CartMightyStep17 A4982 Stepper Driver - MAKERBOT-MIGHTYSTEP17
Released: October 2016
Need to replace a burnt-out or dead MakerBot BotStep17 stepper driver? This is a fully compatible re-designed stepper driver for the MakerBot Replicator 1 and Replicator 2/2X. These are made to drive any stepper motor (like NEMA17 type motors), in either full, half, quarter, or sixteenth micro-step resolution. The foot print is similar to other A4988, DRV8834, or DRV8825 based boards.
The MightStep17 driver is based on the original A4982 stepper motor driver chipset which used on the MakerBot and is current limit programmable from the MakerBot MakerWare application. It uses the same 0.270 Ohm sensing resistor to make the current scale the same. These drivers are hard to come by after 2015, when MakerBot Industries stopped making them.
Thermal design has been improved to make it run cooler and easier to attach heatsink. All the components follow MakerBot specifications or better to make this a reliable drop-in replacement - no need to tune hard-to-get-to potentiometers or other tweaks like on similar boards.
The Vref voltage is found using the formula: Vref = Imax x 8 x Rsense, where Imax = max. driving current (per coil), Rsense is the sensing resistor value (0.27 Ohm on this board). It can handle up to 1A as it is and 2A with cooling (fins, fans, etc.) But it is limited to 772mA, see below.
MakerBot MightBoard has a digital potentiometer on the lower-end of a 5V voltage divider, allowing adjustment of the Vref for the stepper driver. The Vref voltage ranges from 0 when N=0 (set in MakerWare device prefs) up to 5V x 5k/(5k+10k) = 1.667V when N=127. The stock settings are 118 for the x, y, a, b steppers and 50 for the z-axis. This results in Vref = 5V x (5k x 118/127)/((5k x 118/127)+10k) = 1.586V and driving current of Imax = 1.586V/8 x 0.27Ohm = 0.736A (736mA). The max. driving current you can get with this board on a MakerBot is Imax = 1.586V/8 x 0.27Ohm = 0.772A (772mA).
Update: After February 2017, the Rsense is changed from 0.27 Ohm to 0.20 Ohm to provide an improved upper-end of the driving current range. This allows you to configure 1A driving current (N=127 in MakerWare) on the MakerBot Replicator 1 and 2X (up from 0.772A). The added torque makes it easier to drive tight extruder feed devices with high-compression springs and ball-bearings that would otherwise keep the stepper motor click-click. This means that the scale-factor in MakerWave device preferences has to be lowered 20%, or from the default 118 to 95 for x, y, a and b driver, to keep the same driving current. But you can also leave it as it is to get a more robust operation, at the expense of higher torque, heat and noise.
| MS1 pin | MS2 pin | Microstep resolution | Excitation mode |
| L | L | Full step | 2 phase |
| H | L | Half step | 1-2 phase |
| L | H | Quarter step | W1-2 phase |
| H | H | Sixteenth step (MakerBot) | 4W1-2 phase |
Features
- Fully re-designed stepper driver for MakerBot Replicator 1, 2 and 2X
- Based on original Allegro A4982 chipset
- Drop-in, BotStep17 compatible, stepper motor driver
- Handles any stepper motor up to 1A load without heatsink
- 6 to 35V motor voltage range
- Assembled and thoroughly tested in Europe
Specifications
- Product ID: MIGHTYSTEP17
- Type: Microstepping driver board
- Logic voltage: 5V
- Motor voltage: 35V max.
- Current rating: 2A max. per coil
- Current sensing resistor: 0.200 Ohm (0.270 Ohm before February 2017)
- Working temperature: 150°C max.
- Current setting: digital or potentiometer voltage adjustment
- Pin spacing: 2.54mm
- Weight: 12 grams
- Contents: 1x MightyStep17 board, 2x 8-pin headers