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The Speed Controller needs sensors to measure drive motor speed and steering rotation angle. For for dust reasons, open-frame optical encoders are probably not the best.

Drive Motor

For the drive motor, velocity is important, but absolute position is not.

  • This points to a low resolution, sealed optical encoder. Some options are here-

Digikey Encoders

  • Another possibility is a variable reluctance sensor. Here are some examples:

Geartooth Sensors

More geartooth sensors: http://www.allegromicro.com/en/Products/Categories/Sensors/ats.asp

these are very tolerant of dirt, but knowing direction costs money. two geartooth sensors, arranged an odd number of half-sprockets apart, could theoretically sense quadrature and thus direction. But we tried these, but they just didn't have the resolution to get good speed estimates. Otherwise they are great!

We finally decided on sealed optical encoders. These are the ones we used:

US Digital S5S-500-NT Softpot Optical Shaft Encoder, Sleeve bushing version with no added torque. 500 CPR http://www.usdigital.com/products/s5/index.shtml

Cabling: though the US Digital has mating cables available: http://www.usdigital.com/products/connect/5pin-finger-latching.shtml

It's likely easier to use ribbon cable with a six-pin IDC header (Digikey 609-2841-ND) to connect to the six-pin header on the daughterboard. To mate with the shaft encoder, use a .1 inch one-row female header like Digi-key part S7038-ND, and solder the other end of the ribbon cable

Steering Motor

For the steering motor, absolute position is important, and a fair degree of precision at the joint is desired. We used a sealed potentiometer.

The original steering pots were purchased from HDB Electronics in Redwood City. It appears that Jameco sells a similar part:


The Jameco unit may not be sealed. Should verify this.

Data on the steering pot (in case one or both suppliers stop carrying the part)

  • Actuator Orientation HORIZONTAL
  • Shaft Length .875"
  • Taper LINEAR
  • Tolerance +/-10%
  • Watts 2
  • Actuator Type SHAFT
  • Ganging Number 1
  • Variable Resistor Type POTENTIOMETER
  • Number of Turns 1
  • Resistive Element Material CONDUCTIVE PLASTIC
  • Body Dia. 1.09"
  • Resistance (Ohms) 5K
  • Shaft Dia. .250"