a few recent updates... 1. I was having a problem with J5 accuracy due to deflection of the lead screw guide rods. In an attempt to improve this I replaced the guide rods with a THK linear rail fixed to the aluminum housing. It definitely stiffened up that area. Next on the list is an outboard support bearing for the J6 housing but that project is waiting on parts. 2. Picked up a cheap wire feed welder and dismantled it for use on the AR. There's still a lot of work to get it integrated and minimizing the affects from dragging the welding cables around. Hope to have some welding videos up after the holidays. Redlunn

Now that the weather is getting cold, it's time to get back in the shop and work on the AR3. Recent updates include reworking the spline logic to use a Bezier curve and smoothly transition between different end effector orientations while travelling the spline. The video below shows a simulated weld profile with an elliptical weave and continuous spline all the way around the tube. This spline consists of 8 teach points. Someday I'll get an actual welder on there but the pencil pointer will do for now.., Redlunn

Hi Joseph, My build is using the CUI AMT21 "multi-turn absolute" encoders which communicate over RS485 network. Despite their name, these encoders only retain absolute position for a single turn, the turns counter gets reset on power cycle. I am using them with the encoder power hooked up to battery supply to retain the turns count. I was unable to find a true multi turn absolute encoder that appeared feasible to implement with the AR3/4 mechanical design. Of course, if you can mount the encoder to the joint rather than the motor, then single turn absolute would be sufficient. Redlunn

dedoky, My current project can be download here: https://bit.ly/3m7b7HR Redlunn

Back when I did my AR3 build, all of the parts of the stepper kit were also available individually (and it was $25 cheaper to buy them individually). If there is only a part or two that is holding up the kit you might be able to get everything else and get started on your build.

Is there an encoder wiring change due to the teensy 4.1 being non 5V tolerant? Or does the breakout board have that protection built in?

Just for fun I ran the same spline profile as the last video but much slower and added a 4 mm elliptical weave, as if it was running a mig welder. It looks like it could actually work. This is one advantage to running the reverse kinematics in real time on the Teensy 4.1. Hopefully I'll get a change to turn it loose welding for real, maybe this winter. Redlunn AR3 Spline Weave

My robot arm has been dormant for a few months but recently revived to test some new spline interpolation programming. I wanted a way to smoothly navigate through a series of points and a spline seemed like the easiest way to handle the route planning. The points get entered similar to how an arc is entered, with a beginning point, mid point, and end point, but with the spline you can enter many mid points. The speed at the gripper is constant along the path so I'm hoping it will work for some welding applications I have in mind for future projects. AR3 Spline Interpolation

I tweaked some of the core motion profile logic without proper testing and the J4 encoder paid the ultimate price. On the bright side, I did manage to find and fix the issue I was working on.

The reverse kinematics on my robot seem to have a hiccup when moving across X=0.0 during a linear move. When solving for J1 angle, I think it should be using X/Y from center of spherical wrist instead of end of tool. Doing this and using atan2 seems give the expected results. Redlunn Edit: Added image showing how Quadrant is based off X/Y, which affects the J1 angle.

Hello Erik, The multiturn absolute encoders from CUI, such as the AMT212D that I used, have one serious fatal flaw, they aren't really multi turn absolute. At least not by my definition. They are more like single turn absolute with a multi turn incremental counter. The turns count resets to 0 at every power cycle. This functionality was not clear from the datasheet but I did confirm from CUI that the turns count is expected to reset. And I found the following note from a press release on the multi turn feature... "These features provide users with the ability to keep track of position even during power down conditions, while the turns counter can be maintained via a battery backup, eliminating the need for a homing sequence" So, they would work fine as a joint encoder but motor mounting would require battery backup to really work without homing. The RS485 transceiver that I used is the MAX3486ECPA+ https://www.digikey.com/en/products/detail/maxim-integrated/MAX3486ECPA-/1702117 Redlunn

Over the weekend I managed to get 5 of the 6 encoders wired and communicating. Just a little more wiring time and if all looks well I can begin the process of integrating the absolute encoders into the full robot program. Attached is my current program for testing the encoders, which I've been running on a teensy4.0. Edit: removed file and replaced with link to google drive so the latest version is available. http://bit.ly/3pmM7MM

I have the 6 absolute encoders installed but not wired yet. I hope to get that going this coming weekend. Once that is operational I can test the sprocket change. I don't expect much issue with the ratio change, it should be 50% increase in torque with 33% reduction in peak speed.

Well, I'm committed now. All encoder and home switch wiring has been removed. Also finished the J3 sprocket ratio change.

I've now added a second RS485 multi-turn encoder and can read both at over 1000 Hz so 4 more have been ordered to complete the project. The wiring on these encoders is unfortunately tedious (and small) but I think it will pay off in the end. The code is fairly simple and the wiring savings is significant. I'll post an update once all 6 encoders are active. Redlunn

It took awhile but I now have one multi turn encoder communicating on an rs485 bus with a spare teensy 4.0 I had handy. The encoders are half duplex so the transmit and receive takes place on the same wires. At 2mhz there isn't much time to switch between transmit and receive. I was unable to find any sample code or libraries for this task so it had to be developed from the data sheet and experimentation. Next step is to add more encoders to the bus. Once that works then the encoders and code can get moved into the robot program. Redlunn

I have 2 updates planned for the next few days, now that my parts have arrived... First, I will be testing 2 multiturn absolute encoders (CUI AMT212D) which communicate on an RS485 bus at 2 MHz. If it works as expected it should allow removing the encoder and home switch wiring and replacing it with a 2 wire bus which will daisy chain to all encoders. The second task involves some mechanical rework. The J3 joint seems to be the weak point for load capacity and the easiest solution I see is to change the upper chain sprocket to a part with more teeth. I have found a 20 tooth sprocket will fit in the 3D printed housing and should allow for 53% more torque at the joint. A side benefit is the reduction of apparent backlash from the J3 stepper gearbox. I will update with results but I won't get much testing until the encoder experiment is complete. Redlunn

The current status of my project uses a modified version of the ARCs software to send move commands (rather than axis positions) to the teensy. From there the teensy plans out the axis positions. I suppose the move commands could come from anywhere, including the SD card on the teensy if you wanted to run without a PC. The code is in the middle of a major update right now with switching to multiturn absolute encoders on RS485. No more home switches, yay!!

The main issue with the Teensy 4.1 on the AR3 is that it is not 5V tolerant like the Teensy 3.5. So you have to reduce the voltage of encoder signals and possibly the limit switch inputs. Other than that it should be a drop in replacement (though I never tried running the original AR3 software on the Teensy 4.1). I guess I would recommend sticking with the 3.5 and getting everything working then possibly upgrading in future. I'd be happy to share my program with the community but it is missing some key features to really be usable. Primarily the ability to store, modify, and run through a sequence of commands. My goal is to get the motion control side of the program able to run the robot through all necessary motions first, then work on the command system.

An additional difference that I forgot to mention is that the robot is running in "true" closed loop position control, so the motors do whatever is necessary to satisfy the encoders. A new feature since my last post is using the PS3 controller's accelerometers and gyroscopes to adjust the yaw/pitch/roll by simply moving the controller. Here is a video showing how some of these features work. AR3 Robot Custom Program V0.2