TamiyaSixSpeedGearbox

ME112Notes

Pololu #74 Tamiya 72005 6-Speed Gearbox Kit

• ratios: 11.6, 29.8, 76.5, 196.7, 505.9, 1300.9

Motor = Mabuchi RE-260RA-2295 (data sheet) -- 2670

(another data sheet) -- 2670

• nominal no-load motor speed: 6300 rpm = 659.7 rad/sec
• nominal no-load current (mA) 160
• nominal stall current @1.5V 2560 mA
• nominal stall torque @1.5V 0.69 oz-in = 4.90e-3 Nm
• see datasheet above for nominal speed, current torque, at max efficiency

Metric gear module: http://www.metrication.com/engineering/gears.html

• Module = pitch_dia/N where pitch diameter is in mm, N = teeth
• As usual, addendum diameter = pitch diameter for N+2 teeth
• For the large blue gears in the gearbox, N=36
  • Measured with calipers: addendum diameter ~ 19mm, which would be the pitch diameter for a gear with N+2 teeth. So module = 19/38 = 1/2
• Face width = 3mm
• Material = nylon. Flexural yield stress ~ 60Mpa or perhaps somewhat less for endurance (see links below).

Encoder for testing the motor:

• http://androminarobot-english.blogspot.com/2017/03/encoder-and-arduinotutorial-about-ir.html
• Helps to put a capacitor across the sensor to reduce false spikes

Some useful links for nylon gears:

• http://www.substech.com/dokuwiki/doku.php?id=thermoplastic_polyamide_nylon_6 Nylon 6 properties
  • Flexural strength ~91MPa (130ksi)
• https://khkgears.net/new/gear_knowledge/gear_technical_reference/gear_materials.html
  • They suggest 62 N/mm^2 = 62MPa for injection molded gears. Other sources (e.g. Davis2005) suggest more like 45MPa so it may depend on the quality of nylon or it may be the latter is a safe endurance limit.
• http://sdp-si.com/plastic/design-of-plastic-gears.php - suggests 20deg pressure angle most common and has some simple adjustments for speed, temperature, etc.
  • refers to formulas in the Gear Durability section: http://www.sdp-si.com/resources/elements-of-metric-gear-technology/page10.php. (scroll down to Section 18.2)