Yes. 10char
Belts donât âstretchâ in any amount that isnât negligible.
BUT there is a side of tension and a side of no tension when under load.
There is also the width of the belt. While the width wonât determine a different stretch, it will determine how resistant the belt is to bending. The velocity of the belt can cause the belt to push inward/outward from centrifugal and centripetal forces depending on the point in time at axis of rotation(around the pulleys).
To counter act this inward/outward motion(secondary function) automobiles use idlers, idlers primary function is belt tension, its secondary function is reducing belt slap from changing RPMs.
Wider belts slap less and keep their trajectory around a closed loop with less deviation.
What your feeling as âmore torqueâ from a wider belt, is less deviation of belt trajectory. Yâall might think the belts go from point a to point b in a straight line, but they donât, there is oscillation.
When you have two belts with the same tensile strength/mm of width, the wider belt with more mass being driven at the same velocity as narrower belt, will have more kinetic energy and hold a more of a true path with less oscillation (belt slap).
A belt that slaps more travels farther with less energy transfer. A belt that slaps less will waste less energy in oscillation and transfer more power to the second engagement point.
The other piece of wider belts is it allows more surface friction, more friction is harder to make the belt skip.
/end topic
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People are speaking in relative terms here. If you assume all the conversation is in absolute terms then you end up needing an endless volume of words to describe anything and end up sounding like youâre writing code for a computer.
If my wife asks me to hand her the set of keys touching the magazine on the table, and my reply is, well the keys are not touching the magazine because according to particle physics nothing is actually touching anything, itâs all an illusion due to repellant forces at a quantum level, sheâs going to look at me like Iâm crazy. If you say belts do stretch but the context is do they stretch in a way that affects their use in esk8, youâre kind of missing the question in context which is that they donât stretch in an appreciable way to this application. In a specialized and technical context youâre right but thats not the context of this conversation.
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It actually started with a hypothetical, then some kid tried being smart saying belts never under any circumstance stretch in any way. So PXSS did what he should have done, looked up the terms related to it. It was also mentioned in my original comment that the stretch that happens but almost non-existent.
Some kid? Are you retarded? Seriously, Youâre not right. You can chip away at reality little by little with physics arguments just so in some miniscule way, for some reason that doesnât apply to our builds or the entire automotive industry, you feel right. Can you personally pick up a belt and stretch it like a rubber band? No.
This isnât about my hatred for Hubs. Iâm fine with hubs. This is about you guys trying to prove a point that you canât. Timing belts donât stretch.
You think they do so prove it by showing us actual stretching. (Not bending, or crimping, or wearing teeth) Stretching.
Oh! And call me a kid to my face.
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I donât use molecules in my belts. So there.
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When you say âyouâreâ, you mean everyone except for @racidon and @PXSS right?
Because they have stretchy belts.
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Iâm putting a poll up to take tally so vote away.
- Belts do stretch
- Belts donât stretch
0 voters
Cool! Finally a reply that isnât just rude! I appreciate that. Let me tell you why I think your example and mine are different.
Yes, I agree that if we were talking in terms of molecular physics. This would be silly. Do you know how much belts stretch for our application under tension? I sure donât. Thatâs why in my initial comment I stated this:
So, we are in agreement that the stretch might be negligible. I never denied that, but if the manufacturer of the belts themselves say that elongation due to tensile forces needs to be taken into account in the design of a drive, Iâd be a terrible engineer to simply dismiss that. Would you not agree?
This is a quote from the design guide for drive systems from gates (manufacturer of htd5 belts that everyone uses).
Now to some math on our application. E: you can skip this next paragraph if you donât like math. The important stuff is on the next oneâŚ
At 36V, a hard acceleration from stand still can draw up to 40A from your battery, correct? That equals to 1440W. Lets say you lose 20% to efficiency, thats 1152W of power. Now we can assume that our rpm is low, lets say 200rpm. This means a torque of 55Nm at the motor shaft and 55Nm in the opposite direction at the wheel pulley. We know the radius of a motor pulley is roughly 5mm and the radius of the wheel pulley is roughly 30mm. That means 11000N of force in the motor side and 1833N of force in the opposite direction at the wheel. Now assuming that one end is fixed, the equivalent would be pulling one end with 12833N. What is the length of the belt were pulling? Center to center distance should be a close approximation. 65mm is close enough I think. So if we were to apply 1283kg hanging from a 65mm long belt, would it stretch? In standard units that would be 2881lbs hanging from the belt. That is without including any shock factor into the equation.
E: continue here if you skipped the math
2881lbs = 19 of me hanging from 65mm long x 12mm wide belt⌠Yes, thats an idiotic amount of force on a tiny belt. Will the stretch be at a molecular level? I donât think so. I think the stretch would definitely be measurable with standard tools. Will it be significant enough to affect the operation of the belt? I still somehow think it would be negligible but without me assuming a youngs modulus I cannot give you a quick and dirty estimate.
E: assuming the same Youngâs modulus as fiberglass and that the tensile member takes up the whole backing area of the belt⌠Elongation of a 65mm x 12mm width belt under tension from a hard acceleration is⌠0.8mm That is 1.25% elongation. Belts never stretch at all. Yeah right⌠If we assume the tensile member only takes 33% of said area, the elongation increases to 1.6mm or 2.5%
Again, I agree that if we were talking about stretch at a molecular level, this would be silly.
All of the threads here somehow always become toxic and more about calling the other guy an idiot. If you have a valid argument, there is a polite way of expressing it. I will entertain conversations with polite people like you seem to be. If the opposing argument is ânah, youâre wrong, why? Because I say so brah. Youâre stupidâ or a slightly wittier variant then Iâm not going to even try and debate because obviously we will get nowhere. This is the main reason I stopped posting 6-7months ago. People canât just have a civilized conversation here it seemsâŚ
Tldr: Elongation of a 65mm x 12mm width belt under tension from a hard acceleration is at least 0.8mm That is 1.25% elongation.
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I just went back up and read where this whole argument started. It was a hypothetical scenario where belts dont snap or skip⌠Way to take things out of context
A series of rude out of context replies by psychotiller is all it took for what seemed to be constructive conversation to become toxic. Way to go!
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It really comes down to the material properties of the tensile member, which is why there are some differing opinions here. Polyester-reinforced belts are more elastic and better at absorbing shock. Fiberglass-reinforced belts are stronger with less elongation. I doubt many of us are using kevlar/aramid beltsâŚ
If youâre not familiar with the term âModulusâ, it is the Modulus of Elasticity. Basically it is a measure of a materialâs stiffness. (Actually it is the slope of the stress-strain curve in the elastic region, but Iâm not going to get all enginerdy on you). In simple terms, pull on it this much and it deforms this much. High modulus = low stretch
- E_polyester = 2 Msi
- E_fiberglass = 10 Msi
From the same document:
SDP-SI says they donât stretch:
⌠and then goes on to say they stretch 
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2 walls of texts to say. âI have no experience using belts but maybe they stretch enough to matter, here is a rabbit hole of math and science.â
Then you have mechanics with experience saying, âThey donât stretch.â
Maybe if people talk more and listen less this conversation would start going somewhere.
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Sweet, I used 10.4427 MSI as the estimate
They donât stretch over time (because they are only loaded in the linear elastic region)
They do stretch under tension. Everything does.
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Slap a TLDR and we can end that argument.
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Dear God is it over?
Just go ride your fricking skateboards
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fuk that we need to determine whether hub motors stretch
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Only in real life, on paper they hold tight to the canâŚ
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