2020-05-26 Meeting Minutes - General

Update & Action Items

Member	Update	Action Items
Andrew	Compiled potential heat sinks Started spreadsheet to investigate attaching hub motors to wheels	Finish spreadsheet Draft sketch for hub motor joint and encoder attachment
Alaina	Weight of motors and wheels (2020 vs 2019 & 4 vs 6 wheel) Estimate weight increase for rocker bogie based on all wheel options (motors and tires)	Weight of joints for 6-wheel design CAD chain attachment for science mechanism CAD based on Tony’s FBD
Asha	Science seal v1	Science seal v2 Drive train FBDs Science motors calcs
Ayesha	BLDC motor list started
Caleb	Start sourcing actuators for science module Complete sourcing. Find sponsors with Lance’s help Gimbal design Help with fin sourcing	Sourcing for Science module (get more specific requirements from Asha) Check with Lance about contacting sponsors Gimbal design - look into PCB placement
Cindy	Research IMU mounting considerations	More research on IMU transforms (check ROS), Research effects of high frequency signals on IMU Looking for KDL (or other) libraries for reference
James	Found Tripod on Bestbuy that can hold load and is within budget: LINK? Talked to Tony about this	Look for alternatives of similar form factor
Tony	6 Wheel FBD geometry calculations PM work with Drive Train	Implement 6 wheel FBD loading equations and compare 4 vs 6 wheel Wheel Hub research (details for Drive Train team on trello) Determine how to do tangential normal frame transforms for 3-D vectors, leave details to Cindy Understand BLDC better to determine if the ebike simulator is sufficient for emulating smaller motor torque - speed curves, and what kind of input parameters are required Order an Odrive and pick out a few motors that are within budget for testing
David	Completed shovel redesign CAD Science module design review	Prototype shovel Look into custom battery pack Finalize component list for e-box
Cole		GIMBAL
Emily	Began hub motor research	Continue hub motor research Refine science seal ideas with Asha

Blocking:

This person	Needs to finish this	For this person	To be able to do this
Tony	FBDs	Alaina	Drivetrain CAD
Asha	Science motor calcs	Caleb	Specing motors
Tony	Gimbal talk	Caleb	Gimbal work

General Notes

New member introductions
Spaenaur sponsorship
- Called spaenaur today, they are still onboard to do in-kind sponsorship for anything on their catalog, which is alot of stuff.
- In the interest of saving money, please take a look at catalog next time you are looking for OTS components, especially fasteners. LINK

Lightning talk - Screws and Bolts

Target audience: EGAD people
Difference between bolt and screw:

Bolt entails having a nut on one end; holding one end still while turning the other
Screw is just screwing in one object

When you screw in a bolt, the bolt is in tension and that causes the joints between to be in tension
Screws translate torque load into vertical force load

Tr - raising torque
F - axial load
dm - mean/pitch diameter
f - friction coefficient between bolt and thread
a - angle of thread
l - thread pitch

If screw head friction is non-negligible you need to account for the torque loss due to friction with the bolt head.

In this formula, u = fsecα
dc - mean collar diameter
uc - coefficient of friction for collar

This is important because

If bolts aren’t sufficiently tightened, they can loosen over time
If a bolted area undergoes a load greater than the tensile load due to the bolt, assembly geometry can change
Excessive bolt preload can cause fasteners and parts to deform

Want to keep bolt stress within 75-80% of the yield stress (called the proof load)
Bolt elongation: turn a bolt a quarter turn after you start to feel it get tight