Let's Make Robots!

Laser Tag and Recoil


It's me and my laser tag project again. This time you'll read about me trying to find a solution to simulate the recoil of real weapons to make laser tag more realistic and cool to play.

First part of the page will be, as usual, the brainstorming part. That means that i really do not know what i'm gonna use for the recoil mecahnism (and if i will be using one, if it gets too complicated or costly i'll just abandon this idea) so i ask you for suggestions.

 What does it have to do to properly simulate recoil?:

- it has to be a fast mechanism considering i might get up to 15 virtual bullets per second (it might also work once every to bullets, bringing the count down to 7 "loops" per second at most)

- it is preferrable if the mechanism works with electricity and not gas or air

- it has to be a bit powerful, not too much but at least it has to give you the "blowback" feeling

 What i have considered so far: 

not much actually. I have read that solenoids might do the job, but i don't know whether they are fast enough and where to buy them. I also checked out linear actuators but they seem to be costly and slow. Dual shock-like motors (the ones you find in xbox/ps/wii controllers) are the easiest and cheapest solution, but i'd keep this as a last resort, in case i can't come up with anything else, because they don't give you a "kick", they just make the gun vibrate (not very realistic). 


I am concentrating especially on solenoids. They look interesting, but i really do not know where i can get fast and powerful ones. My idea is to attach a weight to the solenoid arm and switch it on and off everytime the user presses the trigger.

Any suggestion/idea? 


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I like the approach you show in your diagram above.

Consider that the force delivered when the spring pulls the blue weight down needs to be enough to be felt by the person holding the gun.  The stronger the spring is, the stronger force it will apply.  Then you'll also need a motor and gear that supply enough torque to overcome the pull of the spring.

You also have other practical considerations, like the amount of room you have to fit the device in the butt of the gun. You might start with that as a limitations and build something like what you have above. Then you can experiment with different springs, motors, gearing, etc.

Cool idea. Good luck.

Do you think a wooden structure would be ok? ...Because that's one of the few materials for which i have the tools for cutting it. I don't think i know where i can find springs though, i'll need to find myself an internet supplier.

As for the torque needed, is there a way i can know how much torque i need before i buy motors or is it just a matter of experimenting?

Last thing, i don't think i'll be using the setup i've shown above, because i haven't got much vertical space. I think i'll go for the horizontal setup posted before. 

I find tamiya prepunched flat metal plates great for making up sturdy structures that might be difficult to do if you don`t have a machine shop in your other pants. I get them 4 for $1.50. It`s not the cheapest way to go but you can make a prototype with it, and once it`s working change to aluminium window frame stock to make the rest.

If you went the motor and cam route, you would need a motor that can do 900 rps to get 15 bullets per second. What if you internally modified the firing code so that a minimum "shot" contains 3 bullets? So if you could click the trigger for the minimum time, 3 virtual bullets are fired off and the recoil system is run, then when you go full auto you get 15 rounds per sec, 3 bullets in each shot, 5 pulses per sec for the recoil system. It might be easier and cleaner than 7. Your motor rpm would have to be at least 300 which is more reasonable than 900.

With the spring.. the longer the travel on your ram the weaker your spring can be but the bigger the cam has to be to get that travel. I`m sure a mathematician could come up with the calculations relating ram travel and spring strength with the kickback force gained but I would just experiment.

No springs? Try rubber bands for now.

I think i'll go for the wooden prototype first. Then i could see how much it would cost to get the same parts machined, with metal instead of wood. Thoguh i think it's gonna cost pretty much, like 100$ or so... 

Out of curiosity i also want to try a coil design, i know it eats a lot of current, but still it's design would be much simpler, and i could manage to build every part by myself. (coil design simply means: have the same spring-weight system, but instead of having a cam pull it back, use a coil) E.g.: i could fit everything in a pvc tube and that's it. Not to mention it's smaller.

...Even if i agree that the cam mecahnism, without considering costs, is the better one. 

About the three bullets per shot: i also thought about something like that when i said 7 bullets instead of 15, i'll just drive the cam once per 2 bullets or 3 or more, definetly more reasonable. 

Necessity is the mother of invention, they say. Try it with wood, or stock metal angle parts if you can get them.

There are spings in lots of things, try to scrounge some up. My local hardware store stocks a variety, but you may not be so lucky.

You could look up the equations to calculate the required torque, but basically you need a motor and gear set up that is powerful enough to overcome the pull of the spring and any weight attached to it.  Given the limited space you will have to work with, I'm betting you will have not too many choices of motors. So perhaps a good approach would be to get the most powerful geared motor that will fit, and work backwards from there.

Limitations can be a good thing. The remove variables from the design. Then you just have to select and design around them.

Airsoft guns have a mechanism that works like this:


It cocks the air pressurer (is that how you say it?) which is the grey bar at the top and once it has reached the end it is released back by the spring (as you can see the black gear has some teeth missing which allow the bar to be pushed to the left by the spring).

It would be hard, but i could reverse the motor's polarity and change the springs position (left instead of right). But these motor are quite powerful, so they also draw much current from the battery. Not to consider that sometimes they fail, but that could also happen to the solenoid mechanism. 

Another thing to consider: each airsoft weapons comes with its own motor and its own gears, this means that different weapons could lead to different recoil power (=bad). 


I could actually try your (TeleFox) setup, but i need to search for a powerful motor first (would this also draw much current? Just asking...). One last thing: how much current does a solenoid draw? 

I tried to draw what it was that I was trying to say and if faild. 

And yeah, solenoids draw lots and lots of current.  

Solenoids draw a lot of current.

Alternatively you could use a spring loaded ram similar to a solenoid but use a motor to cock it. Have it so that when the motor turns it draws back the ram and when it reaches its limit the spring slams it back against the butt of the gun.

It probably couldn`t manage 7 rps though.

You mean something like this?:

I was thinking along the same line until I read your post =D
Should provide a decent sound/movement provided the parts are well chosen, and I don't think it would be too hard to get the repeat rate above 7 shots per second. If you add a contact or shock sensor to the metal stopping plate then you could have the recoil imitator feed back into the controller, ie: to ensure you get the correct number of recoils for the number of 'bullets' fired.

Yes very similar except for the motor actuator. I was thinking of a disc that starts small but gradually gets much bigger. My sketchup drawing of the disc is really wonky but you should get the idea.

The rotating disc pushes the ram back slowly until the pin comes back to the start of the disc.