Project Hexapod Part 2: More walking design thinking

Each leg on this robot has 3 motors; a shoulder, an elbow, and an ankle

To make things easier I labelled them up like this:

There are 18 separate motors to control:

			Board	Servo				Board	Servo
Left	Front	Shoulder	Pwm1	8	Right	Front	Shoulder	Pwm1	7
Left	Front	Elbow	Pwm1	10	Right	Front	Elbow	Pwm1	5
Left	Front	Ankle	Pwm1	13	Right	Front	Ankle	Pwm1	2

Left	Middle	Shoulder	Pwm1	9	Right	Middle	Shoulder	13	6
Left	Middle	Elbow	Pwm1	14	Right	Middle	Elbow	14	1
Left	Middle	Ankle	Pwm1	15	Right	Middle	Ankle	15	0

Left	Back	Shoulder	Pwm2	8	Right	Back	Shoulder	Pwm2	7
Left	Back	Elbow	Pwm2	9	Right	Back	Elbow	Pwm2	6
Left	Back	Ankle	Pwm2	10	Right	Back	Ankle	Pwm2	5

Design Thoughts

First thought was to create a function that controls each limb. At the least every limb should move in the same way. However, whilst limbs move together from the gait perspective (Figure 2) I don’t think we can do that from an Arduino perspective. I don’t think I can create a function that says move limbs L1, R2, L3 at the same time. I think I’ll need a function that does that. But then separately what it’s doing is moving “Left Front Shoulder, Right Middle Shoulder, Left Back Shoulder” together, then “Left Front Elbow, Right Middle Elbow, Left Back Elbow”, etc. until that function is complete.

I think I’ll have a multidimensional array with degrees in it for each joint. What I might do though is write a routine which sets each joint to 0. Then unscrew and reattach the joints so I know where zero is on each motor. Either way, I probably need a few lists to define:

the start and end position of each joint for a forward motion

the start and end position of each joint for a circular motion

the start and end position of each joint for being sat still.

That currently looks like this:

Name	Board	Servo	servo_min	servo_max
LeftFrontShoulder	Pwm1	8	500	500
LeftFrontElbow	Pwm1	10
LeftFrontAnkle	Pwm1	13
LeftMiddleShoulder	Pwm1	9
LeftMiddleElbow	Pwm1	14
LeftMiddleAnkle	Pwm1	15
LeftBackShoulder	Pwm2	8
LeftBackElbow	Pwm2	9
LeftBackAnkle	Pwm2	10
RightFrontShoulder	Pwm1	7
RightFrontElbow	Pwm1	5
RightFrontAnkle	Pwm1	2
RightMiddleShoulder	13	6
RightMiddleElbow	14	1
RightMiddleAnkle	15	0
RightBackShoulder	Pwm2	7
RightBackElbow	Pwm2	6
RightBackAnkle	Pwm2	5

Maybe a piece of code that takes serial input and resets the device to zero’s.

Control System:

Due to its built in Bluetooth, I’m thinking about having a raspberry pi zero-w connected to an Arduino nano over USB Serial:

https://maker.pro/raspberry-pi/tutorial/how-to-connect-and-interface-raspberry-pi-with-arduino

ser=serial.Serial(“dev/ttyACM0”,9600)

Then I can both ssh into the robot to tell it what to do. And I can also write a phone app to act like a remote control, connecting over Bluetooth. The v5 of the robot car did that.