For now, here is a list of features I've implemented in for the current framework:

• Inverse Kinematics

  • X, Y and Z translation

  • Pitch, Yaw and Roll

  • Control through remote's joysticks

• Gait generation

  • Adjustable parameters: 

    • Step size X, Y and Z

    • Yaw angle

    • Swing/ stand timing

  • Combination of any input

    • X and Y translation, Yaw and Pitch rotation

  • Acceleration/ deceleration curves

  • Control through remote's joysticks

• Robot state

  • Height and stance width that adjusts kinematics and gait generation

  • Cartesian position of robot's geometric center and rotational state

  • Adjustable ground direction (with a fully symmetrical robot, like DAGR and Makech, it is possible to "flip" the direction of the ground by negating every calculated result)

• Adjustable robot constants 

  • Link lengths, robot dimensions, offset and reduction ratios

  • Compatibility with any robot by adjusting the constants

Even though all the actuators were designed to be assembled exactly the same, the assembly procedure I followed is a little different between the knee, hip and shoulder. Generally, the procedure is the following:

1. Hot glue the actuator wires right at the body opening to avoid breaking the wires right at this spot from manipulating the part.

2. Cut the actuator's wires to exactly the following lengths, measured from the tangent of the edge of the body:

   1. 1. 1. Red -> 19 mm

         2. Black -> 12 mm

         3. White -> 20 mm

3. Super-glue a diametrically polarized magnet to the 3D printed adapter.

4. Press-fit the adapter to the hallow shaft in the back of the actuator, make sure the magnet does not wobble or looks uneven.
   Note: This is me from the future, make sure to super-glue also the adapter into the hallow shaft, press-fitting cannot take the movements of the quadruped and loose magnets were a huge pain point in the future.

5. Grab an Actuator Back Plate A and populate the M2.5 screws for the shoulder/hip, or populate the M2.5 and M3 screws for the knee actuator. Make sure to use medium strength threat-locker on all screws (I've been using orange Permatex Threadlocker with great success).

6. Solder a 2x4 programming header to the Dagor Controller, straight connector for the hip and shoulder actuators, 90 degree connector for the knee actuators.

7. Cut the respective length of 18 AWG silicon wire for the power input of the Dagor Controller:

   1. 1. 1. Knee -> 350 mm

         2. Hip -> 80 mm

         3. Shoulder -> 280 mm

8. Solder the power wires to the Dagor Controller with the wires coming from the top of the board.

9. Solder the motor phases U, V and W to the Dagor Controller board, red wire being U, black V and white W, with the wires coming from the underside of the board. 

10. Secure the board to the actuator plate A with 4x M2.5 x 10mm screws. Make sure to not over tighten to not stress the board, the screws touching the board is enough.

11. Connect the WiFi antenna to the ESP32 on the Dagor Controller board.

12. Screw down the Back Plate B to the Back Plate A with 7x M2.5 x 16mm screws, make sure the Plate B corresponds to the correct actuator (hip, shoulder or knee). Do not over tighten the screws as the screws thread into plastic. For the knee actuator, do not screw the Plate B, because this plate has to be screw down to the hip actuator first and then screwed to the knee actuator.

After an actuator is prepared with electronics, it has to be further assembled into a knee, hip or shoulder actuator, as it goes into the leg assembly, from now on called J1 J2 and J3 respectively. For J2 (hip actuator), the front flange that holds the big output bearing has to be removed and in its place the J2 Steel Front Plate with a PETG flange is held with 6x M2.5 x 16mm screws. Afterwards the J3 Back Plate B is screwed down with 3x M3 x 20mm screws. All screws should be fastened using medium strength thread-locker. Tape is added to the electronics facing face to avoid a short in case the screws back out.

The J1 assemblies get mounted to the J1 Mount Steel Plate with 6x M2.5 x 16mm screws, there is a PETG shim in between steel plate and actuator, that is held by the same mounting holes, which functions to friction hold the 4x short carbon fiber rods and give structure to the robot's torso. This steel plate has two more 3D printed shims that friction hold the 2x long carbon fiber rods. There is a TPU grommet in the bore in the center of the plate where the power cables come in to connect to the power distribution board. The shoulder actuator then gets the 3D printed J1-J2 Mount fastened with 3x M3 x 14mm screws, this is where the J2 Steel Front Plate gets secured with 2x M2.5 x 20mm screws.

