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#1
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Re: pic: Another Belt-In-Tube Drivetrain
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Belt / pulley strength is a function of two things - the diameter (tooth count) of the pulley, and the width of the belt. A larger diameter pulley decreases the force put on the belt teeth a given output torque. A wider belt decreases the stress placed on the tooth by spreading the force out to a wider area. As belt sizes get thinner and as pulleys get smaller, eventually you start to skip teeth via ratcheting, and eventually you'll fail a belt. In a drivetrain, with HTD belts, 24T pulleys and 9mm wide belts are riding on the edge of feasibility - these drives tend to fail belts by ratcheting and eventually tensile failure. I haven't experimentally determined how small of a pulley you can go to in order to safely use a 15mm wide belt - I'm sure I could estimate it with some math, I just haven't done it. I seem to recall 18T pulleys would cause 15mm belts to skip in a drivetrain, but I don't remember if that was speculation I heard someone else say or something actually based on real world experience. |
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#2
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Re: pic: Another Belt-In-Tube Drivetrain
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#3
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Re: pic: Another Belt-In-Tube Drivetrain
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Most likely, if we stick with belts, is to go with GT3/GT2 like 971. |
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#4
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Re: pic: Another Belt-In-Tube Drivetrain
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Edit: Google says 2x as strong. |
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#5
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Re: pic: Another Belt-In-Tube Drivetrain
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The difference between trapezoidal and HTD is just as great somehow. It's a shame that GT2/GT3 is patented, otherwise Vex would be able to produce them (I think?). Does anybody know why Vex doesn't use GT2? Also, can GT2/GT3 belts be used with HTD pulleys, and what effect does that have? |
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#6
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Re: pic: Another Belt-In-Tube Drivetrain
Do you mind providing details on what parts you were using and how it failed? The 18t VexPro timing pulleys are plenty strong enough for use in an FRC drivetrain under normal conditions, but as Chris explained earlier, there must have been some slippage and racheting going on that lead to your failure.
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And yes, I believe that GT (3mm) belts can be used with HTD (3mm) pulleys, and if I recall correctly, it performs about as well as HTD with HTD. |
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#7
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Re: pic: Another Belt-In-Tube Drivetrain
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971 helped us out and pointed out that these belts are being loaded beyond their recommended limits. We built a calculator just to double check belt loading. We also swapped a bunch of belts on the same drive rail and noticed despite the same CC, the tensions were different. We try to reduce belt load and build in tensioners which is what we did this year. The last conversation I had with the students is that we are in the mood of having the drive on the practice bot survive with minimal maintenance for over 1000 simulated matches. we are just sick of worry about this stuff, so keep in mind that perspective. I think using 22 tooth pulley and 15mm wide GT profile belt will be a step in the right direction for Ty's design, which is pretty sweet. |
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#8
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Re: pic: Another Belt-In-Tube Drivetrain
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#9
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Re: pic: Another Belt-In-Tube Drivetrain
That's excellent, thank you! Any chance you can also throw in testing of HTD so that teams can compare your data against something most teams are more familiar with?
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#10
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Re: pic: Another Belt-In-Tube Drivetrain
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As a side note the pulleys we sell and future pulleys we will be releasing are the actual GT profile. The pulleys are free game for anyone to sell/make just not the belts sadly. Thanks! |
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#11
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Re: pic: Another Belt-In-Tube Drivetrain
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