Gen L Electronics
Release status: experimental
| Description | GenL Electronics is an in-development electronics package optimized for cost and software hackability
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| License | GPL v2
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Generation "L" electronics are a still unassembled 4-axis motor controller platform designed to be very easily assembled and relatively cheap. Total electronics cost (including opto-endstops and other off-board parts) is under $70 when ordered in 1-board quantities. It uses two circuit boards: one for power, one for logic. The boards can be manufactured in China for $3 and $2 respectively (lots of 10). Total part count is ~80 and all but 1 are through-hole for easy hand soldering.
The motors are controlled by Allegro A3992 stepper drivers via SPI. This controller is capable of 1/32-microstepping and the Teensy should be able to comfortably achieve full precision at speeds under ~4 inches/seconds. At higher speeds the resolution will gracefully degrade to 1/16th-microstepping.
The latest development code is available at: https://github.com/loganb/GenL
Software
Software for the board is as-yet, unwritten. The goal is to use the Teensy to do only the minimal work necessary to drive the controllers and read the sensors, leaving complex, floating-point math to the done on a host computer. The Teensy has a full-speed USB interface built-in for easy programming and interfacing. Stepping commands will be issued at a fixed rate, regardless of stepping rate, so at motor velocity increases, precision will gracefully decrease. 1/32 microstepping will be supported up to ~3.5 inches/sec.
Hardware
GenL consists of two circuit boards: a controller board and a driver board. The driver board is based around the Allegro A3992 driver. It supports 1.5A motor currents, 8-50V supply voltages, and 1/32 microstepping. The A3992 interfaces with a microcontroller via SPI. The companion controller board is connected to the driver board via a 20-pin ribbon cable that, in addition to carrying logic power and SPI lines, also exposes the VRef current limit pin on each controller to the microcontroller. This allows the microcontroller to vary the current limit in software and independently for each driver.
The controller board is designed around the Teensy 2.0 microcontroller. Unlike other designs, this one requires the uC to do more work since each motor driver must be stepped by sending 24-bits over the SPI line. In exchange for this additional overhead, the reduced pin-count frees up enough pins for software-controlled current limiting.
The total BOM for this design is approximately $70 per board set, making it the cheapest currently available. WIth 32x stepping, it is also the most precise, though other designs support a somewhat higher driver current (2A vs 1.5A). The ground traces are specially shaped to maximize heat dissipation and the drivers may be able to sustain higher currents than designs without driver heat sinks.
Obtaining
All designs and the BOM are available on Github. Unassembled kits are now available for purchase for $75 + shipping (see http://genl.posterous.com/introducing-gen-l).
