View Full Version : [Question(s)] Just Received WidowX Arm

12-07-2012, 11:32 PM
No messages in the Arm Forum?

Has anyone reading this purchased a WidowX arm (or one of the other arms, for that matter)?
Just received mine, but after inventorying parts (and comparing to the installation instructions and parts list), I am missing the three "Wrist Rotate Brackets".
Are the instructions in error, or did they just forget to put them in the box?

Also, I was hoping that someone here could comment on their experiences with control software for these arms.
I am quite experienced at control of multi-axis robotic arms (mostly commercial units that come with substantial software support libraries) and if necessary can write some inverse kinematic routines of my own (which I can share), but would be interested to hear experiences of others. If not experience with Trossen arms, then at least with the Dynamixels!


12-08-2012, 12:00 AM
Hello! We just opened the Arms forum so you're the first thread.

They should be included within the gripper parts bag. If they were not included, please email us with your order # and we'll get them sent out to you ASAP.

I will be posting some example code for the WidowX by Monday at the latest. Please check back on the product page for the download link then.

12-08-2012, 08:27 AM

Not sure if it would help much, I don't have the WidowX Arm but instead have a PhantomX Arm. I have done some playing around with that arm, which you can see more details about in the thread: http://forums.trossenrobotics.com/showthread.php?5689-Kurt-s-PhantomX-Reactor-Robot-Arm

As part of that, I have also around with some software for it, which is up on github\kurte which is mentioned in the thread.


12-08-2012, 08:54 PM
OK, thanks for the info.
I will be watching for the code posts (and maybe providing some of my own in return).
There are some plastic plates in the gripper bag, but they do not correspond to the images shown on the parts list accompanying the assembly instructions (on the web). I will soon find out whether things line up!
[Edit 12/9/12: they do not]
I have found a few other discrepancies with the instructions and parts lists.
Fortunately, I have a reasonable stock of common parts (M3 screws of various lengths and such).
I will post more once I get further along in the assembly process.
Update 12/9/12
Assembly is finished.
The three "Wrist Rotate Brackets" shown in the assembly instructions are indeed necessary and are indeed missing from the kit.
The parts list states that two "F3 Brackets" are required; these are in the kit but are not actually required.
Hopefully Trossen will send me the missing brackets soon.

The kit is quite nice.
One surprising aspect, however is the amount of backlash in the MX-64 servo gear train.
The other servos have little to no noticeable backlash, but the MX-64 backlash translates to about 3mm at the end effector when the arm is fully extended.
Is this typical for these servos, or is this one especially bad?

12-10-2012, 12:10 PM
You have my sincere apology for the missing parts in your kit. Your arm was literally the first one sent out and among the madness of the holiday season it looks like it was not packaged correctly. We're putting in additional verification steps in our kitting processes so that this will not be a problem in the future. We're shipping out the missing parts via 2nd Day Air, should arrive to you on Wednesday.

The backlash you see in the MX-64T is normal. Most Dynamixels are like this (the main exception being the MX-28, which has surprisingly little backlash). This can be offset a bit at the cost of 'smoothness' by setting the PID parameters in the startup section of your code. Simply adjusting P is a good start.

I haven't completed the changes to Kurt's code for the WidowX 100% yet. You're welcome to test out the WIP, but be warned there is a slight bug on startup where the arm has an initial jerk: http://pastebin.com/1Hc18nqs

12-10-2012, 02:18 PM
Thanks very much for the quick response!

12-10-2012, 03:08 PM
Question- were there any actual bolts/nuts missing from the kit or just the wrist pieces? I can get those sent over if so as well.

The F3 brackets are indeed optional, they're intended to give you a mounting surface on the wrist-rotate and gripper servos.

12-10-2012, 05:56 PM
There were no missing screws, but there are a few steps (maybe 3 in total) where the screw size specified in the instructions was not quite appropriate. Also a few inconsistencies in the instructions; for example spacers for middle base -- image shows 3 spacers for each standoff, but instructions state 4. While on this subject, using two standoffs and three spacers (washers) to provide proper spacing between the 2nd and 3rd bases seems like a kludge (and also detracts from the appearance). Since the desired distance is 37.4 mm (very close to 1.5 inches), I would actually prefer to use a single 1.5" standoff.
These are relatively minor quibbles and in general, I would rate the kit as fairly well designed and the arm looks nice once assembled.
I think that there is a clear need for more info on the controller and software, though. It was very unclear whether the Arbotix board had been programmed (and if so, with what firmware).
I strongly suggest that Trossen supply enough info with the kits to allow a quick and easy "checkout"; for example a very simple program to exercise basic functionality.
Oh, and I did in fact use one of the F3 brackets to mount the gripper assembly (90 degrees to standard orientation), but would prefer the in-line orientation allowed by the wrist plates.

12-11-2012, 12:42 AM
OK, I have played around with software a bit (so far, mostly PyPose).
Here are the robot's first baby steps:

12-11-2012, 05:16 PM
Another item that should be in the instructions is a note about what position each motor shaft should be in during assembly.
I went back and adjusted all of them to more reasonable positions after I started exercising the system via software, which was a real pain. It's nice to have the shaft in the center of its range when the axis is in the middle of its move range.

12-15-2012, 01:22 AM
Today I received the missing parts (i.e. wrist plates) for proper in-line installation of the gripper.
Looks much better and this will be a better configuration for my intended application.
The 90 degree mounting I was forced to use previously may be better in some applications, however.
Now I can proceed with software for my application!

12-18-2012, 04:33 PM
I actually kinda liked how you had it mounted at 90 degrees by default.

12-19-2012, 11:46 PM
True -- it would be advantageous for certain applications.
Here is what my gripper looks like now:
I will post a video soon showing this picking up microtiter plates.