Want to know more about spring tension and spring compression in electric Airguns

[mike111]

Hello,

I expirement with my own diy electric gearbox for electric airguns, and i wonder if anybody could guide me to information on:

1) In an electric gearbox, is the spring pr-tentioned when not shooting, or is it completely loose, without tention at all?
2) What is normally the distance, in mm, the spring is compressed , from rest (pre tention rest or no tention) until it is compressed max just before fireing?

3) How much power (Nm or Kg) is necessary, to do the compression from rest (pre tention rest or no tention) until it is compressed max just before fireing?

I do know that this is all about the type of spring i am using, but lets say it is for a spring used in a pro-line hardball rifel with a nozzle speed of lets say 130 m/s, i just need some average numbers.

Thank you very much in advance.

 

[Prisce]

Best people to speak to would be @Sitting Duck and @Hangtight, they both know more about gearboxes than I know about breathing.

 

[mike111]

Thank you very much Prisce.

 

[SCAR_Jester]

It could be an idea to try and talk directly to manufacturers who design them?
American companies may be easier to talk to like Elite Force, Krytac.
Or perhaps Nuprol from Europe.
Or if you want to try translating through email, Tokyo Marui are the best of the best in design, they would surely know these numbers.

 

[Adolf Hamster]

if it helps, i did some proper instron testing for a project of mine that was very similar.

i was using a kind arms v2 box with the spring rated for 1j of mozzle energy

ended up you were talking about 20n preload and 66n at bottoming out over ~56mm of travel. and roughly 2.5j of spring energy to get 1j of bb energy.

iirc the stroke of the box by the gearing was something like 48mm

View attachment 34964

 

[Sitting Duck]

FUCK ME - I just try to ensure the bastid things operate correctly & efficiently

The spring is mildly compressed anyway....

a spring's "usual" & aprox length is about 160mm to say 170mm untensioned

(basically the length of the v2/v3 gearbox)

By the time it is inserted it is compressed to about 125mm aprox depending on certain factors

In operation the spring may be compressed down to as little as 50~55mm in full final compression at point of release

In general cycling of the gearbox and depending how fast it cycles, if it has Active Braking etc....

It is very likely some "over-spin" occurs as the piston releases but the energy of motor continues (now free of tension),

until it is slowed quickly by the tension of spring in drive chain, so it is common to see some pre cocking/tension

This spring's actual compression can vary LOADS in operation.....

the spring's original length 160~170mm aprox

then is compressed to fit inside box 120~130mm

BUT depending if bearings/spacer is used this can often be 10~15mm extra compression of spring in fitting

which then in normal operation can often over spin/cycle to compress spring to say 95~110mm and the above 10~15mm

So a spring which started at say 170mm, can be moderately pre-cocked on semi at say 100mm after firing a shot

before it is then retracted fully to say 55mm or a third of its original full length say

Depending on a full stroke where the piston is fully retracted and spring compressed

the piston/sector gear has usually 16 x 3mm teeth in a std geabox

but due to the teeth & where they mesh the stroke of the piston will be greater than expected 48mm

more like add a couple of teeth (18 x 3mm making a 54mm stroke compressing spring to release)

However more variables like using a shorter stroke ( removing some on of the sector gears 16 teeth )

to lower the energy produced by lowering the spring's final compression/tension

Not going to cover Short Stroking or even the half stroke Dual Sector Gear which fires twice per cycle on a half stroke

But final spring compression or tension can vary LOADS depending on each individual case

Even if you say a regular full stroke gearbox used there are factors like 10~15mm effecting the initial spring tension inside box

Then different springs, different metals, some springs fitted in reverse can add extra 10fps aprox

altering the pick up point or Angle Of Engagement will reduce stroke and I guessing slightly slightly increase the tension on spring

in its initial starting point when inserted inside by about 2mm - though we are concerned mainly by stroke & aprox 10~15fps loss

(NB I say initial tension btw, the final tension of spring remains unchanged on release of piston if correcting AoE)

Just because a spring is shorter/longer than another means jack

in short - pahhhhhhh since when was a post of mine brief......

the spring when fitted is say 125mm or 5 inches

which is then compressed to say 55mm or 2 inches

often in operation there might be some extra tension for over cycling a little

so the spring might be compressed to say 100mm or 4 inches as it slowed the drive chain to a stop

but depending on bearings/spacer used inside piston you might be compressing 12.5mm more (half inch)

But yeah ball park figures are 160 ~ 170mm original spring length

125mm fitted

to say 100mm operation (could be less as explained depending speed/spacings)

55mm aprox at final release at full retraction with mild piston spacer/bearing spring guide

The rest of the energy in Newtons or whatever - FUCTIFINO is the answer

I just worry how it all works

You get the thing operating smoothly & efficiently as possible

you see what power you need & adjust the spring or its power to level needed

other planning is how fast the gun will cycle and issues you might experience

together with volume for the barrel length being used, the bb's mass you are using

on top of the current or power required or the best way to plan for that build's specification

In general there are loads of headaches from these poxy toy guns already

but usually we stick with a good general basis of what works based upon tried & tested builds

Sod working out all the Newtons and stuff though - never looked into it THAT much

(I'm sad but jeez even I draw the line at overthinking or studying stuff in that much detail for my needs/ability)

 

[Hangtight]

There will be some preload on the installed spring, but it will vary. Basically a properly volumed set up will recover about 80% of the energy stored in the spring and convert it to kinetic energy in the BB.