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Calibration issues?

I have read a ton on the calibration, but have a few questions I couldn’t find exactly as I have going on.

First, when using the chain to measure motor spacing, I fed the chain out, connected the two motors by the chain as pictured, and withdrew until there was about 1" sag at the middle of the chain. The pull tight command did not pull the chain significantly tighter. I redid this set and manually made the chain much tighter and ended up with a motor spacing measurement about 10mm less. Should the motors have made the chain taught for the measurement? If not I may repeat and try to make it even tighter.

Second, I am having issues (I think) with the sprocket alignment. In the early steps of calibration I aligned the sprocket on each motor to 12:00. In the later stage of the calibration (after motor spacing measurement) when it asks for the sprockets again to be aligned to 12:00, I hit the automatic button and it did not go to 12:00. Does this indicate something wasn’t done correctly or didn’t save a correct value?

Also, after feeding out chain of 2032mm, the left motor appeared to be back at 12:00, but the right motor was far off. 2032mm should be 32 full revolutions of 63.5mm, so I expected the sprocket to end up back where it was. Is this also an indicator something went wrong? Best place to look to fix it?

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Good deduction of what the right question to ask is. The motors should make the chain tight for that measurement so it sounds like all was well the second time you did it.

I am not 100% sure that button is working right now. I wouldn’t worry about it and use the manual buttons.

I would also expect both sprockets to end up back at 12 here, but I haven’t checked that myself. Its possible for them to end up a little bit off during this step, but they know they are slightly off. The PID controller is expecting the weight of the sled so without it they aren’t very accurate…but the encoder is measuring the true position so that error should be corrected automatically the first time you move the sled

The automatic button doesn’t seem to work perfectly in ground control. I spent a lot of time trying to figure out why, but I think its a firmware issue. Nevertheless, it should get you pretty close… then just adjust it from there manually.

Yes, in my opinion, this is indicative of something going wrong. Note, this assumes you have a stock system (i.e., stock motors, etc.) . If you aren’t ending up with both sprockets at 12:00, then either you did something wrong in the calibration process or something is wrong with the machine. If both sprockets were vertical when you started and ‘define zero’ (or whatever its called) was pressed, and then you fed out 2032 mm of chain, both sprockets should be vertical again. Most of the time this happens is because (this is not meant derogatorily) the user didn’t follow the instructions perfectly.
Which frame did you build? One where the chain slack runs against the top beam?

Review this post and see if there were any missteps…

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Thanks bar and madgrizzle for the info, and the excellent calibration guide. I read the guide over before performing the calibration. I believe I did all of the steps properly, but will rerun calibration sometime soon to see. I also want to cut a file with some known measurements to see accuracy.

My frame doesn’t follow the stock designs, but it is similar. I am using the 12’ top bar sold by metal maslow, and the slack is run against the top beam with counterweights. Here are some pictures.

Nice setup.

One thing you can do to check is to set the sprockets vertical and then hit the 360 deg rotate multiple times (like maybe 10) to make sure the same tooth is getting aligned vertical. If you notice it being off, then maybe some setting is wrong? I assume chain pitch is set for 6.35 mm? Also, grab the sprocket by hand and try to turn it to make sure it’s not slipping.