I recently did a quick comparison between the automatic calibration and a laser measurement of the anchor positions (link to test). From what I can see, lower calibration current threshold seems to improve accuracy — possibly because of reduced flex or stretch in the system?
As discussed in this thread, belt strech might be a significant contibutor to overal machine accuracy.
If it’s of any interest: I have access to a universal testing machine with an extensometer. If there’s no official data from the vendor, I could try to measure the belt stiffness — provided I can get a piece of spare belt.
I’m also curious if the belts permanently stretch after cycling for X number of times. I know bike cables and chains will do that and have a break-in period. Would love to see the overall length measured from a new belt, run a bunch of loading cycles, then measured again.
I’m going to start by measuring the stiffness first. I’ve never worked with belts before, so figuring out how to grip them properly might be a bit tricky — but definitely doable.
If that goes well, then I will try to run some cycles and see how they behave.
To grip them maybe you could use the belt end that the machine uses on each end, that would give you a nice place to attach a bolt or something like that
I bought the brown fiberglass infused belts to test against the white ones with the metal (that came with the machine). I would think metal stretches more than fiberglass… But jury is out?
I 3D printed a set and that’s what I’m doing with my janky elongation measurement.
@bar Looking into different types of belts, did you try or look at the Gates belts for the M4? Reading various forums some people mention that belts similar to what we use stretch a lot compared to other brands or types like fiberglass reinforced. Curious to test these Long-Length PowerGrip™ GT™2 Linear Belting | Gates Corporation
I did look into some different options and I found the steel reinforced ones to be the best (although they aren’t used for 3D printers because they can’t bend around a small enough radius).
That 100% does not mean that they are the best possible belts. I bet that there are some better options out there that we could find with more research!
Cool. I just ordered a small section which should get delivered tomorrow so I can compare the two this weekend. Fingers crossed that they function better because that would be a very easy fix!
I need to double check my testing setup this weekend, but so far it looks like the belts we use stretch quite a bit. I’ve bolted the top into a massive door header which should’t move at all, then I’m loading the crane scale at the bottom with forces I’ve observed live on the frame with a tensioned M4. I do want to put a dial indicator on the top to make sure my mount isn’t flexing (like another forum member did) so I’ll do that this weekend before posting my results.
Definitely more janky than @Lais’ extensometer machine!
I was contemplating if we could switch to aircraft cables instead. But it would require a redesign of the magnet idler and probably metal components to not wear under the friction of cabling.
I wanted the gates belts because eif my research. But I couldn’t get them to Canada economically. I haven’t tried these yet, I was going to do a stretch test comparison first to see if it was worth switching…but I haven’t got around to it yet
That 100% does not mean that they are the best possible belts. I bet that
there are some better options out there that we could find with more research!
the other thing with steel belts vs kevlar belts is how well they handle the
small radius bends around the encoder wheels. These aren’t super small radius
(not like 12-tooth gears) but the steel will fatigue sooner.
I was contemplating if we could switch to aircraft cables instead. But it
would require a redesign of the magnet idler and probably metal components to
not wear under the friction of cabling.
the bigger problem is accurate measurement of the amount fed out.
friction wheels aren’t reliable, the belt teeth give us accuracy.
not done yet, but we arrived uninjured, but not intact. we ended up blocking 4
lanes of freeway at lunchtime when we had a tire blow on the van, swerved across
5 lanes of freeway about 4 times before spinning out with the 24’ trailer at
right angles to traffic and the van pointed to about 5 o’clock (the hitch/ball
part is twisted quite a bit)
I have to fly back to LA and get my car and little fold-up trailer and then get
the two 16’ pods delivered an unloaded before we are done.
but we are here, as I said uninjured, and my mail server is up and running
again.
