[HELP] How to amplify a linear motion?

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ANTALIFE

New Member
Hey RPF I come for help, but first off here is a video of the assembly I am trying to make

I am working on a firing pin assembly for a cosplay rifle (AR2 from Half-Life 2) and have found a bit of a problem with my design. In the game the firing pin moves horizontally like this:

Currently I am using a solenoid to drive the firing pin directly, but this only gives me a stroke length of 40mm (at the limit of using a solenoid). The problem is that I need the stroke length to be at least double that (80-100mm). So, the question is, would yous know of a good way to mechanically amplify the linear motion? So far, I am thinking of using a rack & pinion combination like this
Also, I have thought of using linear motors or servos but the issue is that they won't give me the speed or thump I am after
 

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JPH

Sr Member
This may not be the answer you are looking for, but 40mm movement will be plenty cool. You want gears strong enough to handle the motion and light enough to not require a heavy system to move those gears. You have to figure out how/where to place the gear system and its power.
 

lmgill

Sr Member
As you double stroke, you will double load, so as long as you mechanism is light an the return spring is not to strong, you could use a bell crank. A linkage arm with a the pivot point half the distance to the solenoid side than the "firering pin" side, will double your stroke.
 

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TazMan2000

Master Member
How about a set-up like a steam locomotive drive? The larger the wheel, the longer the stroke.

TazMan2000

Let me correct myself, as a steam locomotive works the opposite way. You want to convert rotational motion to linear motion.

The video will show you. Just have a cylinder that the piston or firing pin can slide back and forth through. The motor being used is geared down. You will need to look for a DC gear motor that reciprocates at about 100rpm revolutions per minute or in your case, rounds per minute.


TazMan2000
 
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ANTALIFE

New Member
This may not be the answer you are looking for, but 40mm movement will be plenty cool. You want gears strong enough to handle the motion and light enough to not require a heavy system to move those gears. You have to figure out how/where to place the gear system and its power.
Yea, if I don't work something out I will just use the 40mm stroke distance as is

As you double stroke, you will double load, so as long as you mechanism is light an the return spring is not to strong, you could use a bell crank. A linkage arm with a the pivot point half the distance to the solenoid side than the "firering pin" side, will double your stroke.
Oh yea, have not heard of bell cranks before. Thanks for the suggestion

Let me correct myself, as a steam locomotive works the opposite way. You want to convert rotational motion to linear motion.

The video will show you. Just have a cylinder that the piston or firing pin can slide back and forth through. The motor being used is geared down. You will need to look for a DC gear motor that reciprocates at about 100rpm revolutions per minute or in your case, rounds per minute.


TazMan2000
Hmm, don't think I will have enough room for that sort of setup, thanks for the suggestion though
 

propmaster2000

Sr Member
Do you also want it to be as rapid as shown in the video reference?
Also, it is a bit trickier to replicate something in real time (real life), as well as doing it in the small space required (shown in the animation).
 
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ANTALIFE

New Member
Do you also want it to be as rapid as shown in the video reference?
Also, it is a bit trickier to replicate something in real time (real life), as well as doing it in the small space required (shown in the animation).
Yup, plan to have it as rapid as in the video, hence why I went with solenoid initially
And yea do understand the limitations, but see it as an engineering challenge ;^]
 

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TazMan2000

Master Member
This is about as small as you're going to get unless you find a long stroke solenoid that moves as fast as you want it.

Mechanism.jpg


TazMan2000
 

McFlyte

Active Member
If you're going to add gears anyway I'd skip the solenoid and use a motor to drive the gears. You may need some limit switches to control the motion, perhaps motor timing would be sufficient. I'm also not sure how noisy it'd be.

I'd try TazMan2000's idea first.

This is about as small as you're going to get unless you find a long stroke solenoid that moves as fast as you want it.

1581471625493.png

To add some detail; the bar that's rotating to transfer motion may need to be slotted, or use some arrangement to ensure the rotational motion doesn't bind up the mechanism. Also, to double the throw, the distance between the pin joint and the top bar needs to be double the distance between the pin and the solenoid.

