How bad of an idea is this?

Hello! I've been cooking up a design recently and I'd like some input from people who even slightly know what they're talking about, since I, er, don't. At all. Oh well.

Basic plan is to ape Barber-Ous but go a bit bigger. How much bigger? Well, my plan was to nab a stainless steel beer keg and use that for the drum section instead, along with some dirty great teeth made out of, I dunno, probably Hardox. Everyone uses Hardox now. It's like coke was back in the Thatcher years; not something you wanted per se, but almost necessary to live through the madness of the age.

Sorry, I get sidetracked easily. A 50-litre EuroKeg of the kind I intend to use (for reasons other than the fact that I can get them for cheap, I assure you) weighs, according to this 'ere distributor, 11.8kg, so I've planned for the actual drum itself (with the addition of all the teeth and so on) to come to a max of 20kg. I reckon I could bump that up by welding panels onto it, but I don't know whether I'd even want to. Anyway, the plan is to get that spinning as fast as possible around a central axle, have two sturdy wheels at the side, and put any allowed weight into getting the drum moving even faster. What I want to know is this: will it suck as an idea, rip itself apart due to the forces involved, or actually sort of work? A bit? Ish?

I have to be honest, this is my first attempt at a competitive robot design. Please don't go easy on me. Tell me what I need to know so that I can learn from this and improve. =]

The wall of such a keg is waaaaaay to thin to withstand even an attack from a decent featherweight spinner.

As Mario says, the material is simply too thin. One hit from near enough any machine would dent it.

Righto. I thought that might be an issue. I did want to make a big, tall drumbot, but it might be worth just having the spinning section be, like, just a Hardox or wear plate octagon with some teeth on it that spins around. I'm getting the image of something rather... agricultural, and to be honest I'm completely fine with that.

Whilst on the theme of people who don't know what they are doing....

I am looking at mobility scooters as a source of running gear for a bot. Any suggestions? Are they too weak? Too slow or what?

I would have a go!

The comments are right it would be too weak.
But it would be different and you could enter as a pub team!

I think the thing could work on TV, but I don't think you would necessarily get too far.
First thing find out as much as you can on how they got Barbarous to work then go from there.
good luck

Mobility scooters aren't of much use unless you go for a huge wheel like chimera. It's been years since they have been the go to motor.

Or the NPC64's. In theory also mobility scooter motors, but for heavyweight US citizens.

Most wheelchair and mobility scoter motors over here are rather weak, with the 250-350W @24V rating.

The old "series 6-7 standard " was a 750W rated motor, the now no longer available Bosch 750 GPA. Just to give an idea of what's "normal".

A super easy and powerful, albeit a slightly more expensive option is to use these: http://ampflow.com/wheelmotors.htm

The F30-400-G with the 6 inch wheel is probably the most suitable for combat. Very much a plug and play solution; doesn't need any modifications to use.

So 750W is the general level people are using... OK.

Where do you get the motors that are in use now and how much do they cost?

That's 750w continuous rating. Most motors quote peak rating which are quite a lot higher but may be less powerful.

The motors. If you want "budgetfriendlier" motors, you're looking at the 1000W Chinese scootermotors from ebay and simular.

otherwise, Iskra has several usable, but heavier motors. Finding those , any decent hydraulics firm can help there.

Other option is to get in touch with the Italian brand Movimotors. Brutus went from LEM130's to those, and it wasn't a bad transition.

Finaly, Ampflow. Expensive after importing them, but easy to find and order.

http://pp3d.co.uk/getting-started

Quote:

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Originally Posted by typhoon_driver

http://pp3d.co.uk/getting-started

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Thanks. That has taken a while to absorb.

Next question; What is a good hydraulic piston and where do you get a suitable one?

A good one is one that will contain the pressure you plan to run it at and has a bore large enough to give you the force you want (you will need to run the numbers) with the stroke that you need for your weapon design.

In terms of locating one I'm assuming we are going second hand? In which case, ebay, gumtree, local scrap yards, farm auctions, dealers in farm machinery etc would be your best bet. You could go for a custom solution but of course expense comes with that unless you can machine it up yourself.

http://www.ebay.co.uk/sch/i.html?_fr...inder&_sacat=0

Quote:

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Originally Posted by Mouldy

http://www.ebay.co.uk/sch/i.html?_fr...inder&_sacat=0

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Thanks but...

Let's assume I am going with this;

http://www.ebay.co.uk/itm/Hydraulic-...Sh7-lt9AzHIgpg

With a 25mm rod size and a 250mm stroke and a bore of 40mm.

How much force do I get out of it? What pump and stuff do I need? Errrr???? Help......

http://bfy.tw/8CZ4

Google is your friend.

Those rams are rated @210 bar continous and 250bar intermittend.

Affordable gearpumps in smaller sizes can go up to 250 bar. But in the somewhat larger size, it's 210 bar.

By coincidence, the old maximum pressure on hydraulic pressure.

So, 2/2*3.14*210= 2640 kg of force.

@250 bar = 3150 kg.

For comparisation, Razer was around 6500 kg.

Thanks,

Why is the area 2/2 Pi not 4cm² Pi?

And will the compression force be the same or less (I would expect it to be less).

And what do you do for electric power to the epump does it come with such???

Thanks to all the experienced roboteers who've been replying in this thread! You've all been amazing and just so helpful. I really appreciate you taking the time to answer newbie questions.

So. I've refined the "enormo-drum" bot idea a bit, and have elected to go with eight 6mm Hardox/similar plates welded to the outside of the now-notorious 50L Eurokeg. Powering it has proven to be an issue... until I stumbled upon this 'ere site concerning performance dirt bike engines. Of note to me was the performance listed for the second entry (I don't recall whether or not a liquid-cooled engine would be legal under Robot Wars's rules wrt chemicals, so I'm not going to chance it), at 9HP at 11k RPM for only 7.5kg in weight, plus the puncture-proof tank and enough fuel for a 5-minute fight - I say five because, well, it wouldn't do to underestimate how much fuel the thing needs and run out of puff in the middle of a battle. Not good telly. =]

Between the output of my 9HP air-cooled dirt bike motor and (I did the maths and added a bit more on to account for the teeth) a 45kg spinning drum, we might get a pretty reasonable drum spinner out of it. What are the thoughts of veteran (to say nothing of sane) roboteers on this solution?

Area of a circle is radius x radius x3.14

It's just coincidence that 4 cm diameter the same result gives for the diameter and 2 times radius.


Basic formula for hydraulic power and motor needed. Pressure x Flow/500= Kw needed.

Thanks. It's been a long while since I did maths....