180 degree pneumatic hammer mechanism?

Hi,

I'm looking for some help with a 180 degree pneumatic hammer design
Would you say this is the best/usual method to achieve what I am planning:
Attachment 10018
This just uses a crank to convert the linear motion to rotational. I've read in a few posts and on other sources that a rack an pinion system can be used with pneumatic linear actuators to create hammers/axes, but I can't visualise how the pneumatic ram connects to the rack to push/pull it.

I am considering a hammer for my middleweight design, Creep, ideally being able to invert and strike in front and behind the robot (think of a pick axe head). The bot design thread is here: https://www.fightingrobots.co.uk/thr...266#post477266

Any help would be greatly appreciated!
Dan

The rack and pinion system is the best here. Thor uses this method to great effect. I would have the ram directly attached to a toothed bar that meshes with a MOD 3 upwards gear.

Im currently designing a feather pneumatic axe which uses a modified top of a ram and toothed round bar for the piston.

Using the crank style, you will never be able to go full 180 as the ram piston will want to pull horrizontally to itself and will jam the arm as it cant force the rotate. It will work as long as you dont make it go full 180. It will put itself under alot of stress as it nears the '0' and say '270' degree mark, and will also - IIRC, it will loose speed as it approaches the max and min points of its rotation.

rack and pinion are the way to go for full power along the whole of the stroke.

Quote:

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Originally Posted by Ocracoke

I would have the ram directly attached to a toothed bar that meshes with a MOD 3 upwards gear.

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I've been wondering about something like this, but I'm struggling to visualise how the rack will be secured. It seems like it will need some sort of linear slide/rail.

Quote:

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Originally Posted by Roboteernat

Im currently designing a feather pneumatic axe which uses a modified top of a ram and toothed round bar for the piston.

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This sounds very cool. I read another post from Maddox about customising the ram by replacing it with a round bar rack and pinion, but I'm not sure how you're supposed to get a pneumatic seal with all those grooves cut out! Unless it doesn't fully retract but is a longer shaft that leaves all of the toothed section outside of the cylinder...

Custom pneumatic rams seem like a fairly specialist and expensive option though. I imagine you'd have to get this certified again for pressure too :?

Quote:

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Originally Posted by Roboteernat

Using the crank style, you will never be able to go full 180 as the ram piston will want to pull horrizontally to itself and will jam the arm as it cant force the rotate. It will work as long as you dont make it go full 180. It will put itself under alot of stress as it nears the '0' and say '270' degree mark, and will also - IIRC, it will loose speed as it approaches the max and min points of its rotation.

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Yeah I knew it didn't look the most efficient or practical for a back and forth rotation.

just quick reply, The way you seal the end is to custom make an end cap thats longer so that it is longer than the pitch distance of 2 teeth. that way you get a seal between teeth. usually a ptfe block is used as the seal
A very quick reply explaining that, when im free i can add drawings.

I can add a few links that should be useful to visualise the pneumatics.

The first are some renders from beta in Battlebots, arguably the most powerful pneumatic hammer out there.

https://i.imgur.com/aMMf8El.jpg

https://i.imgur.com/V0rq21j.jpg

For a smaller version of this style of mech, here are so photos from No Toy/Little Hitter, a pneumatic featherweight.

https://i.imgur.com/6xKONky.jpg

https://i.imgur.com/XO2MqaT.jpg

https://i.imgur.com/X5PCvvI.jpg

This is awesome info Shooty! I hadn't thought of a vertical pneumatic ram and it makes perfect sense. Very cool.
But it doesn't look like Beta has a double acting cylinder so how does the hammer retract?, I can't see the weight of the piston being enough for gravity to pull it back.

Thanks Roboteer, that's good info about the PTFE end cap. Are these modified commercial pneumatic rams, or are the builders just machining the cylinders and pistons etc, and having them certified?

Beta has a double acting ram, so there's a second small valve at the top that can fire to bring the hammer back down (running at 140 psi). The Beta FB page has a few more details on it, but those are the basics.

Its a mix of custom ram for some builds or modified rams. You will find higher end bots such as beta will have custom made rams.
For those with lower budgets, its easier to modify an existing ram. I have some festo rams and im just swapping the top cap and shaft on mine, but i have also machined ram parts for feather builds - i do custom cnc machining for quite a few roboteers.
One example is the feather diotior, that had a custom ram setup. You can see the PTFE? block in the images above, its that cream thing on top of the piston. It may be nylon? not sure till i sort my test one out!

Shooty is correct, there is a 2nd ram which operates at a lower pressure to fire the ram down. it means less f a good hit in the reverse, but less air is used to retract meaning you have more for that big blow.