Calibration Process Brainstorming

I don’t think they exist. Back when the triangular kinematics was comprised of just the motor distance equations, this was easy. When we added in motor sprocket geometry, I attempted to calculate the forward kinematics but was not able to solve for them in a clean way. After adding in chain sag I didn’t even try.

You’re absolutely welcome to give it a shot though. Not saying it can’t be done, but it won’t be easy!

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Thanks. I was afraid of that.

Yeah, it is a bit of a pain. I initially wanted to maintain a clean forward kinematics algorithm, but quickly found that as the reverse kinematics algorithm became more accurate (and correspondingly more complex), the forward kinematics equations became hideous. Hence the current triangular kinematics calibration algorithm.

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Another question. Is it ok to create a dependence on another Python module, SciPy? I am not 100% sure about all the implications of doing this.

That’s a good question. I’m new to this project also, so I’m not sure the opinion and implications on additional modules. @bar and others, would you know?

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As long as we can still bundle things up to I think it would be OK. The preference is always for keeping things simple and reducing dependencies, but if there is a module out there that we absolutely need I think it could be worth it.

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it’s probably ok, but check that the result actually makes a meaningful
difference before making it a requirement in the shipped version.

@rjon17469, @bar, and @dlang, thanks for your thoughts.

Right now, we don’t know if the juice is worth the squeeze. It is difficult to know right now, because we have very little knowledge about: the long-term durability of the machine, and how that impacts the need to calibrate and re-calibrate; how many use-cases exist, and their required accuracy; how difficult the idea is to implement and use; etc.

For now, I see calibration as foundational to Maslow, and something that can open or close doors. I am well positioned to do the work due to professional experience. This is something I can contribute, potentially bringing value to the world. It will be slow and uncertain; many things are.

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Sorry for digging this old thread up. I was looking for different ways to maximize accuracy but I might have something to contribute to this conversation.

My method of measuring simply involves a good quality tape measure and two small quick clamps. Instead of measuring from one cut to the next cut, I simply hook the tap on the far left (or right for that matter) side of the plywood at a location that if I pull the tape perfectly horizontal it will cross both cuts to be measured.

Once I find the right elevation I pull the tape out a few inches and lock the lower edge of the tape in place with the small quick clamp.

I then pull the tape to the far side of the piece of plywood trying to keep the tape dead horizontal and again clamp the tape to the plywood with the small quick clamp on the bottom edge of the tape.

Now that my tape is fixed in place across my cuts… I can take my time accurately measuring from the requested edges of the cuts.

This method of course requires you to subtract the short measurement (side of the plywood to the first measured edge) from the long measurement (side of the plywood to the far cut edge requested), rendering you the difference which is the requested length from ground control.

Most woodworkers will have the quick clamps necessary and noobs can get them for \$2.50 each from wal-mart or home depot.

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I use this method too! More math, but much less fuss. Really highlights the benefit of metric measurements, too. I store the clamps clipped th the top of the frame, handy to hold the chain ends when I unhook the sled.
If we has a ‘tip-of-the-week’ category, you’d have my vote

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Haha thank you. There are a couple other reasons that i like this method.

1. Doesnt force you to rely on the slop in the tape measure’s hook. I think measuring from one part of the tape to another part of the tape gives you a more accurate measurement than relying on the hook to be repeatable and calibrated.

2. Holds the tape dead stable so you can take your time and dial in an accurate measurement. Some of our eyes arent what they used to be, so that definately helps holding things still while the eyes adjust.

3. Lends itself well to adding additional cuts to the calibration step in between each of the existing outer cuts to assist building a matrix of measurements so that chain sag can be accurate regardless of sled position.

Im not sure how numbers are interpolated now, but it would be interesting to have a test cut routine with many more cuts to make a matrix of chain sag measurements to maintain equal accuracy regardless where the cut is being made.

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That’s another benefit of your method.

until you damage the tape, the hook is repeatable and calibrated to be exactly
the thickness of the end of the hook (so that inside and outside are the same
result)

I trust that the width of the hook material was the design intent for the movement of the hook relative to the tape measurements… i just dont trust it to be exact when your talking about measurments more accurate than 1/16”.

Also, because the calibration cut depth might not be deep enough to accept the full hook depth, as you try to pull the tape tight you get some angle deflection of the hook that effects your measurements.

Hooking on the side of the plywood eliminates the possability of this deflection.

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So I’m really late to this discussion, but I’ll offer yet another idea. What if the Maslow cut a reference mark on the left side of the sheet and then cut a set of vernier marks on the right side? With a vernier, you can measure better than the resolution of your tape measure over large distances.

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Maybe I’m crazy, as I’m awake way later than I should be and haven’t gone through the calibration process yet, but as I was reading this and an idea popped into my head. Calibration is probably the most intimidating sound part to a noob like myself.

Can the calibration be solved by the Maslow itself, without the need to cut anything? If the Maslow has a pencil instead of the router in place, could it just draw the reference points you need for calibration? Digital image processing should be good enough to calculate all the distances you want from here. It’s done all the time in construction, the guys from Home Depot did it with a few stickers and a digital camera for my new countertops 10 years ago. It was pretty accurate then and those images qualities were far less than what any of us can take with our cell phones.

Stickers on the material edges, the motors, the sled, maybe even at points in the chain when the sled is in each position. You snap the photos, upload them, software magic and you are done. Ship new Maslow kits with the pencil holders too. or a sharpie on a foam spoil board.

Just some food for thought for the people way smarter than me on this stuff.

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