Encoders

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!

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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:

http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&pa=13995&productId=13995

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"