@erik 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.
Sounds great. I'd love to hear about your progress.
I hope I'm receiving my kit this/next week so I can start building. I have ordered the stepper kit but didn't order encoders yet. I also have a couple of nice beefy Clearpath servo's around which I'm going to experiment with (if I can fit them properly).
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.
Hi Redlunn,
I'm looking into ordering the encoders for my AR3. I think I will follow the same path as you did and start with 6x AMT102 or 103 and also 1 AMT212D or AMT213D. Have you also considered using a single turn version (AMT212B) and directly mount it to the joint as another user is trying? Although after looking at the prices for both versions it doesn't make a world of difference.
Can you tell me which transceiver you used for RS485? I'm not very familiar with RS485 to be honest.
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
Hi Redlunn,
After seeing how the 212D worked internally and after reading the datasheet I somewhat expected it already that it couldn't work the way we want it to work... That's quite a bummer to be honest but somewhat expected.
So the only way to get it working reliable/as expected(i.e. not using endstop switches) is to use them on the joints. But that requires redesigning quite a lot of parts. I think I'll stick to the AMT102/103 for now and just order one 212 for testing purposes until I get the time to redesign the required parts.
But that doesn't mean I lost interest in it so if you make any progress please let us know!
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.
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https://anninrobotics.com/wp-content/uploads/2025/07/AR3-With-Custom-Program_4.avif
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.
https://anninrobotics.com/wp-content/uploads/2025/07/AR3-With-Custom-Program_5.avif
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.
https://anninrobotics.com/wp-content/uploads/2025/07/AR3-With-Custom-Program_6.avif
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
https://anninrobotics.com/wp-content/uploads/2025/07/AR3-With-Custom-Program_7.avif
I was looking at making some of the improvements you had listed, as well as a smooth ramp up and down in speed for accel/deccel. Excellent work so far! I figured I would check in first to see if you plan to release what you have so far.
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
a few recent updates...
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.
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
