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Ed3D
I can appreciate both sides of what you two are saying. No the deflection isn’t great, neither is repeatability and it could easily be much much better using machined Al but then its no longer this cheap to build. I think this poises itself in a certain price to quality level that many might find appealing / fun.

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Trakyan

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MKSA
5mm flex for 1kg, I don't call that rigid.

Don't used a 1kg print head? The flex should be fairly repeatable so it could be calibrated out with bed leveling (look at scara arms). Of course it isnt as constant in the z axis like with scara but for reasonable z axis ranges it should be "constant enough". At this scale you're likely working with big nozzles, layer heights and extrusion widths. +-1mm may not be too bad.

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MKSA
5mm flex for 1kg, I don't call that rigid.

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DaGameFace


Um, no. I already have a big build volume, the holding torque, lift capacity and high precision are all guaranteed side effects of using screws, even better with ball screws, (I didnt promise high accuracy, which is different) And as for cheap, you let me know when you find an arm that can lift more than 1kg for a reasonable price.

Obviously calibration needs a zero position, endstops are an easy addition, but I also intended on adding encoders on the main joints of the arm.

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MKSA

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DaGameFace
....
PROS:
+Big build volume
+Great holding torque and lift capacity
+High precision
+Cheap to build

CONS:
-Calibration requires accurate measurements of the distances from pivots

Frankly, to achieve the 3 first PROS goals, quality materials, tools even a machine shop and the expertise to run them are required. This is beyond the capacity of the vast majority of 3D printer hobbyists who have difficulties computing steps/mm, use a tap and a caliper. Of course forget the cheap.

Regarding the calibration aspect, it is even more than what you wrote, you have to consider that the step/mm of the head displacements varies as they depends on the arm position. The arm actuators zero must be determined accurately and can't change.

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DaGameFace
....
PROS:
+Big build volume
+Great holding torque and lift capacity
+High precision
+Cheap to build

CONS:
-Calibration requires accurate measurements of the distances from pivots

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MKSA
I fail to see the advantages of the way the lead screws are mounted considering the extra complexity (although the math is done by the microcontroller luckily current 32bits can do). Each joints mean play and there are plenty.
As for rigidity, repeatability, accuracy I wonder even for a FFM 3D printer.

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MechaBits
Yeah I thought it was way over built too...maybe he's planning on relocating it, thought the camera was overkill for in a shop too.
More money, skill & time than sense or something for the real pro market?

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MechaBits
you might like this one [www.facebook.com]

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Ed3D

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DaGameFace
Anything specific you have in mind for the arm?

Nope, just a really cool project. Im sure I can find some kind of use for it though! Perhaps an auto print remover? What are you planning to use it for?

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MKSA
In fact, it is kinematic of a crane [autoline.info] just the leadscrews are arranged in a more complex way than the hydraulic actuators (that could be replaced by ball screws actuators BTW)

Can you give the equations of the X, Y, Z as functions of the three motors steps ?

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DaGameFace
Anything specific you have in mind for the arm?

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jamesdanielv
is there a way to make it use belts? this design seems rigid ,but how fast does it work. a good example would be to have it pick up and pace several items repeatably. is there a homing process that can make the device be ready and generally calibrated within minutes?

also it seems the only thing holding the motor arms in place is the rods that are connected to the motor shafts. is this good enough to hold the weights?

this is a cool design concepts, just wanted to have thought out there about how to have it in real world applications. 1 repeatability, reliability, ease of use.

belts would increase reliability and reduce wear and other issues.
reducing strain on motors from a bearing system than handles load and strain
homing system that can self calibrate in short time, and a math table for users to setup calibration for first time use.

these are just some of my opinions, it does look cool.

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DaGameFace

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LoboCNC
What are you planning on doing for wrist joints, if anything? In designing robot arms, you typically start with the wrist joints and then move back towards the base, as each joint will have to deal with the mass of the more distal joints. The wrist joints are also typically more challenging to design in order to keep the mass and size to a minimum. One more consideration is that the speed of many motions is often limited by the speed of the wrist joints, which often have to go thru very large excursions to reorient parts or reorient to a new grasp orientation.

Im aware that I did the process a bit backward but I needed to test the new(?) idea of linear screws before i dumped time into designing more traditional joints. But luckily I am not constrained in weight much at all since 2.5 lbs of lift can go a long way in a wrist and still have a healthy amount left over for an object to be lifted. Right now im considering just adding a 4th axis to the end to be used a 3d printer platform but a 5 axis gripper could also be really neat. You happen to have any suggestions? Id love to hear them, I'm still in pretty early development.

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LoboCNC
What are you planning on doing for wrist joints, if anything? In designing robot arms, you typically start with the wrist joints and then move back towards the base, as each joint will have to deal with the mass of the more distal joints. The wrist joints are also typically more challenging to design in order to keep the mass and size to a minimum. One more consideration is that the speed of many motions is often limited by the speed of the wrist joints, which often have to go thru very large excursions to reorient parts or reorient to a new grasp orientation.

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Ed3D
I would recommend switching out the lead screws for ball screws. You can get them cheap from china (link)

Second im not sure those couplers are good - switch them out for some of the more rigid style ones not the sprung ones.

Im really interested in this project - any plans to make it available to other people?

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o_lampe
Interesting design!
On first glance, I see the weakest point in the leadscrew nuts. They are too short and any wear in the thread would lead to binding ( on the screw or the slides )