Re: Rostock Mini build and Rostock vs mini questions

February 11, 2013, 10:23 am

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stratmaster458 Wrote:
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> I'm still having trouble deciding what is the best
> bowden extruder for the Rostock mini, and what
> clamp I should use. I need a setup that works for
> 1.75mm filament.


SeeMeCNC Rostock Max uses a 1.75mm Bowden IIRC. Dunno if it would be acceptable for your mini but it fits your filament.

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V-Shaped Delta

February 12, 2013, 6:06 am

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This Thread will be about documenting Concepts/Ideas.....

I am trying to make the Rostock more portable.

Concept #001

February 12, 2013, 6:13 am

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Concept #001


A Stiff V Shape.
By placing the Motors on the outside it could probably be folded in the Center...

Re: V-Shaped Delta

February 12, 2013, 7:07 am

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... here an alternative concept with a really small frame footprint - replace the piezo-motors with linear drives and you have the idea ;)

Re: V-Shaped Delta

February 12, 2013, 8:18 am

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Thx Vic, do we have a TriGlide(is it?) supporting Firmware yet ?

Re: V-Shaped Delta

February 12, 2013, 10:27 am

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... shouldn't be a problem to change the Rostock-firmwares, it's only slightly different calculation for the two angular axes --- here Y+Z instead of X+Y with the Rostock ...

Re: Reprapped delta robot.

February 13, 2013, 4:05 am

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more to this topic
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Counterweight on Rostock

February 13, 2013, 5:27 am

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Does is make Sens to add an Counterweight for every arm, so the motors have the same up and down force?

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Re: Counterweight on Rostock

February 13, 2013, 6:58 am

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Not really as you will then have twice the mass to move, so half the acceleration.

Re: Counterweight on Rostock

February 13, 2013, 7:04 am

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It might, but how much weight is the question. The problem is that the down-force on each carriage changes depending on where the head is, relative to the carriage. As it moves further away from any given carriage, in the X-Y plane, it puts less down-force on the carriage.

In addition, benefits of the counterweight have to be *ahem* weighed against the additional inertia added to the system by adding the counterweights.

All that adding the counterweights will do is increase the maximum acceleration that the platform can use.

[edit: ] Provided, of course, that the counterweight inertia is less than the reclaimed downforce--now that I think about it, this can never be true, so you can't increase the maximum acceleration available by adding counterweights.

Re: Counterweight on Rostock

February 13, 2013, 8:23 am

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... I've seen some systems with a really long spring wired from the head to the ceiling, so the counter-force would be nearly constant over the Z range ...

Re: Reprapped delta robot.

February 13, 2013, 10:30 am

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I think it's going to be difficult to get adequately accurate straight line motion from the more traditional delta layouts,.
I think much of the wobble will be down to the stepper motion.

Re: Counterweight on Rostock

February 13, 2013, 11:28 am

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Its common on conveyor lifters to add a counterweight to reduce the effective mass that is lifted and hence reduce the work done by the motor. Its also common on fork lift trucks. I believe the mass is set to around half the maximum lift weight or half the expected mass to be lifted in the case of a conveyor.

The mass is connected so it hangs the other side of the top roller and assists the lift by effectively counteracting the mass.

Speaking simply and ignoring friction I think you are all partially correct.
If I remember my physics right, the counterweight would naturally accelerate down at 9.81m/secsq (gravity) if unconstrained, so I think it assists acceleration up to that value when the carriage is rising and the counterweight is moving down (above that acceleration value the connecting cable is basically unloaded) so you don't get any benefit.

When the main carriage is moving down and the counterweight is moving up, The counterweight resists the acceleration as the masses are effectively combined..

I could understand there may be a benefit if the carriage is many kilograms, but for a light carriage such as on the delta, the frictional forces are probably the main ones you are concerned with. This counterweight system would be more complex so any benefits you might gain would be hidden by the increased friction of the more complex mechanism.

Viktor does raise an interesting point as there may be some benefit to reducing the Mass of the tool head by connecting it directly to a counterweight or spring. I think you would only see a benefit when moving up in the Z direction quickly. As a 3D printer only does this in small increments every now and again, the benefits would be minimal with current printers.

Its a good suggestion though and one that could be effective on larger machines such as those that they are considering to print buildings.

Re: Counterweight on Rostock

February 13, 2013, 2:01 pm

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Having the belts under tension in one direction like on a Rostock also means that any backlash due to belt/pulley mating imperfetions is minimised.

Re: Counterweight on Rostock

February 14, 2013, 6:39 am

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Greg Frost Wrote:
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> Having the belts under tension in one direction
> like on a Rostock also means that any backlash due
> to belt/pulley mating imperfetions is minimised.

That's only true if your acceleration doesn't exceed acceleration due to gravity.

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Smooth rods and diagonal rods length dimension -Rostock

February 21, 2013, 6:11 am

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Hi

I´m trying to build a Rostock, and i have doubts on the dimensions of the rods and the resulting printing area.
I have 500mm smooth rods, and i wanted to ask how can i determine the diagonal rods length and the resulting printing area?

If possible i would like to get something arround 200x200x200.How can i see if its possible to get this printing envelop?

Re: Smooth rods and diagonal rods length dimension -Rostock

February 21, 2013, 6:37 am

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... you'll get a good estimate with drawing a sketch with one arm positioned horizontal - then the center of the toolhead should be able to draw an arc from one of the opposing struts to the other.

You won't get this far, but longer arms make the bot more wobbly and much shorter will loose the (maybe comming, optional) ability to print 'between the struts' with a rectangular build base bigger than the common circular footprints ...

Re: Smooth rods and diagonal rods length dimension -Rostock

February 21, 2013, 12:02 pm

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Thanks VDX

I shall look into it later on tonight!

Re: Smooth rods and diagonal rods length dimension -Rostock

February 22, 2013, 3:26 am

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I did a rough sketch of how to look at the build area in this post.

I suggest you aim for a rounded triangle, with each vertex close to the base of the closest pillar. That way, there are no points in the travel of any arm that are excluded by mechanical constraints. To do this, you need to set up the ratios so that one arm is completely vertical when the other two are completely horizontal. I can do up the math for you if you want, but I don't have time to look at it just now.

Re: Smooth rods and diagonal rods length dimension -Rostock

February 22, 2013, 11:24 am

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Ok. I have 500mm smoth rods, i did the diagonal rods with 210mm (from center to center of the ball ends) and i can get one arm completely vertical when the other 2 are completely horizontal.

Now i have 410mm where the vertical carriages can travel, so if i´m not wrong i should be able to get something around 150mm of printing height.
I will also do the math to see what i get.