Robogames 2025 Build

[mikeferguson]

Preliminaries

• [x] Select motors and motor driver/controller
• [x] Design updated power and motion board (PMB)
  • [x] STM32 w/ Ethernet (use ST dev board?)
  • [x] Dual motor driver with encoders
  • [x] Hot swap for shore power (or 12v SLA/LiFEPO4 charger?)
• [ ] Design run stop switch
• [x] Design 4WD platform around new motors, use existing brain box

Software

• [ ] ROS 2 drivers for PMB
• [ ] Cone finding routine
• [ ] Stuck detector and recovery behaviors
• [ ] Negative drop detection

Continuation of https://github.com/mikeferguson/robomagellan/issues/9

[mikeferguson]

Potential components

• 37mm 50:1 gearbox claims 100RPM @ 100kg.mm (0.98Nm)
• 37mm 30:1 gearbox claims 150RPM @ 80kg.mm (0.784Nm)
• 42mm 24:1 gearbox claims 240RPM @ 95kg.mm (0.882Nm)

Motor Ground Speed Calculations

• 50:1 with 120mm wheels = 0.63m/s top speed
• 30:1 with 120mm wheels = 0.94m/s top speed
• 24:1 with 120mm wheels = 1.5m/s top speed
• 50:1 with 170mm wheels = 0.89m/s top speed
• 30:1 with 170mm wheels = 1.33m/s top speed
• 24:1 with 170mm wheels = 2.14m/s top speed

Torque Requirement

Estimating robot to weigh about 5kg, the RobotShop calculator estimates needing ~3Nm for the 170mm wheel, and ~2Nm for the 120mm wheel to go up a 45 degree incline

[mikeferguson]

Notes on Robot Weight:

• 4x Drive Motors = 205g each
• Battery Pack = 1.87lbs (4.114 kg)
• Livox MID360 = ??
• NUC - 470g
• Current Tub Mockup = 227g printed

Modeling TODO:

• [x] Tub: add mount points for covers
• [x] Tub: add mount point for camera
• [x] Tub: add charge port
• [x] Tub: add power switch
• [x] Battery Cover: add bottom stiffening ribs
• [x] Mainboard Tray: add stiffening ribs
• [x] NUC Tray: add stiffening ribs on sides
• [x] NUC Tray: add mount holes for NUC
• [x] NUC Tray: trim to clear battery connector
• [x] Top Cover: add Livox mount
• [x] Top Cover: add fender mounts
• [x] Top Cover: model fan hatch
• [x] Top Cover: add GPS mount points
• [x] Top Cover: add split and overlapping seam
• [x] Top Cover: add mount points to tub

Wiring TODO:

• [x] Ethernet: Livox to switch
• [x] Ethernet: NUC to switch
• [x] Ethernet: Mainboard to switch
• [x] Ethernet: AP to switch
• [x] USB: GPS to NUC
• [ ] USB: OAK-1 Lite Camera to NUC
• [x] USB: IMU to NUC
• [x] USB: AP to NUC (power only)
• [ ] Power: Mainboard to NUC (19V)
• [x] Power: Mainboard to Switch (5V - inline regulator on 12v rail?)
• [x] Power: Mainboard to Livox (12V)
• [x] Power: Battery to Mainboard
• [ ] Power: Battery to Charge Port

[mikeferguson]

Revisions done for second printing:

• Added 25mm to the width of the battery bay - network switch new resides in battery bay
• Added 2 more screws to hold battery bay cover on (6 total instead of 4)
• Countersunk the holes for the battery bay cover screws
• Increased the motor center hole from 12->12.5 mm
• Updated NUC tray with additional supports and stiffness
• Widened mainboard tray 9mm. Removed the non-symmetric aspects. Nearly backwards compatible (just needs to be trimmed 1mm on the side for network switch clearance)
• Added wire retention features to base tub to make it easier to install mainboard tray
• Added livox cable mount on left side cover

Print Settings:

• Tub - Support, Tree Style, 20 Degrees. 3 Wall loops, 20% infill Cubic Pattern
• Fenders - 4 Wall Loops (basically ends up solid)
• Battery Cover - 35% Infill
• NUC Tray - 25% infill
• Right Side Cover - Support, Tree Style. 3 Wall Loops, 1mm bottom shell

Known issues:

• Removed the flat sides of the livox cable hole since orientation is important for right angle cable. Might want to re-add later on
• Had to cut the wire retention part in the left rear of robot - it interferes with the Livox cable mount
• Cannot remove right skin without loosening left side skin because of the GPS mount. This might be fixable by adding a 6-8mm spacer under the GPS mount and using a longer 1/4-20 screw?

6/25/2024 - fully assembled robot weighs 8.5lbs without battery. The PS-1270 weighs 4.7lbs but a 12V 7Ah LIFEPO4 is only 1.8lbs