inside. I'd kinda love to see that sort of thing on Battlebots, actually - let's break Deadblow's record for most hits in a match! =]