Not sure…set feed rate in makercam at 30 for all
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I like the theory that this could be a federate issue. A heavy sled near the top could be slowing the motor down to the point that it can’t keep up with it’s target position which would result in the type of general downwards slope we are seeing…then when it gets to the end of the cut it could catch up suddenly and go back to where it should be giving us the jump up we’re seeing there.
I guess the test would be to try at a lower feed rate? We should be seeing that position error showing up in GC, right?
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I would have thought that having an encoder and positive positional feedback would keep it from getting very far off the desired track - or at least giving an error. Would it be hard to automatically slow down based on position error?
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We should always be able to see the error, and you are right that we could slow down or at the very least display a warning to the user. I’m pretty sure we don’t do anything like that right now, but this might be the reason to add it.
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The feedrate in the file that @gero posted was 1000 mm/sec (~40 in/sec). Would be interesting to see if same thing occurred at feedrate of around 20 ipm… at least see if there is a difference.
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The sagging line might be caused by a motor controller failing to full power to a motor due to heat.
@gero, you asked about the thermal effect of different PWM settings in a different thread - were these cuts made with a changed PWM value? I wouldn’t think PWM should have a thermal effect, but that’s another variable to be considered.
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Feed rate vs accuracy over different areas of the work surface is another set of test that would be good to do, especially across the upper regions.
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I had the same issue and I think it was do to the left motor not being able to keep up with right motor. I ended up just slowing the feed rate down and things improved.
I wonder if it has to do with the different PWM clock which should be fixed in latest version.
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Very interesting. I don’t know much about the motors, so I’m taking a stab in the dark here, but it seems that we know the motor’s stall torque, as well as their maximum speed (presumably with no load). The maximum speed versus torque is likely some non-flat curve. I wonder if this is a case of exceeding the speed/torque curve.
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This is at the top of the workarea, so changes of chain slack shouldn’t be a concern.
The bit is wandering in the direction that it would pull if the feed rate is too high, and there’s primarily only chain tension to counteract it. Lower on the board with the chain angles different they can better resist that pull. I think that if the cut were moving clockwise at this high position, the weight of the sled would help resist the bit’s pull and the line would be straight.
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Wow, so much valuable input to narrow it in. Thank you all!
I could convince my boss that I’m not productive on the job and got off till next Sunday, Maslow holidays!
Tests in the making:
- Same weight and half feed-rate counter clockwise
- Same weight and feed-rate clockwise
- Reduced weight (1 brick less) at same direction and feed
and perhaps a combination of some, if those 3 not already show what is going on.
Results in 4 -5 hours from this post.
The log from line 317810 
to 318113 shows Idle,MPos: (x moving left), y at 503.00 where it should be the entire cut. The ‘sag’ seems not to be caught.
No, I only played with the setting driving the sled around without a bit. I love how ‘silent’ it was at 31000Hz but am scared it will fry my chips. The cut was done with 490Hz.
Additional info: I went with a slightly aggressive 4.2mm stepdown on a 6mm 2 flute with ~10000 rpm
Thanks again, Regards, Gero
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Hi,
I noticed on the 4th picture that the linkage kit is in an awkward position. Is there a reason for this?
It doesn’t seem to be in a normal alignment in that the right chain is very far from being pointing to the centre of the router.
Left chain looks better but doesn’t also look to be pointing at the centre.
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Yes you are right, isn’t the linkage supposed to make line of chain intersect with router bit?
I apologize for the confusion created. The sled seems to be resting with sloped chains.
I thought the focus was on the cuts and did not realize the router in the foreground.
Forgive me. The extended dlang top-mount is clearing the handles and functions well.
Sled and top-mount spacer are cnc’d, so my expectation of accuracy in mounting and flex is < 1mm.
Edit: As a reference with the sled hanging on the chains: https://youtu.be/bTDzhK8_5Vs
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I was wondering if the clock change might be responsible as well.
Thank you
I was hoping the change would fix the the problem, I have seen this since day one so I don’t think the latest change is the issue. Please see my video that I made awhile ago. If you watch one of the movies shows the sled move along the top and it slowly goes down as it moves left and suddenly jumps up near the end. In the other video it goes from left to right and stay flat across the top.
https://drive.google.com/open?id=1DdrU9igwtY_A-4fV0ncgpafxgWUIqg-g
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An unexpected visitor took parts of the plans of testing tonight out. He agreed to join some.
- Clockwise vs Counter clockwise mirrors the error.
- Reducing the feed rate makes the top line more straight. Not level from what I can tell.
-Going from feed rate 1000 to 450 made a cut with same weight that does not look bad. Going from 450 to 200 feed rate made a path that is aprox. 0.5 mm above the 450 one, on the ‘straight cut’.
The tests with same feed and less weight are missing tonight, sorry.
My woman is the best, at 1:44 she caught the first attempt. https://youtu.be/w91iHpJyB9A
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Excellent test results!!
It sounds like we are exceeding the speed/torque curve of the motors right up here at the top center. Do we need to force a lower feedrate there? Is there something else we could do?
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This means that the sag is on the right side when cutting clockwise, yes? That would make drag from the bit seem unlikely.
She is, for a fact! Do something very nice for her!
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The weight test will give more feed back I hope. Sadly not tonight, but Maslow holidays. Exploing the exremes means you can always go down to get results 
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