Hey! This thing is still a Work in Progress. Files, instructions, and other stuff might change!

uStepper Robot Arm rev. 2 - Obsolete (See summary)

by nic6911, published

uStepper Robot Arm rev. 2 - Obsolete (See summary) by nic6911 Mar 7, 2016


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Revision 3 is released: http://www.thingiverse.com/thing:1774473

This is 2. revision of my uStepper Robot Arm design (http://www.thingiverse.com/thing:986224).
Visit www.ustepper.com to read more about the controller used for the arm.

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Beautiful progeny
I can not find the track list
thank you

Hey, where are all the files? I can't find them on your github.

Yeah. We have moved a little on the Git repository to make it more consistent. Here: https://github.com/uStepper/uStepper-Robotarm

How can I change the size of some parts ? such as the circle of end 1.

You can edit the iges source files available on the Git repository. But you will need compatible CAD software to do so.

I use CAD 2014 and it can not read the files (from Robot Arm ver1)

How do the improvements come along?

I have been busy lately, so they are on hold for now - but I will look into them when I get the time to do so.

I'm done assembling mine (except for one size of ball bearing I don't have on stock and the missing electronics.)
The list of suggestions for improvements in my Blog posting is complete.

Hi Marcus.
I will have a look at you blog once I get the time, and of course take you suggestions into consideration when updating the material!

Where does the 5th M8 washer go?
Step 27 uses 3.
Step 31 uses one, then it's dismantled and re-attached in step 35.
I can't find any step that uses the the last one.

What bolts to use for step 13+29+31 ?
The walls alone are 8mm thick and the bolt has to sit comfortable in the NEMA17 motor.
But the only M3 bolts we have >=12pcs of are M3x8mm.

but there are countersunk holes in those walls?

thanks, I didn't notice the width of the holes.
I guess the bolts must have flat heads with a most 5mm in diameter like the others?
(you're never specified the bolt type and all I could get in that length are countersunk ones)

"Fig.1: Fit the 608Z bearing in the base gear."

There is no "base_gear.stl" or anything similar.
It looks like "Gears_bottom_edited_plus10.stl"

Hi. Yes, I thought it would be possible to recognize the gear from the pictures in the instructions, maybe I was wrong...

Should I enter my findings regarding assembly instructions as an issue on Github or report them here?

If you just write them down and report them to me, could be as a PM in here, then I will adjust the instructions.

I just cut the rods down to size and am leaving for EasterHegg.
What is the status on the CAD files?
(I am planning to record an introduction to parametric, graphical CAD during EasterHegg and planned
on the minor modifications on your design that I need to do anyway.)

Another thing I found in your assembly instructions:

You have a dozen different lengthes for each bolt diameter but your assembly steps don't say what length one should use in each step.

In Fig.36 you speak of "space" as opposed to "spacer". That's why I couldn't find the spacers in the instructions to find out the required inner diameter/shape. (BoM only speaks of the lengthes.) From the BoM alone they could just as well have been PCB spacers.

I got most of of my parts.
Here is m feedback on your BoM:

for the bolts you didn't specify the type of head, so I assumed flat heads.
some of the M3 sizes you specify are no avaliable in any of the German hardware stores and aparently not common sizes , so I substituted longer sinkhole types.
hopefully the length won't interfere with their function.

the rods I only got as 16x1mm and 6x1mm aluminum. Obviously one of them will be their wrong size and either 1mm too thin or too thick.
The exact size you mention doesn't seem common.

None of the washers you specified are avaliable in any hardware stores. Do you have a DIN number and size? Maybe I was looking at their wrong diameters on the shelf labels.

will the BoM change?
are the rod sizes inner or other diameters?

you have specified a very odd collection of nuts and bolts.
Why 3 different bolt diameters and so many differing lengthes?

Where could youpossibly hey washers in sizes like 8.8mm or 15.8mm? Why are the OD diameters important at all?
You have 2 sizes. washers and large washers (for sheet metal) for each metric diameter.

It's still a work in progress, the nuts and bolts can be found at for example Bauhaus. Rod size are outer diameters. That's standard washer sizes!?? go visit a local hardware store like for example Bauhaus and look. It's hard not to have different lengths of bolts in a design like this.

Unterlegscheiben und Karosseriescheiben halt.
Habe noch nie mehr als 2 Größen für das gleiche metrische Gewinde gesehen.

