Spring Loaded mechanism Design Help

[EddieV]

I'm narrowing down my search for a CNC machine to a few options now, but i have a question about designing a spring loaded mechanism.

I'm building a small scale robot which will operate under remote control. (pics on a thread later when i get building ) Because channels on the transmitter are limited, im trying to build a mechanism which will crank back and then shoot out, using just one single direction servo and a spring.

I guess the most similar in principle would be like the part on a stapler which pops forward, or maybe think drawing back a crossbow string.
I think having the assembly driven by a toothed cog on a rail to pull it back. When it reaches a certain point, the strut is released and the spring drives the assembly forwards quickly. Then it can be drawn back again.

Hopefully that makes some sense, i will do a sketch of what i had in mind, when i am back with my graphics tablet.

Does anyone have any suggestions or experience with a mechanism like this? Im completely new to designing functional pieces, so this is a bit of a first foray!

Cheers
Eddie

 

[blighty]

quick look on the net

https://home.howstuffworks.com/nail-gun.htm
[ame]https://www.youtube.com/watch?v=fCdKIVtSbTM[/ame]

are you trying to shoot something like a BB, or an arrow type thing?

 

[BillH]

I'm narrowing down my search for a CNC machine to a few options now, but i have a question about designing a spring loaded mechanism.

I'm building a small scale robot which will operate under remote control. (pics on a thread later when i get building ) Because channels on the transmitter are limited, im trying to build a mechanism which will crank back and then shoot out, using just one single direction servo and a spring.

I guess the most similar in principle would be like the part on a stapler which pops forward, or maybe think drawing back a crossbow string.
I think having the assembly driven by a toothed cog on a rail to pull it back. When it reaches a certain point, the strut is released and the spring drives the assembly forwards quickly. Then it can be drawn back again.

Hopefully that makes some sense, i will do a sketch of what i had in mind, when i am back with my graphics tablet.

Does anyone have any suggestions or experience with a mechanism like this? Im completely new to designing functional pieces, so this is a bit of a first foray!

Cheers
Eddie

Channels are limited? My Taranis QX7 is a $110 radio that has 16 channels and with a $40 module plugged in the back will do 32 channels.

 

[EddieV]

Thanks blighty, that's good inspiration. I just have to sort it so instead of a lever handle, it has a rotary input from a servo.
Essentially shooting an arrow 2cm out then retracting it again. Rinse and repeat.
I'll sort some sketches and images today

Bill, yea they can have lots of channels with the right receiver. But the lightweight receiver i am using has 4 channels. It weighs 4g

 

[Blogwitch]

If you had a rack on the spring loaded 'piston' bit, you could drive it with a small cog coupled to your servo.

To get it to automatic fire at the end of a back stroke, just cut two or three teeth off the drive gear.

So the sliding component would be wound back to it's start position and when it hit the taken off teeth area of the drive gear, it would automatically release itself forwards under spring pressure and once past the missing teeth, the drive gear would re-engage and wind the piston back to the start position until it hit the missing teeth section again and so would repeat until you stopped the input gear from turning.

I hope that explains things easily enough

John

 

[EddieV]

If you had a rack on the spring loaded 'piston' bit, you could drive it with a small cog coupled to your servo.

To get it to automatic fire at the end of a back stroke, just cut two or three teeth off the drive gear.

So the sliding component would be wound back to it's start position and when it hit the taken off teeth area of the drive gear, it would automatically release itself forwards under spring pressure and once past the missing teeth, the drive gear would re-engage and wind the piston back to the start position until it hit the missing teeth section again and so would repeat until you stopped the input gear from turning.

I hope that explains things easily enough

John

Ahh that's genius! Thanks for the description. I had the vision of the rack and gear to drive it back, but never would have though of cutting out some of the teeth!
Time to mock this up in CAD this evening

 

[Wizard69]

I work in automation, especially packaging machines, you would be surprised what you can accomplish with chain and cams. Search around for articles on chain guns (cannon), high speed packaging machinery, cam design, Scottish yokes, old shaper drive mechanisms and so forth.

Given that a better description of what you want to do would help.

 

[Blogwitch]

I used to work in machine areas that were all mechanically based, even envelope making machines that were over 60ft long, with not one part that wasn't mechanically driven. OK we had microswitches and magnetic sensors on them but they just ran the counting system (40K pieces per hour) and of course the electrical drive system.
It was amazing to see some of the mechanical solutions they came up with to change direction of the drive train and still be able to handle very fragile reels of paper.

If you want to pursue the mechanical direction and get loads of ideas to solve mechanical problems, then there is a book I often refer to. I downloaded it off the net but can't remember where from, it is called -

Five Hundred and Seven Mechanical Movements - H. Brown (1871).pdf

And was printed in 1871, but like everything else, almost everything we do is governed by old techniques.

Just search for exactly what I have printed above and you should be able to download for nothing.

If you want to pay for it, then just search out the modern reprint of - "507 Mechanical Movements" and pay your money to Amazon etc.

Another good one is - The Engineer's Sketchbook Of Mechanical Movements 1902.pdf

Which actually shows over 2,600 different drawings of all sorts.

Well worth searching out.

John

 

[TonyM]

Why not use a simple cam. or just use a solenoid.

 

[EddieV]

Wizard: Thanks! That proved to be an interesting lunch-hour google!
I roughed out a quick animation (in 5 minutes, it's very buggy, apologies!)

http://g.recordit.co/OGCNabUvGm.gif

I think that is what i am aiming at for now. I just need to make sure the servo which will turn the cog can be precisely controlled so a complete cycle of "wind back and fire" can be done with a button press

Blogwitch: That's great - i just picked up a second hand copy of 507 mechanical movements from ebay. Should prove to be a good introduction to making functional things
(Hats off to H. Brown for breaking from the conventional "501" books. Good to know he pushed himself that bit harder to detail the last 6! haha)

Tony: Im not sure a cam would do the job? (or i cant envisage how to implement one for this :S)