📃 Adds more docs
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Rune Harlyk
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Spot is comprised of a 3D printed body, some hardware and list of electronic components.
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## Body
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## Hardware
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Spot is 3D printed and is a combination of different Spot Micro designs, with some minor modification on top.
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The original design is developed by KDY0523.
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* [robjk reinforced shoulder remix](https://www.thingiverse.com/thing:4937631)
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* [Kooba SpotMicroESP32 remix](https://www.thingiverse.com/thing:4559827)
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* [KDY0532 original design](https://www.thingiverse.com/thing:3445283)
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- [robjk reinforced shoulder remix](https://www.thingiverse.com/thing:4937631)
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- [Kooba SpotMicroESP32 remix](https://www.thingiverse.com/thing:4559827)
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- [KDY0532 original design](https://www.thingiverse.com/thing:3445283)
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The 3D prints is assembled with some additional component:
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* 84x M2x8 screws + M2 nuts
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* 92x M3x8 screws + M3 nuts
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* 64x M3x20 screws + M3 nuts
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* 12x 625ZZ ball bearings
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- 84x M2x8 screws + M2 nuts
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- 92x M3x8 screws + M3 nuts
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- 64x M3x20 screws + M3 nuts
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- 12x 625ZZ ball bearings
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## Electronics
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These are the electronics i used for mine and can easily be switched up to suit your Spot's needs.
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* ESP32 cam - Brain
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* OV2640 160° - Camera
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* PCA9685 - Servo board
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* 12x 20kg(or higher) servo motors
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* MPU6050 - Inertial measurement unit
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* GY-271 - Magnetometer
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* SZBK07 - 20A DC-DC Buck Converter
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* LM2596 or XL4015 - DC-DC Stepdown Module
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* 2x HC-SR04 - Ultrasonic Distance Sensor
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* 0.96" SD1306 - OLED diplay
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* ACS712 - Current sensor
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* ADS1115 - 16 bit analog to digital converter
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* Power button w/ led
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* 4x 18650 Li-ion battery in 2P2S configuration
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* Couple of resistors (10K, 47.7k, 33K)
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* 4x Servo extension cables
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| Component | Specification | Required | Recommendation |
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| ------------------------- | ----------------------------- | -------- | ------------------------------------------------------------------------------------------------------- |
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| ESP32 | Brain | Yes | ESP32-S3 (N8R8) with a camera. |
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| OV2640 or OV5640 | Camera | No | 120-160° |
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| PCA9685 | Servo board | Yes | Add thicker solder traces |
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| 12x Servo motors | Actuators | Yes | 20kg-35kg with high speed. If they are rated for your battery voltage you can skip the step down module |
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| MPU6050 | Inertial measuring unit (IMU) | No | GY-87 or MPU-9250 include magnetometer |
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| HMC5883 | Magnetometer | No | GY-87 or MPU-9250 include magnetometer |
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| Power switch | Main power switch | Yes | |
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| Power button w/ led | Mode switch controller | No | |
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| 2x HC-SR04 | Ultrasonic Distance Sensor | No | |
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| LM2596 or XL4015 | DC-DC Stepdown Module | Yes | Should be set a 5V for the ESP32 and peripherals |
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| 0.96" SD1306 | OLED display | No | |
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| SZBK07 | 20A DC-DC Buck Converter | No | Stepdown to servo voltage. If you select servos rated for you battery voltage, you don't need this. |
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| 7.6-8.4V Battery | Battery | No | Im using 4x 18650 in 2s2p configuration, but other people have 2s LiPos. |
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| 4x Servo extension cables | Servo extension cables | Yes | You can either buy them or make them with a couple or headers and some cable. |
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I recommend getting a ESP32-S3 with a camera, allowing for more computation and imaging capabilities.
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It means a more responsive robot as its faster doing sensor fusion, calculating kinematic and gait planning, and networking.
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# 🦾 Kinematics
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To enable complex movements, it's beneficial to be able to describe the robot state using a world reference frame, instead of using raw joint angles.
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The robot's body pose in the world reference frame is represented as
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$$T_{body}=\left[x_b,y_b,z_b,\phi, \theta,\psi\right]$$
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Where
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- $x_b, y_b, z_b$ are cartesian coordinates of the robot's body center.
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- $\phi, \theta,\psi$ are the roll, pitch and yaw angles, describing the body orientation.
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The feet positions in the world reference frame are:
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$$P_{feet}=\left\{(x_{f_i},y_{f_i},z_{f_i})|i=1,2,3,4\right\}$$
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where $x_{f_i}, y_{f_i}, z_{f_i}$ are cartesian coordinates for each foot $i$.
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Solving the inverse kinematics yields target angles for the actuators.
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<!-- Write about the calculation, rotation matrix and trig -->
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<!-- L1, L2, L3, L4, L, W -->
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<!-- $$
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R_{body} =
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\begin{bmatrix}
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\cos\psi\cos\theta & \cos\psi\sin\theta\sin\phi - \sin\psi\cos\phi & \cos\psi\sin\theta\cos\phi + \sin\psi\sin\phi \\
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\sin\psi\cos\theta & \sin\psi\sin\theta\sin\phi + \cos\psi\cos\phi & \sin\psi\sin\theta\cos\phi - \cos\psi\sin\phi \\
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-\sin\theta & \cos\theta\sin\phi & \cos\theta\cos\phi
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\end{bmatrix}
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$$ -->
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# 🏁 Motion state controller
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The motion controller is a finite state machine with state allowing for static and dynamic posing, 8-phase crawl and bezier bases trot gait, and choreographed animation.
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## Controller Input Mapping
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The controller input is interpret different between the modes. For the walking it it looks like this:
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| Controller Input | Mapped to Gait Step | Range |
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| ---------------- | ------------------- | ------- |
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| Left x joystick | Step x | -1 to 1 |
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| Left y joystick | Step z | -1 to 1 |
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| Right x joystick | Step angle | -1 to 1 |
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| Right y joystick | Body pitch angle | -1 to 1 |
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| Height slider | Body height | 0 to 1 |
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| Speed slider | Step velocity | 0 to 1 |
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| S1 slider | Step height | 0 to 1 |
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| Stop button | E stop command | 0 or 1 |
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<!-- ### Static and dynamic posing -->
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## Walking gait
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General about walking gait
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Time step
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Phase condition
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Stance and swing controller
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## 8-phase crawl gait
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The 8-phase crawl gait works by lifting one leg at a time while shifting its body weight away from the leg.
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As the name implies, the gait consist of 8 discrete phases, which represents which feet should be contact the ground or be in swing.
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At each time step the phase time $t\in [0,1]$ is updated. When $t\geq 1$ the phase index is updated and phase time is reset.
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Is derived from [mike4192 spotMicro](https://github.com/mike4192/spotMicro)
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## Trot gait (12 point bezier curve)
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The trot gait implements a phase time $t\in[0,1]$, but instead of using contact phases we define a swing/stance ratio of phase time offset for each leg.
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The stance controller implements a sin curve to control the depth of steps.
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The swing controller implements a bezier curve using 12 control points centered around the robot leg.
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Rotation is calulated using the same curve
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