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Total Recoil - Chunkulator - NSW
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chunkulator



Joined: 27 Jul 2016
Posts: 219


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Total Recoil - Chunkulator - NSW

I am planning to build a spring-powered flipper for Vivid. Working name at this stage: Total Recoil. I was thinking of Captain Hooke but too subtle I think.

Anyway, I successfully prototyped my spring tensioning mechanism today:


Here's a video of it in action:
https://www.youtube.com/watch?v=-f76DW9hJe8

Those are two of the biggest extension springs you can buy at Bunnings. It's built around a length of 40x40x2.5 SHS with a 16x35x11 bearing in each end. A length of M16 threaded rod runs down the centre with a nut on it with a couple of pieces of 12mm rod welded to it. The rods stick out the tracks and engage with the springs. The threaded rod is driven by an ATV starter motor ($25 on Ebay from a local supplier) through a #25 chain and sprocket drive.

The plan is to pull the springs back and get them to hold on a catch. Then, driving the nut all the way forward will release the catch and deploy the flipper. Next to build a shorter version of this rig and attach it to a flipper to see what it does to a 13.6kg weight.

Post Sat Feb 18, 2017 7:36 pm 
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Nick
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Joined: 16 Jun 2004
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Location: Sydney, NSW


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Its about time we had another spring powered bot on the scene! Smile. That video looks good; the speed pulling back the springs is faster than expected and the motor is up to the workload.

The real challenge is getting the springs to latch, release and then re-engage with the bolt and pins. If you are up for different ideas, I have a mechanism that bypasses many of the problems and even doubles the firing rate. I can sketch out a quick diagram if you are interested.
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Post Sat Feb 18, 2017 8:46 pm 
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chunkulator



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I think I have a mechanism that will work. I'll post some pictures once I've got the CAD finalised. I wasn't planning to use a pin and hole mechanism but a spring-loaded rotating cam that engages with a bearing for easy release.

Post Sat Feb 18, 2017 9:06 pm 
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pilleya



Joined: 31 Mar 2016
Posts: 91
Location: Sydney


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It seems like a Choo-Choo mechanism could be quite effective in pulling back the springs, with an electromagnet which hold the spring in place once fully retracted, a electromagnet will most likely give you the smallest delay possible between pressing fire and the opponent being tossed into the air.

Post Sat Feb 18, 2017 11:40 pm 
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chunkulator



Joined: 27 Jul 2016
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Oo! Electromagnet's an interesting idea, although I guess it would need to be a seriously beastly one. Something like they use to hold doors open in hospital corridors maybe? Or maybe I should shut up and start winding?

Post Sun Feb 19, 2017 6:52 am 
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chunkulator



Joined: 27 Jul 2016
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Here's where I got to so far:


Cut away showing tensioning mechanism:


Cut away showing latch mechanism:


This is sitting on about 13.4kg right now excluding fasteners, wiring and ESCs, so I need to find a way to shed some weight.

Post Thu Feb 23, 2017 9:47 pm 
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chunkulator



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I was playing around with the prototype tensioner a bit more over the weekend trying to work out what gearing I could get away with. It stopped working mid-stroke, so I tore it down and discovered that my M16 mild steel threaded rod was being completely stripped by the load of those springs.

So a bit of a rethink is in order. I have a piece of actual 16mm trapezoidal leadscrew and a brass leadnut leftover from my CNC machine build. However the leadnut won't fit down the centre of the SHS and I can't weld to it. A different way of holding the leadscrew and mounting the leadnut will be needed.

Post Mon Feb 27, 2017 7:26 am 
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Nick
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Well, That sucks! You lead screw will have lower friction than the original thread & nut but you might also look at salvaging the screw and nut from a car jack, You can pick one up cheaply from a car wrecker and if you get one from a small hatchback, the parts will be smaller and might fit.
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Post Mon Feb 27, 2017 7:42 am 
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Valen
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would just going to a high tensile threaded bar and nut be enough perhaps?
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Post Mon Feb 27, 2017 7:55 am 
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Nick
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With a couple of said nuts to distribute the load?
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Post Mon Feb 27, 2017 8:02 am 
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chunkulator



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Good suggestions, thanks! I'm going to try to make the real leadscrew work first. It's kind of the correct tool for the job, after all (ball screws aside). I already have a prototype mounting rig with a rail. I suspect I might need more gearing though. The leadscrew is 4mm pitch whereas the M16 rod is around 2mm.

Anyone have any comments about the workability of the latch mechanism I've drawn?

Post Mon Feb 27, 2017 8:05 am 
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Nick
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Its a bit hard to say how well it will work from the drawing. One thing I remember from watching countless fails on the Junkyard wars show - release mechanisms under high tension have a huge amount of friction, so releasing the latch might take more force than you expected.
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Post Mon Feb 27, 2017 8:51 am 
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chunkulator



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True. I have designed it so it has a few things going for it in the ease-of-release department:
1. The pin that the catch engages with is a ball bearing, so the catch can roll off it easily.
2. The catch itself runs on a ball bearing.
3. The catch moves exactly at right angles to the force it contains.
4. The mechanism that drives the catch is the same leadscrew that did the tensioning, so it should be strong enough.

Let's hope all that is enough!

Post Mon Feb 27, 2017 9:58 am 
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Valen
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I suggest making that bit easy to replace, if(when) it wears or breaks it'll be in the middle of an event
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Post Mon Feb 27, 2017 2:58 pm 
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chunkulator



Joined: 27 Jul 2016
Posts: 219


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My old friends at my favorite Ebay store "CNC and Cupcake World" (who also do a side line in beer brewing gear) sold me a trapezoidal lead nut that I can weld to:

http://www.ebay.com.au/itm/16-x-4-HEXAGONAL-TRAPEZOIDAL-NUT-ACME-SCREW-LEAD-CNC-ROUTER-MOTION-MACHINE-DRIVE-/302088908086?hash=item4655e6ed36:g:VFIAAOSwAuZX2JD2

I'm hoping that's problem solved.

Post Mon Feb 27, 2017 8:38 pm 
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