Guidance for Bottle Handling system.

@Robin2 I get you. I give up stepper motors. Just one last thing. In the following sketch you suggested:

|500x462

I understand I will be using springs to make arms retract (otherwise the number of motors will just double).

But for even 5* turn the axel on which string is wound will have to turn several complete turns & then some degrees. As I really don't have experience with servos- can I ask them to perform 2 consequtive 180* turns to get a full turn or do they reset after 180* (I saw them resetting in some Jeremy Blum video).

EDIT

Got continous rotation servo here at https://www.sparkfun.com/products/9347

Thanks @Robin2. Will upload the code samples soon.

I'm not trolling, if it appears that way I apologize.

But yes, I'm trying to get your attention.

Don't use string, at least for the gripper that is - use a Bowden cable setup.

Google it.

carmenLongoria: But for even 5* turn the axel on which string is wound will have to turn several complete turns & then some degrees. As I really don't have experience with servos- can I ask them to perform 2 consequtive 180* turns to get a full turn or do they reset after 180* (I saw them resetting in some Jeremy Blum video).

I don't understand this comment in the context of my diagram.

In my mind the only servo that needs to turn more than 180deg is the one which rotates the whole system - and I did not include that in my diagram.

The flexible "push rod" that I have in mind is the sort of thing that is used in model airplanes - one low-friction plastic tube sliding inside another. It can push as well as pull but could probably exert more force in tension. You can also have "wire in tube" versions.

I understand I will be using springs to make arms retract (otherwise the number of motors will just double).

I don't understand why you think you would need twice as many motors.

Servos can push as well as pull. It might be useful to use a spring to counterbalance some of the load.

It might be wise to use a spring to close the gripper so that it would not let go by accident. The servo could be used to open the gripper against the force of the spring.

...R

here is a link to a page with a lightweight arm.

http://www.robotarm.eu/

if you have access to mill and lathe, you can make all these parts easily.

these are pretty small steppers, probably in the hobby range and usable with a A4899 driver that is easy to use with an Arduino. see Robin2's good intro.

if you were to try to pick up a gallon milk jug, a heavy duty stepper could move much faster and lift the weight. however the aluminum arm might bend.

Robin2 does make a point that steppers are usually 'homed' to a starting point with an end-switch and from that point, all work is based on that reference. but that task is minor.

if you used the vision thing as shown, then all of that is irrelevant. the sensor eliminates any need to monitor motor activity.

I would consider the can grip. a stepper with a screw could crush the can. probably much better to use a hobby servo to eliminate damage.

Robin2 does make a point that if you wanted to try to make a stepper act like a hobby servo, you could, but would need to add an encoder.

I am not sure why there is such a desire to mis-use a stepper and try to make it into something other than what it does best.

if you put a stepper on the arm, home it, then move 'x' steps, the arm will move 'x' steps repeatedly for hours on end. if it hits a brick wall and the arm does not flex, then it might miss a step, or even 100 steps. but that would mean a lot of things gone wrong.

poor design poor assembly poor operation and maybe improper selection of parts.

https://www.youtube.com/watch?v=4KpNEhBRcVM

to start and get a feel for the motion, here is one with hobby servo's

https://www.youtube.com/watch?v=gfsLu1iuLRg

what no one mentioned is that industrial servos are the step up above steppers. they have a VERY large motor, into numbers of horsepower, not fractions. They

have external encoders, and a very complicated driver. used on high-end metal working machines, laser tables, large milling machines, work centers etc.

I would probably limit steppers to something smaller like a Bridgeport mill.

spend some time on youtube and watch what others have done. pretty neat stuff lots of hobby servo types: https://www.youtube.com/watch?v=B2fl8-L6xcA https://www.youtube.com/watch?v=gKKWUZeyAac

if normal operation made a stepper based system miss steps, tehn this would not work https://www.youtube.com/watch?v=t7cGbLSnN78

here is a CNC mill that is retro-fitted with steppers. will run for hours without missing steps while cutting metal parts.

did I mention run for hours without missing steps ? https://www.youtube.com/watch?v=auNZ1gFoMms

I am not sure what the Arduio community has such a poor understanding of steppers in general.

Got continous rotation servo here at https://www.sparkfun.com/products/9347

torque: 66.7 oz-in.

==================================

poulou steppers

https://www.pololu.com/product/1478

holding torque of 19 kg-cm (270 oz-in).

===================

here is a decent motor for a good price http://www.mpja.com/Stepper-Motor-Assembly-NEMA-23-53V/productinfo/17461%20MS/

==================

do the basic math. the answers will reveal themselves.

dave-in-nj: here is a link to a page with a lightweight arm.

http://www.robotarm.eu/

if you have access to mill and lathe, you can make all these parts easily.

I am not disputing ANY of this.

I'm just saying it would take more of my time than ordering some servos from HobbyKing or wherever.

...R

Got a PM just now from a user suggesting that I "don't seem knowledgeable", that is, specifically re. this thread.

It went on a little bit more in addition.

Anyways, I'm out.

Sorry if my approach clouded the message(s).

1:1: Got a PM just now from a user suggesting that I "don't seem knowledgeable", that is, specifically re. this thread.

Having looked back at your posts I don't see that there was any need for that. If anything there was the appearance of "too knowledgable"

And if someone wanted to be critical why not have the courage to do it in public. I would not respond to a PM like that unless I felt I had overstepped the mark.

...R

Thanks a lot @Robin2 & @dave-in-nj, I am currently getting my mechanical feasibility checked by faculty -- and would be obliged to include your names in my Acknowldgements section.

So if you don't mind kindly mail me your names with something like profession . . . I don't know or else if you want I would simply refer you as user @abcd from arduino.cc forums (except it just doesn't look very good or formal in project report file).

If I run into problems, I might ask for guidance again. Thanks once again :)

For my part you may refer to me as "@Robin2 from the Arduino Forum (forum.arduino.cc)"

Thank you for thinking of mentioning us.

...R