inertia arrow rest

geoffretired

Supporter
Supporter
I started making an inertia drop away rest. The workings became so fiddly that I changed it to a drop away driven by the cable slider. In my research I contacted different rest manufacturers in US. I had noticed two different takes on the time of the drop. One side said their arrow rest stayed in contact with the arrow until the last mm or two before the fletchings passed.
Others, obviously, were dropping as soon as possible. I found this difficult to accept unless there is a case for both situations to exist and be successful.
The long contact was explained as, " guiding the arrow for longer, like a rifle barrel guides a bullet longer than a short barrel pistol"
The quick drop take was not explained (no reply to my enquiries)
I can guess that the quick drop theory is saying something like; less time on the rest means less chance of disturbing the arrow once it has started, and it is bending etc so give it some freedom.
I imagine the rest could drop too soon; before the arrow has sufficient speed to direct itself without support.
There is a similar difference with the springy lauchers. Some set them as weak as they can get away with, others are quite stiff in comparison. Is this really part of the same thing?
I am still curious as to the correct method for launching arrows from the rest.
Is there a scientific or mathematical ideal that can be satisfied by more than one solution?:boggled:
 

Rik

Supporter
Supporter
Springy launchers:
The principle is the same as with a flip rest, you want as little pressure as consistently holds the arrow up. In an ideal situation, there shouldn't be any late contact with the rest, but if there is, you want it to move as easily as possible.

Drop away rests:
There will come a point where the arrow doesn't need support. You see that in high speed video of a release. I don't know how you determine what that point is, though I'd guess there is a rule of thumb that may be applied. The "guiding the arrow" explanation is specious IMO. If your arrows need that much interference, there's something wrong with your setup. I think the "leave it to the last minute" approach is probably just over-cautious.
It occurs to me: if you leave the drop very late, how quickly does the rest fall? Does it just end up behaving just like a springy rest in that case?
 
R

rgsphoto

Guest
A bit of high speed video would be great here Geoff. As I see it the arrow floats in mid air quite soon after launch. A bit of + nock hight gives the arrow chance to clear the rest. It seems most compound archers favour a rest with just enough tension to hold the arrow up at full draw. I set mine to sag when the arrow is half way down the draw. I'm not keen on drop away rests as it's just something else to break down just when you don't want em to.
 

geoffretired

Supporter
Supporter
Thanks Rik and Rich,
Both of your inputs have cleared things up in my mind. I feel unhappy about guiding the arrow too far, especially as it is not flying in a straight line.
It would be very like the normal springy rest, except the fletchings would clear.
For those who set the nocking point high, there would be no advantage either as they have good clearance by design.
I appreciate the idea that simple is best as there is less to break. My interest in making things just takes over and I have to run with the addiction. I have shot hundreds of arrows from mine and found out the weaknesses. Those have been strengthened. All the moving parts are stronger than necessary, I hope:rottentom
What attracts me to the idea is that I can get close to ideal launch angle without having to worry about the fletchings catching. I built in an adjustment so the time of drop can be changed. Give it too much delay and all hell breaks loose when viewed with a paper test.
My latest, is to make a hydraulic resistance for the trigger of my release aid.
It will, when finished, allow continuous squeeze but will stiffen if punched.
It may give me some security while going through the rehab.
Thanks again for the help.
 
R

rgsphoto

Guest
geoffretired said:
My latest, is to make a hydraulic resistance for the trigger of my release aid.
It will, when finished, allow continuous squeeze but will stiffen if punched.
It may give me some security while going through the rehab.
Thanks again for the help.
Hmmm a bit like the fluid/solid properties of "cornflower"? Food for though, pardon the pun.
 
R

rgsphoto

Guest
geoffretired said:
Does cornflower have fluid/solid properties?:boggled:
Go down to Morrisons/Tesco, buy some. Mix it with water. In the bowl it will be liquid stir it slowly and it will remain fluid, stir it faster and it will stiffen up. Punch it and you will hurt your hand. Strange stuff Cornflower.
 
R

rgsphoto

Guest
geoffretired said:
Could I use it in my hydraulic damper?
I have no idea? Your the inventor Geoff, get experimenting. Honestly try it, it's really odd the way it stiffens up with agitation/violence. It is worth looking into.
 
R

rgsphoto

Guest
geoffretired said:
I've made the equivalent of a mini sized shock absorber. I'll fill it up and see what happens.
Thanks
Success may depend on the viscosity of the cornflower mix, you will need to play with the proportion of cornflower/water mix for optimum results.

There is a synthetic version of cornflower Geoff...watch this space
 
Last edited:

simon m

New member
Ironman
Have a look at motorcycle steering dampers.....used to stop "head shake" under large throttle opening......they prevent fast movement but turning the steering at normal speeds is possible.

Also some of the newer armour(in leathers) has a silicone layer in it that hardens when hit fast but is pliable when deformed slowly.

Just some thoughts.
 
R

rgsphoto

Guest
simon m said:
Have a look at motorcycle steering dampers.....used to stop "head shake" under large throttle opening......they prevent fast movement but turning the steering at normal speeds is possible.

Also some of the newer armour(in leathers) has a silicone layer in it that hardens when hit fast but is pliable when deformed slowly.

Just some thoughts.
Hmm bikes, what road bike do you ride Simon?
 

Max

New member
Geoff - cornstarch is the stuff you are thinking of - a non-Newtonian Fluid (not liquid). Actually a colloidal suspension - the individual particles in the suspension will slide slowly past each other but resist rapid displacement. This only happens when the fluid has a certain concentration of starch to water. It is great to demonstrate the principles of non-Newtonian fluids but not very stable. I would stick to basic fluidics or hydraulics, using variable restrictions. The SCAT release uses a similar principle, but backwards, so a timed release happens after the trigger is released as opposed to applying pressure to the release and waiting. Good luck!
 

simon m

New member
Ironman
History or currentely?.

VFR400
zx6r J1
zx6r A1p (trackbike)
Currentely
Fazer '05



Me and the fiance ride that(she got a license a year after I did)
 
R

rgsphoto

Guest
simon m said:
History or currentely?.

VFR400
zx6r J1
zx6r A1p (trackbike)
Currentely
Fazer '05



Me and the fiance ride that(she got a license a year after I did)
I miss my bike ....sob
 

Adam

Active member
rgsphoto said:
I have no idea? Your the inventor Geoff, get experimenting. Honestly try it, it's really odd the way it stiffens up with agitation/violence. It is worth looking into.
Same as custard powder, and it's called a thixotropic substance if my memory of school science is correct.

Geoff, I presume your "inertia" rest will be similar in priciple (if not in practise) to the old Barner rest?

Adam
 

Rik

Supporter
Supporter
And of course there was a practical demonstration of the effect, on Braniac - Jon Tickle walking across a swimming pool full of custard.

It was fine until they got him to stand stil and demonstrate how he would sink slowly, with no vigorous movement. The problem was lifting him out again...
 

geoffretired

Supporter
Supporter
Thanks for all the helpful info. i am curious about cornstarch but water and aluminium together worries me. The restrictors are the bits I'm on at present. Not much room for error in the sizes so I will be some time getting it right.
Adam remembers the Barner rest??!! I made one like it but it was too bulky. I then replaced the piston movement with a pendulum. The weight on the end gave the inertia. However I could not get rid of variables as the machining was needing to be accurate beyond my means. So now, the cam is held in its cocked position by a post that can be pulled away by a system of levers and cams that are operated by the movement of the cable slider. I can e-mail pics but not sure I can post them here. It is very simple and works consistently. Thanks again for all the advice
Geoff
 
Top