New ORD Bot Idea

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Re: New ORD Bot Idea

Postby bdring » Mon Mar 25, 2013 5:57 pm

Nema17 is a motor standard, correct?


Sort of.

In my experience, the holes are usually per standard. The outside dimensions are at or below the standard size. The boss around the motor can vary or not be there. The mitered corners are hit or miss.

I think he is showing the angled slots for NEMA14 as well.
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Re: New ORD Bot Idea

Postby Digitalmagic » Mon Mar 25, 2013 6:02 pm

bdring wrote:I think he is showing the angled slots for NEMA14 as well.

Like you did for the original motor plate...
ORDBot-MotorPlate.JPG
ORD Bot motor plate


bdring wrote:...I think you need to analyse the whole machine...

Of course, and am not skilled for such a complex thing.
I like the idea to compare the torsion levels between the Misumi and the U structure, applying a moment on one extremity.
The U-shape cross-section is 117,103 mm2, while the Misumi HFS5-2040 is 321,216 mm2, more than a 2.5 ratio.
I measure 1.5mm thickness for the U-shape, that's right?

Applying the same 10 lbforce mm moment to one extremity, having the other one fixed, configuring 6061 for both:
The Max displacement magnitude is 0,001906 for Misumi, and 0,1742 for U-shape. Ratio of 91 is just HUGE.

HFS5-2040-370-UShape-Torsion.JPG
Misumi (left) displacement scaled view is magnified around 100 times

Indeed, these 2 are very different profiles, and this part is like the ORD Bot Backbone, sort of.
Last edited by Digitalmagic on Tue Mar 26, 2013 10:34 am, edited 1 time in total.
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Re: New ORD Bot Idea

Postby bdring » Mon Mar 25, 2013 8:23 pm

This overall design will be better than the Misumi version. You are worried about the strongest links. I am worried about the weakest ones.

There are no forces like you are applying. Your constraints and force locations are wrong. The rest of the structure is important and missing. I want a race car not a tank.

BTW: you are using the wrong Misumi extrusion. The one I used is even stronger ;)
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Re: New ORD Bot Idea

Postby orcinus » Mon Mar 25, 2013 8:59 pm

That misumi will have *much* less torsion deflection than the proposed profile is a no-brainer.
You can deduce that from the profile itself just by looking at it ;)

The question isn't which is stronger, the question is which is strong enough.
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Re: New ORD Bot Idea

Postby Digitalmagic » Mon Mar 25, 2013 10:09 pm

Funny! Of course, it is obvious by just seeing it, but the question is how much, like ranking... earthquakes! :)

If the static rigidity of this part, linked to the frame is absolutely no problem, the vibrations can be a problem.
Bart mentioned earlier: "I think this will be stronger than the current design in all modes except for attaching the Y axis assembly"
Because Y-axis is cantilever from the middle of X-axis.
And with a really more flexible part, Y-axis torsion is more potential, possibly inducing more vibrations.

I really don't like the motor plate design (another cantilever), and I imagined using a 50mm x 50mm alu hollow stock, instead, having a thickness of 2mm minimum.
Increasing rigidity can never be a disadvantage.
Finding a solution resolving motor plates issue, while preserving HFS5-2040 rigidity is also a no-brainer.
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Re: New ORD Bot Idea

Postby flurin » Tue Mar 26, 2013 10:31 am

Why not combine Misumi and U-Channel?
I'm using this Motor Bracket for 2 months. It works perfectly for me.
Z-MotorBracket.JPG

http://www.thingiverse.com/thing:43069
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Re: New ORD Bot Idea

Postby Digitalmagic » Tue Mar 26, 2013 10:40 am

The best no-brainer solution, yours, keeping T-slot rigidity and enhancing the motor plate with a lateral binding.

I planned to design alu U-shape motor plate, but now I prefer this printed thing. Just so simple and elegant!
MotorPlate-Bracket.JPG
Low bracket needed to fit upper bracket 44mm width

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Re: New ORD Bot Idea

Postby bdring » Tue Mar 26, 2013 1:48 pm

The drawbacks to a second piece.

1. It requires extra parts and hardware
2. It must be aligned
3. It must be located further away from the vertical extrusion. This affect stiffness of this part and the gantry bracket.
4. Printed parts can warp during printing or over time.
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Re: New ORD Bot Idea

Postby Digitalmagic » Wed Mar 27, 2013 7:05 pm

bdring wrote:1. It requires extra parts and hardware.
If you use the upper bracket only with 2 screws, like the original motor plate, you gain rigidity by the side foldings

bdring wrote:2. It must be aligned.
Just using the upper bracket, same requirement as original motor plate.
Using both brackets, it is self-aligning, because inner dimensions are to be fitting snugly 20x40.
Accurate cnc and folding is critical, though.

bdring wrote:3. It must be located further away from the vertical extrusion.
No, the design have exactly the same footprint compared to original plates.

bdring wrote:4. Printed parts can warp during printing or over time.
Using a bad printed part is a bad idea, and correctly printed ABS won't delaminate later on.
You can also print a partially featured ABS part, and machine it, why not.

To follow the one piece design, I think it makes sense to use a thicker stock, with a square profile.
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Re: New ORD Bot Idea

Postby bdring » Wed Mar 27, 2013 7:44 pm

1. The extra hardware comment was comparing the "new idea" to the previous design and the the other versions of folded brackets and printed brackets.

2. You still have the alignment in the X direction because you are mounting to t-slots.

3. Again this compares to the original design and the other versions of folded brackets and printed brackets. Currently the Z motor is as close to the Misumi extrusion as possible. With the folded u channel, the motor can move a lot closer to the Z extrusions which has many benefits in any design. See the rendering.

motor_loc.jpg


4. When you bolt across the layers it is unlikely to delaminate, but even without warping, the only surface that is truly flat is the bed side surface. A little sanding or machining could fix that.
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