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Meeting Minutes - Conversation with Theo Camilleri from the FSAE team
- Rules of thumb
- Think of how you (or someone with little manufacturing experience) would manufacture a part. This helps with choosing good tolerances
- Document your entire design process
- Tolerances are incredibly important
- Problematic things
- Getting sponsor parts made - takes a long time. Manufacture on a reasonable time scale
- Making sure gears are easily manufacturable; DFM is critical
- Rack housing needs to have concentric holes
- Critical tolerances on gear meshing
- Ackermann Steering
- Figure out way to vary Ackermann settings; i.e moving it forward and backwards. Make position customizable because testing actual physical components is a great way to validate the system
- Look at skid pad and accelerometer to determine lateral scrub
- Bump steer
- They use Adam’s Car, a software for vehicle dynamics simulation. The hardest part is setting the car up, but past that it’s fairly straightforward
- Their car was already set up a while ago in Adam’s Car
- Goal; just minimize bump steer as much as possible; the FSAE team doesn’t have an exact number target
- Google bump steer testing and perform tests in real life; try locking out steering wheel, put a plate on the wheel, and figure out how much the plate turns when the tire is moved up and down
- They currently have 0.3° under max travel
- Bump steer is based on tie rods, i.e. it’s independent of rack position
- The FSAE team is almost never at full lock
- The FSAE team’s process for rack design
- Start with load cases
- Get driver input loads
- Validate loads with strain gauges on an existing system
- Look at other steering systems and their solutions
- Look at FSAE-specific racks
- The FSAE team’s rack and pinion design/manufacturing
- Spur gear is used for pinion; they’ve been doing this since 2013
- Designing for manufacturability is extremely important
- They use mostly 4140 and 4140 steel (steel that hardens well) for gears
- Gears get treated to 40-44 Rockwell C (Rockwell is a hardness scale for metals, and C specifically pertains to hard steels)
- They use 6061-Aluminum for the rack
- Aluminum parts are anodized for aesthetics
- Manufacturing company probably just hobs the gear
- Difficult to get sponsors to do helical and double herringbone gears
- Both rack and pinion are equally critical to get tolerances right for
- pinion was designed to last for 2 or 3 years; figure out how many comps it should be able to go through
- Other steering component design and manufacturing
- Determine car’s life and design less critical parts/ parts that can be maintained easily based on that period of time
- Rack Housing
- Concentricity of holes is critical for having a good rack and pinion
- They made it from separate pieces and used adhesives to bond parts together
- Steering column
- top of column is held together with a crossbolt
- no team really does belt drives
- Comments on manufacturing in general
- Tolerances are incredibly important; FSAE has standards for some areas
- The rack and pinion require tight tolerances
- Rack housing requires tolerancing for concentricity of holes
- Specific to the FSAE team - low tolerance: +/- 0.25mm, high tolerance: +/- 0.1mm. Anything higher is unattainable for manual machinists
- High tolerance places: concentric holes for housing, diameter of steering rack
- Set a target for how much compliance you want (they have 7º of backlash)
- Mechanical issues
- linkage failure is large problem at comp
- Quick release on steering wheel had biggest source of backlash
- Maintenance
- Buy new u joints every year
- Don’t bring u joints past max angle
- Grease rack every month
Other forms of steering
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