1. damn that sounds like such a pain to deal with lmao i'm glad i gave up on rollers
i highly doubt it's the shaft's specs causing the issue, there are some bleutec 145cm 4-bands with 7.5 and 8mm shafts so a lot more load on the shaft and they seem to shoot ok. crazy recoil aside
2x soft 14,5mm bands is like a 70kg load it's practically nothing
have you checked the offset on all parts? handle, barrel, muzzle. lower offset on the barrel or/and higher on the muzzle can cause shaft bending
2. i just checked out its effects on underwater projectiles. i did give it a second run and it says that
- As the spear accelerates, cavitation bubbles form along its surface, especially near the tip and any protruding features (like barbs or notches). These bubbles collapse violently as the spear moves into higher-pressure zones, creating shockwaves and localized turbulence.
- This collapse (called cavitation erosion) increases hydrodynamic drag compared to a perfectly streamlined, non-cavitating spear. The spear slows down faster, reducing effective range and impact velocity.
as for what we can do about it i don't know. high velocity is almost always guaranteed with any two-band classic setup, rollers and invert rollers will have maybe slightly lower maximum velocity ceiling. but if we try to bring the speed down then the speargun is simply not powerful enough, so we basically just have to deal with it. considering the super powerful setups that exist out there (3x16 with 6,75 comes into memory) and shoot incredibly well, i don't know if it's a significant issue. probably not. it definitely doesn't seem to play a role in performance by itself
3. that could be something to measure, definitely. what info would it give us that would allow us to tune setups though? i'm confused as to its application
4. yes that's what i called "coasting"
wouldn't it be easy to pinpoint it by the spear's velocity rate though? as soon as it starts decelerating it has exited the equilibrium state
my guess is this would correlate with KE and overall performance. so we can use our current understanding as a proxy for it in terms of what bands to use. because deceleration is involved, inefficient equilibrium duration would mean a worse shot and efficient = good shot. or would that be an inaccurate guess?
Appendix:
i'm pretty sure we can test that with invert rollers. get a 1x20+1x14,5 setup and compare to a 2x20 setup
or for a classic just set a tripod and measure performance. e.g. does it reach 4m at max 150ms?
as for not mixing together rubbers for invert rollers, i will have to take a hard stance on that that it's mistaken. we have real life experience of thousands of such setups performing better than other setups with similar rubber diameters. ultimately what matters is just the force an individual rubber pair can exert, and the stored energy in it, resulting in total work done over the barrel.
basically every observation we have is that it works well. so the right approach according to the scientific theory is to assume that the mix (eg upgrading a 3x16 to 1x19+2x16) is the logical way to improve shot power and not the other way around as it is unsupported by any observation
we can speculate as to the why, but we already know that it works fine. for classic setups i'm not that sure, from experience mixing rubbers can work fine too with no visible drawback, the power is just inbetween, kind of like 1.5 is between 1 and 2.
so in theory there could be some losses, or some discrepancy... but when used, it's not enough to make a significant difference.
i did use ai again for it. gave it the inputs of 25m/s for band A and 28m/s for band B
"
Why "maximum speed potential" is misleading
A rubber band doesn't have a fixed "max speed" it can give any shaft. That speed depends on:
- Shaft mass (same here)
- Barrel length (same here)
- Force profile over distance
If band B alone reaches 28 m/s, that means the integral of its force over the barrel length (divided by mass) gives that velocity. Band A alone gives 25 m/s. When both pull together, the total force at every point is FA(x)+FB(x)FA(x)+FB(x). The total impulse is larger than either alone, so kinetic energy is larger → speed > max(25,28).
Simple example with constant forces (to illustrate)
Assume:
- Shaft mass m=1 kgm=1 kg
- Barrel length L=1 mL=1 m
- Band A alone: constant force FA=312.5 NFA=312.5 N → work = 312.5 J312.5 J → v=2×312.5=25 m/sv=2×312.5=25 m/s
- Band B alone: constant force FB=392 NFB=392 N → work = 392 J392 J → v=784=28 m/sv=784=28 m/s
Together: Ftotal=704.5 NFtotal=704.5 N → work = 704.5 J704.5 J → v=1409≈37.5 m/sv=1409≈37.5 m/s
That's higher than both.
In reality, forces aren't constant, but the principle holds:
the sum of two positive force curves yields a higher integral than either individually.
"
Not sure if the final output is accurate (highest number i've seen measured is 42m/s). there is a speed cap on shafts from what i've seen where it's super hard to gain any additional speed (but increasing mass can lead to higher energy).
EDIT:
I also asked it to clarify because at this point i haven't delved in this theoretical areas before
"
"Mechanically linked" isn't a fancy physics law name—it just means
connected so they must move together. In your setup, both rubber bands are attached to the same shaft. The shaft is a single rigid object. When it moves,
both bands are forced to change length at exactly the same rate because their rear ends are fixed at the muzzle and their front ends are both tied to the same moving point (the shaft).
The underlying physics principle: Kinematic constraint
In mechanics, when two objects are attached to the same rigid body, their motions are
constrained. The relevant law is that
the velocity of the attachment point is the same for both bands.
Mathematically:
Let L1(t)L1(t) = length of band 1, L2(t)L2(t) = length of band 2.
The shaft's position x(t)x(t) relative to the muzzle determines both lengths:
L1(t)=x(t)+constant1L1(t)=x(t)+constant1 (if attached at different notches, the constants differ, but the rate of change is the same).
Thus:
dL1dt=dL2dt=dxdt=vshaftdtdL1=dtdL2=dtdx=vshaft
So both bands
must shorten at exactly the shaft's speed. There is no way for one band to shorten faster than the other because they are tied to the same moving object. That's the constraint.
Is this a law? Yes, it's from rigid body kinematics
It's not a separate "law of mechanical linkage" but a consequence of
Newtonian mechanics and the definition of a rigid body. If two points are fixed to the same rigid body (the shaft), they have identical velocity. The bands' attachment points are on the shaft, so their velocities relative to the muzzle are identical.
So to directly answer: Yes, it's a real physics constraint
It follows from
Newton's laws and the fact that two objects attached to the same rigid body must share the same velocity. There's no separate law named "mechanical linkage", but the concept is fundamental to how constraints work in mechanics.
"
so, good to know i guess LOL. had no idea
here i would ask a question that oldheads tend to ask: is all this necessary? for me it looks way too theoretical, since we can already tell what works even if we don't really know the why. so for example if someone advises to not do X, but we can do X and see that it's more powerful than Y, the advice is just erroneous (falsified) no matter the reason (or how much counter-intuitive it was). like something i've heard from an older spearo, "if the shaft acceleartes more slowly while in the barrel then it has more time to be charged with energy". but this never worked in practice (and now we know it's because of work done, not "time under tension" which doesn't make sense here)
Bonus:
"Because real bands have no low speed limit, they both pull throughout – no capping. The shaft speed is determined by the
sum of forces, not by a slow band's limit.
That's why speargun you can add multiple bands – more force, more speed, no downside except recoil and aiming difficulty."
