I am trying to design robotic joints for a SCARA arm, I am mainly missing information about the shaft and bearings components.
Design would be similar to MakerArm / Dobot M1 kickstarter projects.
So Z translation would be built using a ball screw, the others joint would be more "classic" (I want to avoid belt/pulley).
And so here are the multiple questions pending in my head:
Why do we have motors with cylindrical shaft and others with a D shaped one? Are there other shapes? How do you chose the appropriate one?
Can you confirm that I should avoid mounting parts directly on the motor shaft, and instead use a 2nd shaft? For the Z-axis, I believe the ball screw can be considered as the 2nd shaft.
Concerning that 2nd shaft (if needed) which formula or abacus can I use to determine shape/diameter and whether it is hollow (how much?) or not.
Looking at universal robots joints in this video, Inside a Universal Robots Axis, it seems they use a hollow shaft while it seems harder/longer and more expensive to manufacture, so there may be a reason? Is it related to inertia?
Should I use a coupler between the two shaft that will act as a fuse?
Because in the video linked before I don't see any couplers. Gearbox (harmonic drive in their case seems) to be the only part between motor and output shaft. If needed which coupler would you recommend (keeping backlash low), oldham or another ?
Finally about bearings
For the Z joint (ball screw based) am I right, when saying that mounting methods have been "standardized" by CNC industry and available choices are between the following 4 "patterns", with standard "supporting" parts that includes the bearing?
For the motor part of these linear actuator they seem to often use "basic" DC brushed (or brushless?) motors and I saw 2 different mounting designs, one where the motor is in line with the ball screw
The 2nd one where the motor is parallel with pulley/belt or gears to transmit torque
Is it only a matter of space available or is one design more efficient than the other?
For the other joints, how do I know how many bearings, their size/type (depends on load type?), how to mount them and where (I already guessed it goes between the motor shaft and the part to rotate).
Thanks for reading/answering (even hints would be appreciated).