Hey everyone! Here’s a pic of my rubber band ramp. I’ve tried multiple styles of ramp from foam and plates to lexan and I’ve found that the elastics haven’t failed me and have been the most consistent of the methods considering my available materials (I’ve been in my home workshop with only what I could take in a box from my org before and in-between shutdowns. There’s really consistent compression and I like the overall design and concept. Have any of you considered or used elastic feeder ramps for your rollers, and have you seen any additional benefits?
Expect a late season reveal in the upcoming weeks. Uploading: D0830034-D5F1-498F-858E-88B9D332B18E.jpeg…
I have tried this in the past, but the only thing that I don’t like about it is that it doesn’t do a great job of centering the ball in the robot. I use two pieces of c-channel running parallel to each other, covered in anti-slip. Works pretty well, just a thought.
Oops. Let me try that again.
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Looks good. I have no idea how you keep those columns from bending…
Loctite and a wish. The reds are #32s so they don’t put too much force on the standoffs.
Ok so rubber band ramps can be extremely efficient in the right scenarios. I can’t tell how well yours would work just from the picture but I can confirm that rubber band ramps are not horrible. I don’t think you need it that dense though because that lessens the elasticity a lot which is a major reason for the ramp. Also 580x the 1# bot in Texas and a team at my school have been using rubber bands as a ramp for a while. For some ramps sometimes they interfere with the goal you are shooting or intaking from… but with a rubber band ramp it can be further back in your bot. And since the rubber bands are flexible it technically gives you more space for you initial intake and vertical intake for your ball to pass through. This is just my thoughts on it from my experience so honestly just go with what you think here.
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Actually the exact opposite. Elastics have completely variable compression based on room temperature, humidity, how long the bands have been stretched for, etc etc etc.
The point being, rubber band ramps are very inefficient (comparatively speaking). Also, consider the mechanical energy wasted from the uptake rollers (technically the motor) in order to deform yet a second set of rubber bands (the first set being the one on the rollers).
There are even more factors to consider, but I’d argue the main advantage a rubber band ramp has over a rigid polycarbonate ramp (for example) is space efficiency but that isn’t an issue this year as there is ample space to make whatever subsystem work with a snail bot (generally speaking).
As for the benefits of a polycarbonate ramp (done correctly) well there are too many to name but a few of the obvious ones –– uniform compression, exact and rigid geometries, can easily increase coefficient of friction to increase efficency of the system (with mesh or adhesive foam), etc. The main downside to using polycarbonate is that it’s a lot harder to get it to work well and to get the maximum benefit of what I mentioned requires CAD skills and manufactoring skills (though not so much when you have a CNC).
Just my two cents –– don’t be so quick to dismiss other options
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This is a cool topic, and I’m glad you brought it up. For anyone curious, this also applies to rubber band rollers, flaps, compliance wheels; anything that undergoes viscoelastic deformation loses mechanical energy due to something called viscoelastic hysteresis (one of the primary factors of rolling resistance). While ‘compliance’, or ‘grip’, or ‘traction’ are good, they often come with the downside of increasing this viscoelastic resistance to motion. Some materials are inherently better at this balancing-act than others, like certain grades of rubber (not all rubber is created equal), while others are less so, like steel (steel has a very low rolling resistance as well as a high load-bearing capacity- making it one of the primary materials used as the wheels on a train but as a consequence of this low rolling resistance, steel has very poor ‘traction’, which is why sand is often shot in front of the wheels when the train has to accelerate).
But, given the limited material options available in vex, I’ve personally found it more effective to optimize the geometry of a system rather than the material. So while the materials you use to transmit energy to the game elements is important, it doesn’t tell the full story.
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I always feel like my brain expands a little when reading your posts. Like, I would’ve known that rubber band ramps or moving hoods were inefficient but if you asked me to explain why I’d be lost.
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Wow, fun fact of the day. Who would’ve thought sand actually increases friction when I would assume the opposite effect (try walking over sand on a dusting of sand on a smooth surface).
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Hah sand. The only sand we have around here is that white freezy sand that falls from the sky and then mysteriously disappears whilst leaving the ground moist.
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In my opinion one of the best ways to do a ramp like the one originally described would be to have the bottom part made out of metal, and covered in grip mesh to reduce backspin. Then, we have a reasonably taught rubber band roller spinning at 600-1200 rpm. This has worked pretty well for us, but it can probably be improved.
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Thanks for the posts about the hysteresis and elastic stuff guys. Very interesting read.
@7686B_Ian my ramp is done very similarly except with a lexan backing piece from one of the TP flags and it has caused me no problems either. Like you mentioned, it might be possible to improve it, but I don’t know how since I never tested any other design.
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