Ich versuche die Anzahl der verschiedenen Schrauben in Designs immer zu minimieren, auch wenn einige dann länger oder dicker sind als unbedingt nötig.
Sonst frustriert man nur jeden und sich selbst im Zusammenbau. (z. B. 35mm und 40mm mit bloßem Auge zu unterscheiden ohne sie nebeneinander zu halten wird unnötig schwer)

Ok, that's your choice how you set up the BOM in your designs. You are welcome to make your own BOM when putting things together. I made the BOM such that things fit. It is up to those who prints and assembles the arm to adjust the BOM if they wish.

I'd like to build one of these.
It's a much nicer design then the one I'm currently working on.
I'm documenting my progress at: http://marcuswolschon.blogspot.com/2016/03/building-ustepper-robot-arm-rev-2.html

How do you handle homing switches/end stops?
As I understand it, the encoders don't provide an absolute position but after switching it on, the arm needs to know what position it is in.

Your connectors at the end of the-whiteboard.com tubes... how are they fastened?
The instructions only tell to push them in but what secures them in place against pulling forces when lifting a load?
The rods are also missing a lot of details. As they are tubes and we want to insert things it is unclear if the named diameter is inside of outside and what the wall-thickness is.

How much can you lift with the uStepper motors/encoders/drivers that you propose in the BoM at what rod length?
(I need to lift 200g plus the weight of my manipulator at the fully extended reach of about 1m.)

Your GitHub repository only contains the STL exports, not the original CAD files.
I guess to add mounts for homing switches, I'd need to modify the original assembly and then export new STL files for printing/milling.

The assembly instructions don't mention what you are refering to as "spacers" and I can't find them in the large photo of all parts nor in the instructions. Sadly there are as many types of spacers as there are types of things to keep apart.

The bolts could use some information on the types of head (counter sunk, ...) and tip as well as information if a longer version can be substituted (without interfering with any other part) for each of the sizes. I has to guess about the tip and wasn't able get many of the sizes named despite shopping at the same shop chain you mentioned.

I have not done calculations on how much the arm will be able to lift. But as you suggest, it depends on the rod lengths and stepper torque, since the gearing ratio is fixed. The instructions are still a work in progress, and a guide for choosing rod lengths and calculating range + theoretical load will be added once I have time to do the calculations and make descriptions for them.

I had a tight fit on the tubes, but if you are lifting "heavy" things, I would suggest that you use glue to secure the ends to the rods.

With regards to the homing, we are working on the code right now. The idea is to slowly move the arm to it's limits (backwards) and sense when it reaches a mechanical limit using the encoders - eliminating the need for limit switches. On the rotating base, this can however, not be accomplished at the moment. I might add an optional mechanical stop to the base to fix this. But I don't think that limit switches is the way to go, since this will make the design more complex and messy from my point of view.

Best regards Mogens

I'm thinking not about a mechanical stop but to add a simple stud to the gears to interrupt an optional optical switch.
just have 2 mountings holes in the opposing frame parts.
approach the stud form one direction and you know your position.
workshops in a 360 degree base too without adding a mechanical stop. thus a 720 degree motion is still possible.

These aren't changes for you to make.
I'm asking for the original cad files to do them myself for my special application.

I'm also thinking of modifying the rod end parts, to allow for cables to control an effector to be routed inside the tubes.

And of cause to modify the end part to have the matching mounting holes forum my existing, special purpose effector in my personal fork.

I just wanted to avoid additional wires and electronics on the frame. But if you would like to do it, you can make a fork on the Git. I will clean the cad files and commit them as soon as I get time.
I actually already have a modified version of the rod end parts (on the 15mm rods) that makes it possible to have cabling for the end effector inside the rods. I have made a gripper with servos and I'm working on another really nice end effector which will be revealed once I'm done with it :)

Just need the time to finish and post the stuff! Hopefully the CAD files will be available sometime during the week. I will send you a PM once I have added them!

How's the progress with the CAD files?
What format do you use? (I can import and export nearly all of them with my Geomagic license)

I have just added source files to the Git repository. There are three files for the gears, they are made in openscad. The remaining parts are located in a file of .iges format.

The one IGES file in the git seems to only be the base.

hmm... I just checked, and the whole thing is there...? - I added a screendump from the cad program where I just opened the file right now.

combined.iges 13.4MB ...aparently my Geomagic Studio only imports the first solid in that file and ignores all others. :/

Did you solve this problem? I can't see why it shouldn't work for you...

No, I can't read the IGES file.
Is there any other cad format you can export?

Next weekend I'll finish building the mechanics.
If all else fails, I'll have to use the feature-detection on the STL files to create parameter-less design files
and then create the assembly-constraints by hand. Then I'll have a starting-point for my modifications.

I'll be on the Easterhegg hacking festival next weekend. So I'll be able to do me modifications then and 3d print, assemble and test them right away.