I reached out to SteadyWin (manufacturer?) and purchased 8x GIM4305 and 4x GIM4310. While figuring out the details I inquired about the material of the gears and they confirmed that the gears on the GIM4305 were made of aluminum, while the gears of the GIM4310 were steel. I asked if it was possible to purchase GIM4305 with steel gears and they said that it was, and that they were planing on a release soon; the 8x GIM4305 I bought have steel gears in them. I anticipate that these steel gears will make this actuators last longer. While I would have liked to conduct a stress test, I am currently committed to this design challenge, only time will reveal their true strength.

To prepare for the actuators arrival I have been printing different pulleys to test the new reduction ratio. I cannot afford the length of the tibia to increase a lot because that would mean the knees would collided when the legs are completely tucked in (when the robot is resting on it's belly). I am increasing the teeth of the input pulley and decreasing the number of the output pulley while trying to maintain the distance between them with the same size belts. After a bunch of printing and trial and converged to an input pulley of 24 teeth and an output pulley of 27 teeth, giving the knee a reduction ratio of 1:1.125. I would have preferred to have a reduction ratio closer to 1:1 or a multiplication ratio, but 24T is the biggest pulley that fits inside the tibia assembly, and 27T is the smallest the output pulley can go without the tibia length increasing too much.

The GIM4305 has a continuous torque rating of 1Nm and a peak torque rating of 3Nm; from the calculations it looks like we need ~2Nm of continuous torque, this is achievable, but I don't plan of having any type of cooling in the robot. Fortunately, there is a bigger brother in the same family (GIM4310), which claims to be able to do 3Nm continuous and peak 5Nm. As the name states, the only difference is the brushless motor is a 4310 instead of a 4305. There is one big drawback though, the rated speed drops significantly to 120 rpm compared to the 300 rpm of the GIM4305. This shouldn't pose an issue for walking, but I definitely want to robot to be able to jump. I calculated the angular speed of the knee motor for the jumping leg to be ~260rpm (27 rads/s), considering the 1:1.33 reduction at the knee (with the belt drive), the knee joint has to move ~190rpm (20 rads/s). If I change the ratio at knee to something close to 1:1, or maybe even multiplication, there should be nice balance between continuous torque and speed. Another downside of the GIM4310 is that it has 40% more mass than the GIM4305 and the phase resistance is closer to 2Ω.

Unsurprisingly, I decided to design a new Quadruped Robot based around the GIM4305. I am giving myself exactly 6 weeks to finish the design, manufacture and assemble the whole robot just in time for the 2023 Bay Area Robot Block party, which will take place this April 8th. Success will mean showcasing the robot at the event, walk around greeting participants and, if I'm lucky, interact with Boston Dynamic's Spot. There as some items from the development of DAGR that I will be leveraging to finish the challenge on time:

1. I have the last 12 Dagor Brushless Controllers (Alpha version) from before the semi-conductor shortage. Originally intended as my personal backup stash for DAGR and other personal projects, I am thrilled to employ them for this challenge. 

2. I have already figured out a good way to mount my motor controllers to the back of the actuators with a 3D printed plate. 

3. The femur and knee mechanism is already designed, though I believe I'm going to be making some minor tweaks here and there.

4. I intend to utilize the same tried-and-tested open-loop Kinematics model and gait generation stack that DAGR presently employs. The day I finish assembling the robot should be the same day it takes its first steps.

 I built a tiny test stand to do some torque measurements and quick bring-up. Using one of my Dagor Brushless Controllers and SimpleFOC I was able to start doing some motions after a bit of parameter tuning. The somewhat questionable datasheet seems accurate and measured peak torque was of 3Nm. Overall I'm very happy with the actuator, though there are a few caveats.

Positive observations:

• Different bolt patterns in the back which gave me flexibility when designing a plate to attach the Dagor Controller.

• Finish and machining were better than expected.

• Affordable price.

• Torque density for the price and form factor is great for projects where a quasi-direct drive solution is needed.

• I like the 3x M3 bolt patter and locating features in the output.

• It's very easy to attach a diametrically polarized magnet with a tiny 3D printer adapter on the back of the unit for the position sensor of my motor controllers.

Negative observations:

• The single strand enamel wire is thin and easy to break. Fixing a broken wire right where the wires output the body was very challenging.

• Not a fan of the three very small M2.5 bolt system that holds everything together, though I cannot come up with a better way to do this without altering the mass and form factor. Maybe using 5-6 bolts would provide better force distribution.

• I have my doubts about the longevity of the 12T input gear,