The head of BB8 floats across the body on bearings. It’s held to the body by strong magnets that coorespond to other magnets on the inside of the sphere. Those inner magnets are affixed atop a mast that projects from the center of the vector bot. By rotating the shaft, you rotate the head.
This poses a few neat mechanical problems to address:
- It needs to attach to the center of the vector bot
- It must rotate freely
- It should be driven by a motor
- Need to be able to track it’s rotation
- Needs to fit through the 5.25″ opening in the sphere
The yellowish blocks represent the center of the vector bot. It’s important that this shaft be very close to the exact center so it always points to the outside of the sphere at the correct angle.
This is the finished version after 3D printing the necessary prices.
I have the code for this motor working. I need to refine it to make it smoother. There complications when programming bothe stepper motors and regular dc motors on the same controller. I’ll get into those in a later post once I solve the issues I’m experiencing.
Affixing anything to anything in such a way that it can be removed and repaired is a process that takes forethought.
With my early decision to implement a vector bot as the “shiftable weight”, it was imperative to find a way to attach panels to the outside of the sphere without inhibiting the wheels.
So, glue, right? Epoxy? I want these panels to be removable so I can make inevitable repairs and upgrades.
Bolting through the inner sphere was out. I can’t use magnets since the large magnet would just rip panels off with the dome.
I decided to use t-nuts. I would need to print spacers to make up the 3/16 or so difference between the panel circumference and the sphere circumference. I want to keep that gap for wires when I hook up the shell LEDs.
The spacers allow me to glue the t-nuts to the body without piercing the inner sphere.
It took me a few tries to get the spacer thickness just right. I settled on 2.6mm.
One of the panels can just be removed to access the inner vector bot. The others may need to be removed to get enough visability to assemble the bot in the sphere.
After the recent setbacks with stepper motors, I decided to focus on optimizing the two simplest forces at play: friction and torque.
The amount of friction increases when weight is added. After adding a few pounds of weights to my vector bot, the added friction on my axels was too much for my motor torque to overcome. The best way to reduce friction in my case was to add bearings.
This loss in friction allowed me to find motors that could supply enough torque in my price range.
After purchasing new motors and motor controls, I set about designing and 3D printing the new robot frame.
I also heat pressed t-nuts into the frame so I could use hex screws to secure the platform.
This is the robot upside down. After figuring out how to mount the weights and the battery, it was time to put the robot in the sphere.
More on the shell later and how I’m mounting it.
Vector bot in the sphere: