Finding a motor for the Arm Twister

Torque/Force - I found the amount of tangential force needed on the arm band by pulling on the velcro with a spring scale; 2 N provides a medium amount of twist, whereas about 5 N is the maximum amount of twist (couldn't pull it any more and it kinda started hurting).

Hobby motors - Looked for small, lightweight motors with enough torque. Not sure if we want them to be made out of plastic or metal; plastic is lighter but metal is more robust. Typically run the price range of $5 - $20.

* http://www.hobbyengineering.com/SectionM.html

• H01209-01Z Gear Motor 3: Right Angle Shaft $5.50
  65mm (2.56") long x 22mm (0.867") x 18.5mm (0.73")
  This motor offers 50 in*oz of torque, rotating 360 degrees every 1.6 seconds (38 rpm - just a hair slower than a servo), at 5V, drawing 600mA at stall (free running at 52mA).
• H01415-01C Gear Motor 9: Right Angle Shaft $5.50
  70.5mm (2.78") x 27mm (1.06") x 23mm (0.906")
  This 143:1 gearmotor is much like the GM3 gearmotor but runs at nearly twice the speed. This motor goes 66RPM at 5V, drawing 670mA at stall while providing 43 in*oz torque. Free running at 5 volts is 73.2mA.
• H01212-01D Miniature Gear Motor: Right Angle Shaft $5.25
  53mm x 13mm x 19mm (2.09" x 0.51" x 0.75"), and weigh in at only 20 grams (0.7oz).
  This gearmotor starts rotation at 0.58 volts, turning 7RPM drawing only 46.5mA. At 5 volts, this unit really humms, spinning at 145RPM and drawing 88mA no-load (610mA stall producing 20in*oz torque).
• H02532-01D Miniature Metal Gear Motor - 71 RPM $19.99
  1.14" (29mm) by 0.47" (12mm) by 0.39" (10mm) motor
  The motor has a free running speed of 71 RPM at 6VDC while drawing 50ma. It has a stall torque of 30.7 in-oz at 6v DC while drawing 533ma.

-- MelodyWu? - 09 May 2007

* Faulhaber motor

• found one lying around in the lab - 1724E006SR
  • e_1724SR_DFF.pdf: Faulhaber 1724E006SR motor specs
• using it for prototype testing
• called MicroMo? today and found out price -- $105 for motor + encoder (with academic discount)

-- MelodyWu? - 11 May 2007