Shooting machine

[DC]

This is just a little look at my shooting machine. I found early on that I wasn't very consistent shooting through the chrono so I built this to eliminate the weak point---me. It's very consistent, within 1 or 2 fps every time. It's really just a crossbow with a chrono and an automatic release. The trigger mechanism is a rolling block. The trigger itself is the silver finger on the bottom of the sliding mechanism. It contacts the pin which goes in the hole for the draw length you want. The DL release can be fine tuned by the height of the pin. I'm very pleased with the trigger mech but I have some reservations about the saddle that the bow sits in. I found it hard to make a saddle that would hold the bow securely but also fit different handles. If you can come up with a really slick saddle I'd love to hear about it. Hopefully you can see everything you need in the pictures but if there are any questions, fire away. Pictures are in no particular order, sorry.

[DC]

More. The pulley on the trigger mech is just to make it easier to pull.

[DC]

More

[willie]

cool contraption Don, pretty simple but effective trigger. Do you have to have the bow clamped in very hard to get consistency with the speed?

[DC]

I haven't noticed that the pressure makes much difference in the results but I always do it the same so there wouldn't have been any difference, I put the bow in and squeeze the jaws shut with one hand and then spin the knob in with the other. The jaws are lined with wet suit foam. I do have to re-adjust the bow sometimes. It moves sideways a touch so that it isn't aimed through the sweet spot of the chono. I wonder if that movement changes the results but I haven't noticed any more than a 1 fps difference. The thing that amazes me is how consistent it is. If something does go wrong it's because I didn't aim the thing right. The usual "gone wrong" thing it a 55-60 fps result so it's not  possible to think that it's a real result. I haven't figured out what causes that. It must be triggering on the fletching or something.

[Tuomo]

Nice shooting machine!

Please, could you add a few photos of the machine with the bow and arrow?

[DC]

Here ya go. I modified the saddle after Willie's suggestion.
Sorry, no full draw

[Del the cat]

Nice... wish I had more room ! 
Del

[DC]

With a little crowding you can get the thing in 15" including room to operate. Take a couple off that if you only use one chrono. It would have given more room to have the bow vertical but I don't use a shelf. Not a big problem as Markus(I think) said. I do like the windows of the chrono  looking at 90° to the bow. I think it makes it easier to properly trigger the chrono. Hard to explain in twenty words or less

[JEB]

And why do you use that?

[DC]

My thing is speed. I'm not a good archer(poor hand eye coordination) and I was getting very inconsistent results shooting through the chrono manually. I built the machine to get the consistency I need to know if a modification was an improvement.

[DC]

Question about the automatic trigger. You can see the trigger in Reply No 1, third picture, it's the tin covered thing sticking out back. It rides up on the peg that is in the desired DL hole shown in Reply No2 second picture. That pulls the trigger.

[DC]

I modified the saddle. I turned the whole assembly around so that the back of the bow is against the fixed jaw. This makes the draw length independent of the handle thickness. I'm a little leery of having all the force against the movable jaw but it is substantial. I'm thinking of ways to make it just a little safer.