Experiments with Stepper Motors

Deal Extreme has a large number of electronic modules for very low prices and, in most cases, shipping is free. Among these modules is the break out board for an A4988 Stepper Motor Controller. This tiny device can switch up to 2A at 35v, according it its data sheet.

From other sources (inoperable photocopiers) I have several stepper motors. My initial experiment is to see whether I can mount two of these motors back to back, stick some wheels on them and make a small, steerable robot. This has been done many times and the Internet is full of write ups and how tos so it shouldn't be too difficult to achieve.

Step 1 - Stepper Motor Assessment
The model I have is a 14PM-M247. This is a hybrid stepper motor, performing 1.8 degrees per step and rated at 24v. The product page lists 2 versions of this model. One is uni-polar and other is bi-polar. My motor doesn't specify which one it is.

Unipolar vs Bipolar are quite different motors, needing different signal patterns to drive the motor. It turns out that 6 pin motors (such as this one) are universal, or can be used in either a unipolar or bipolar mode.

While the motor has 6 pins, the plug it came with has only 4 wires.The two common pins (2 and 5) are missing. This means it was being used in a bipolar mode.

Pin numbers start at the right hand side, when looking down on the motor with the shaft up. 1 and 3 are the B coil and 4 and 6 are the A coil (A -> B is left to right and 1 -> 6 is right to left...confused?)

Step 2 - Driver Assessment
The driver has two electrical sides to it. A low voltage (logic level) side of 3 - 5.5v and high voltage side (motor level) of 8 to 35.

In the minimal configuration one logic level connection, to signal when to step, is all that is needed on the low side and 4 connections to the motor on the high side. It should be noted that the direction pin should be connected to ground or power, if not connected to a logic pin, otherwise results will be unpredictable.

The drive also supports microstepping, which allows a greater degree of control, although accuracy may suffer. I'm not interested in microstepping at this point so I'll ignore these inputs.

Current limiting is an important aspect that is well covered in this video. The basic message is to not skip the step of adjusting the current limiter to match the motor.


Summary

Feature	Motor	Driver	Compatible?
Voltage	24v	8v - 35v	Yes
Current	0.8A	2A	Yes
Style	Universal	Bipolar	Yes

Overall, it seems that these devices should work together. We'll see...

Fooling Around in Arthur's Pass

It’s always the same. The size of the peak, the effort spent getting there or whether it’s on the ‘must climb’ peaks list doesn’t diminish the need to holler and dance a little jig, basically behave like a damn fool, when topping out or “running out of earth”.

I always prefer the most direct route (for the last few metres anyway). A short section of vertical is a good excuse to load the front points and pop onto the top, after enjoying a brief Kilroy moment.

Mt Damfool is no different. Many people say, with a wry smile, “you’d have to be a damn fool to climb it” but I prefer to think whoever named it was speaking in the positive, not the negative.

The peak stands at 2030m, above Fools Col, to the north of an easily navigable bowl at the head of the Anti Crow River.

Looking E, down Anti Crow Valley

The Anti Crow Hut is accessed, when the Waimakariri River is low, from the car park opposite Klondike Corner, in about an hour and a half. When we arrived, at around 2230 Friday night, it was full as is often the case. 

Bivvying outside is a good way to get an “early” start so by 0700 the next morning we were making our way SW, up the Anti Crow River.

The most arduous section of the trip is climbing the scree slope on the true right of the Anti Crow River to gain the top of the roughly 20 metre waterfall. A quick stop for a boil up and one of those soups that always tastes amazing in the mountains and terrible at home, then onwards up the snow slope to the top.

Looking W, up Anti Crow Valley

By 1400 the weather had clagged in, with just the occasional patch of blue, but the half hour fooling around on the summit was rewarded with snatches of views in all directions.

The original plan was to head out via the Mottram Peaks, and maybe biv at the bush line, but with rain threatening the hut had more appeal. Unfortunately, upon arriving at the hut, we discovered it was, once again, full, but this time of hunters and enough beer to sink a rather large battleship. Apparently, if you ask the right person, you can obtain permission to drive quad bikes up the river into the park. I guess the beer must have been Tui (yeah right!).

Unwilling to spend the night out in the rain or ford the Waimakariri River in the dark we opted to use the track and head over Turkey Flat to the road, finally arriving at the car at 0030. An 18 hour day wasn’t quite what we’d planned but, in the words of Charlie Chaplin, “It takes courage to make a fool of yourself”.