[MOC] LEGO Technic Working Crossbow

[Naturalbornuser]

It is exactly a reversible compound crossbow because the system is inverted compared to the "normal" system - here the string is further from the holder,
and thats why the equipment gains more compact dimensions and a longer run for the bolt. It looks like:

 

And with the system stretched:

I didn't cover the construction except for the handle and left the look raw in a typical technic style to focus mainly on efficient operation and during shooting so that there was no effect of bricks falling off every now and then. The crossbow has a trigger mechanism with an automatic fuse - it works so that you need to press the red FIRE / SAFE button to press the trigger. After the shot, when we put the string back on the "hook", the fuse pops back into the extended SAFE position. Below is a few-second video showing the most important thing, i.e. how it shoots:

If anyone is curious what the range of shots is, they will find the answer at the end of the main video :)

 

I will say right away that it is not very impressive, but for a model made of bricks, I think it can be - a substitute for shooting rather than spitting out arrows :) More photos as usual at my FLICKR and on Polish forum: LUGPOL Regards to the forum :)

Edited April 4, 2023 by Naturalbornuser

[Naturalbornuser]

I have problem to add photo to display in post instead of link. How to do it?

[SOLVED]

Edited April 4, 2023 by Naturalbornuser

[Davidz90]

Very impressive! I like Your earlier compound bow as well, very clean construction.

Surprisingly poweful for the springs used. I wonder how much more these limbs could handle. Reinforcing them with arched panel pieces is a nice idea.

A few years ago I built a reverse draw crossbow as well, reached 50 m/s velocity. You can see it here:

https://www.youtube.com/watch?v=zRED3K14D84&ab_channel=DavidZiemkiewicz  

I used shorter, faster limbs (reducing limb inertia is crucial) and way bigger springs. Worked nicely for few years, but eventually the limbs gave up and broke.

[Naturalbornuser]

50m/s is very great result. Actually I have chronograph and I can check speed of my arrows. Of course I will write the result :)

Springs you used are impressive :) Are you Lugpol member?

Edited April 3, 2023 by Naturalbornuser

[Davidz90]

12 minutes ago, Naturalbornuser said:

Are you Lugpol member?

No, only active here and on Youtube. 

I considered buying a chronograph, but in the end measuring bolt drop and high-speed videos like here:

https://www.youtube.com/watch?v=LamPgTpAIro&ab_channel=DavidZiemkiewicz

provided accurate enough results. If I remeber correctly, springs were from garage doors; they had approximately 20 kg of pull each and it shows on slo-mo video - the crossbow really tries to shake itself apart :P

There are few very nice design features of your crossbow, like the large pulleys; I used very small ones for strength, but at the cost of increased friction. 

[Naturalbornuser]

I know, but general look and similarity to the original was for me important while constructing it :)

[Mr Jos]

Hope you had safety glasses on with that misser, that thing flew damn fast around!

Nice builds you've made!

[2GodBDGlory]

Impressive and cool-looking! Good work!

[Milan]

Frontpaged.

[Naturalbornuser]

Thanks very much :)

Edited April 7, 2023 by Naturalbornuser

[Naturalbornuser]

As I promised I made measurements  speed of various arrows using chronometer. The results you can see on short video below:

 

 

Edited April 12, 2023 by Naturalbornuser

[Davidz90]

Amazing! 19.8 m/s is a very respectable number given the relatively small springs. 

[LEGO Train 12 Volts]

Simply amazing! 

[Jim]

This would have been a clear winner in a "Non-vehicle contest". Awesome job.