Keep in mind that doubling the throw also halves the force transferred.

If you're feeling game perhaps you could modify the solenoid to increase the throw or build your own?
 

TazMan2000

Master Member
If you're going to add gears anyway I'd skip the solenoid and use a motor to drive the gears. You may need some limit switches to control the motion, perhaps motor timing would be sufficient. I'm also not sure how noisy it'd be.

I'd try TazMan2000's idea first.



View attachment 1256376
To add some detail; the bar that's rotating to transfer motion may need to be slotted, or use some arrangement to ensure the rotational motion doesn't bind up the mechanism. Also, to double the throw, the distance between the pin joint and the top bar needs to be double the distance between the pin and the solenoid.

Keep in mind that doubling the throw also halves the force transferred.

If you're feeling game perhaps you could modify the solenoid to increase the throw or build your own?


A much better explanation and diagram.

TazMan2000
 

kermet

Sr Member
I'm not to sure about this thinking about it in my mind and this may be wrong and really a quick thought but what about a magnet on each end might work just a thought
 

Senden

New Member
Since its purely cosmetic, what about attaching the bolt to to solinoid with a long, weak coil spring, kind of like a double action switchblade.

(picture courtesy of wikipedia)
px-Automatic_knife_out_the_front_double_action.svg.png



When this solenoid triggers, the spring will compress, before accerating the bolt forward to its maximum extent (with a nice meaty smack if there's a strike face installed) before accelerating backwards with the retracting solenoid (if correctly timed) back into its enclosure.

There would be some bounce but if its fully retracted that won't be visible (or can be damped with a little friction near the end travel).

And you have the advantage of a mechanism that is less likely to damage (and be damaged) by curious fingers.
 

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propmaster2000

Sr Member
Question:
What do you figure the "actual" range of motion of the firing pin is itself, while firing?
.
If it is only a small amount of distance, then your solenoid is all you'd need to function "during the firing sequence".
But, when it is to be reloaded, the pin needs to move back a bit more to clear the space and then reset.
.
Maybe you can design it to have the solenoid/shaft mounting bracket slide back as one unit to open the gap, then return to the
forward firing position after it is reloaded....
 

Duncanator

Sr Member
Hey RPF I come for help, but first off here is a video of the assembly I am trying to make

I am working on a firing pin assembly for a cosplay rifle (AR2 from Half-Life 2) and have found a bit of a problem with my design. In the game the firing pin moves horizontally like this:

Currently I am using a solenoid to drive the firing pin directly, but this only gives me a stroke length of 40mm (at the limit of using a solenoid). The problem is that I need the stroke length to be at least double that (80-100mm). So, the question is, would yous know of a good way to mechanically amplify the linear motion? So far, I am thinking of using a rack & pinion combination like this
Also, I have thought of using linear motors or servos but the issue is that they won't give me the speed or thump I am after

Your double rack and pinion idea should work, but you'll need them to be well supported or you'll be stripping gears pretty quickly.

Concerns:

-You'll also need to make sure your solenoid is strong enough to move the second load, as the force from the secondary rack will have half the power of the solenoid rack. Also you'll lose some more power to friction.

-The firing pin assembly will want to be sturdy, but as light as possible, so it will have minimal inertia for the mechanism to overcome. It's being asked to do a lot of rapid directional changes (as I'm sure you are aware.)

-The "thump" that you want should come from the weight of the solenoid slug going back and forth, not the firing pin. This will put less strain on the mechanism. We experimented with this type of haptic feedback on some VR guns with some success - the heavier the solenoid slug, the more "thump."
 

propmaster2000

Sr Member
Since a solenoid uses an electromagnet, that has already been used and may still be used in the final design.
The issue is the length of travel of the shaft (80mm to 100mm) needed, not the motion required to get the
distance. You would also need a spring to return the shaft back to it's original position so the solenoid (electromagnet)
can pull on it again in a horizontal direction and not rely on gravity to make it work.
 
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