Well, I've decided to have a go at this...

**joey_picus** · 4th May 2009, 15:46

Welcome to this strange world Nick, I'm building/planning/designing something over the summer as well so should be interesting to see what I can learn from seeing the efforts of someone with better engineering facilities than me

Axe recoil can be solved easily by having a counterweight on the other end of the shaft...it adds weight (obviously :P) but Iron Awe 2 used that very successfully and had a very powerful axe as a result, running off full bottle pressure CO2 with no real recoil (although they tended to spend more time flipping people than axing them, heh)

I remember reading Thz had a custom made rod and the stock seals in the ram do the job nicely, might be worth looking at their site and see if there's anything on there.

**typhoon_driver** · 4th May 2009, 16:03

If you want to talk spinners add me on msn - xzibit206@hotmail.com

I've been playing around with spinning bits of metal since I was 14 and know a lot of the ins and outs of effective spinners.

Easy to build, difficult to master:wink:

**Metal Demons** · 4th May 2009, 16:34

Yep, just found the details on Terrorhurtz's ram seals... I would have thought that rack piston would have been absolute death to pneumatic seals but there you go, it works! Nice, lightweight, simple mechanism... though I'd put a guide roller underneath the rod on the other end of the mechanism to give things a little more support, as it wouldn't weigh much more.

I think it's going to be an axe... hell, maybe I'll build two of the damn things someday, or go for a modular setup... I can see a spinner being great fun, but barely being able to use it seems to be the problem.

What I envisage is CO2 bottle --> bottle valve --> Regulator --> master arm solenoid valve --> buffer tank with safety burst disk and system depressurisation valve (open to the air) --> high flow firing solenoid valve --> Single action ram with spring return (to save gas giving me more axe hits, and if the return isn't gas-actuated then I wouldn't need to worry so much about the cylinder end seals being compromised by the rack toothed rod) --> another solenoid coming off the bottom of the ram, to vent it once fired and allow the spring to return it. Safety-wise, that would allow a startup as follows:

Radio removable link in --> system dead
Motors/weapon removable link in --> system dead, verify solenoid valves closed (they would have indicator LEDs across them).
CO2 bottle ON, Regulator ON --> System live up to arming solenoid
Close depressurisation valve --> System post-arming solenoid now gas tight and ready to receive pressure.
Remotely via radio:
Master arm ON --> System fully live, buffer tank fills with CO2. Axe now ready to fire.

To close it down:
Turn off master arm solenoid remotely - no further flow from bottle/regulator.
Open cylinder vent remotely and hold open while firing the axe (axe return button)
Fire the axe remotely, everything in the system downstream of the master arm solenoid will then flow out of the vent solenoid. Empties lines and the buffer tank.
Take the links out.
Close the CO2 regulator and bottle.
Open the system depressurisation valve to ensure system can no longer hold pressure.

Just thinking this through... obviously a pneumatic axe would make a mess of anyone foolish enough to be in the way when it went off, so this seems to be the most sensible way I can think of to do it while minimising the risks of it taking my head off while working on the robot... If anyone sees anything really stupid I've overlooked, please do point it out!

I just added both of you on MSN, by the way.

**Metal Demons** · 5th May 2009, 13:20

Well, I've decided to go for a very low profile machine with a horizontal overhead spinning bar... the thought of clashing metal and showers of sparks just got too tempting. A big rack and pinion pneumatic axe therefore remains a potential future project, perhaps for a second robot...but that's a long way off.

The design is a low UHMWPE box (at least the chassis) robot with the overhead bar spinner, and spring loaded anti-wedge skirts all round... influenced by Hazard and Final Destiny from Battlebots. Ideally the skirts and top will be Ti, but we'll have to see about that... power will come from two 12v drill motors to move the thing around, driven on two front wheels and with the back end supported by a pair of captive ball bearings in place of the wheels...keeping the box level and allowing me to chuck the back end about nicely. (I'll consider that further as it comes, if it comes in lighter than the plan I'll go for chain drive and AWD).

I'm planning to go with a Sabertooth ESC, along with the dx5i Spektrum radio and lithium ion cells (A123s) for power. Weapon drive is something I'll decide on when I get the bar... I'll take a look at beefing up the existing gearbox with the bar (ex-2500w angle grinder), and if that doesn't look too practical I might end up biting the bullet and spending the ridiculous outlay on one of the TW 'boxes as they're for all intents and purposes bulletproof, or so I've heard, and pretty much dead reliable even under the battering dealt out by big spinner-to-spinner smashes. For drive, the Magmotor route seems tempting after a chat with Gary due to the sheer amount of grunt the thing has... an expensive beast, though, so we'll consider that when it comes. Plus, talking about Magmotors is getting to sound awfully vapour-bot-ish, so I won't get onto that QUITE yet... the weight for one and its batteries should be left available, though.

I'm planning to go ahead and start piecing the drivetrain together and getting hold of the bar, checking everything works, and then doing the old cardboard layout routine to finalise the dimensions - before transferring it over to CAD and CNCing the chassis and structural components.

**joey_picus** · 5th May 2009, 13:35

Oi, nothing wrong with talking about 'vapour-bot-ish' things :P

UHMWPE should be good, Craig uses it on The Saint's wheels I believe and it's quite stiff at 10-15mm thick (it's what I'm planning on using anyway, so it should be...if it isn't I may have problems)

I take it you're planning on the skirts to prevent you from getting flipped then? Having a big bar whirling around the top and the gyroscopic forces thereof will help keep you down, but with the sheer amount of flippers around at the moment I wouldn't assume that you won't get flipped. It does sound very mean though, hope the design works out...and hope I never come up against it

**Metal Demons** · 5th May 2009, 15:13

Oh, I fully accept the risk of getting flipped and not being able to right myself... that's what you get only being able to run one way up and no self-righter, after all

The idea of the skirts is two fold: to minimise ground clearance and therefore avoid flipping, and to try and guide any really obscenely low rammers/lifters/whatevers upwards to get smacked by the big spinning bar. If I get lifted up there's a third defence which is the bar knocking into the ground and hopefully throwing me away and back down... but we'll see when it comes to that!

As of now, the preliminary design is approximately 3 and a half inches high, with the bar spinning ~4 inches off the ground - which should send it smacking into most things out there I've heard about.

**tom_kane** · 5th May 2009, 16:51

I havenâ‚¬â„¢t read the rest of this thread so Iâ‚¬â„¢m not sure if anyone has said this, but can I just advise you, before you start collecting parts and start the build. Come to a show and see what kind of opposition you will have, how things have changed since RW and what we do etc.

I have seen quite a few people build feathers and then go to their first event with them. After the event, they will scrap the whole robot and start again. This is ok but...expensive.

Goodluck!

**psycho_fling** · 5th May 2009, 16:52

personally id make the bar spin lower becuase there are many low machines out there

**Metal Demons** · 5th May 2009, 19:00

Oh, I'll try to make it up to see what's going on when I can, hopefully sooner rather than later...

As for the height issue, with the bar on top I really can't see how to get it spinning much lower than 4 inches from the ground... maybe 3.5 or just over with both the top and bottom chassis plates in Ti, and that's pushing it. The disc motor and gearbox limits how thin I can make the machine. The idea of the sprung skirts is to force the lower machines up into the blade... I'll see how it goes talking to people. If it's too much of a problem I could always scrap the current plans and go for an undercutter...