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How do we want calibration to work for bottom feeder

I’ve been working on updating the calibration process for the new frames which use the “bottom feeder” approach where the chains feed off the bottom of the sprockets to the sled.

Overall I think it’s a great change. The chains are kept in plane, and they are stored along the top bar which keeps them out of the way.

The trickiest part seems to be how do to the calibration process, specifically the step where we use the chain to measure the distance between the motors.

In the past the chain fed over the top of the motor and then to the top of the other motor which worked well.

When feeding off the bottom it’s a little harder because the chain ends up crossing itself.

Does anyone have a clever solution?

Here are some pictures to clarify what I mean:

The issue only happens during the calibration process, not when cutting.

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My first thought is a s like, bicycle derailleur to get the chain to feed out of the way and drop downward again.

Thank you

In the calibration routine, I tried to write it so that the chains would still feed on top for that measurement. It would be a little awkward, but I think the simplest approach would still be to have the chain on top. It’s only for that one measurement anyway!

I was worried that the chain would be prone to falling off one/both sprockets if put on bottom.

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If you look at the motor-to-motor measurement as a separate first step, then doing that step ‘over the top’ is the best way. True that one then needs to zero the sprockets again and re-rig to do the chain calibration for the bottom-feed orientation, but maybe that’s not a big deal.
Another approach is to do the motor measurement and first part of the chain calibration as before, and paint the ‘king links’ before going on then re-rig as bottom-feed, placing the painted links back onto the top-zeroed sprocket teeth. That’s what I’ve been doing, but it’s more complex than the method above.

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Ok, sounds like a plan.

Let’s go with doing it the same way we have been, then resenting back to zero and working from there.

Thanks for the advice!

I think the answer is to do the measurement between the motors over the top,
then remove the chain entirely, move the motors to the starting position, and
then feed the chains around the bottom.

just because they will be around the bottom to hook to the chain doesn’t mean
they need to go there for the measurement.

it may even be faster to zero the motors (to some multiple of a link and reset
the encoder position, not run all the way back to zero) and run the chain out
again than to retract it the right amount.

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bottomfeeder

:nerd_face:

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That’s the ‘king link’ approach, the same as ‘Manual chain calibration’. It works very well, saves a lot of time.

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Sorry to have to revive this old conversation (not sure if this is the place to ask this), but I am trying to set up the Maslow for calibration for the first time… this thread appears to most likely answer my question. I just completed the distance between the motors. I am now trying to figure out how to set it up to bottom feed. If I follow you correctly, you recommend marking the chain at the top sprocket and then flipping it around to go feed under the motor in the opposite direction? Please let me know if I am reading that correctly. Thank you for your kind attention.

Zach

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Zach,
Some of the info here is old, please take a look at the wik.How To: Get Calibrated!

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Excellent! I will start again in the morning with that. Have a beautiful night!

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