OK, maybe not as dramatic, but it was just as vital.
With my final project deadline extended a week, I took a couple days of downtime to catch up on sleep. The all-nighters were adding up. Now I’m back and making some minor changes and a few fixes. Hopefully the thing will drive in reverse without catching on fire. If you don’t hear from me, send help.
Firmware for the not has been fleshed out and I’m looking forward to getting it coded. The loop is simple, checking the status of each input and setting a flag. That flag is passed to the three output functions, which run after the input stage. One exception is the turnaround() function, which is called by an interrupt on the whisker pin. Some output functions call themselves to complete a series of drive commands, for instance. This keeps things simple.
More to come.
Mounting at the rear, near the motors, his board is centered around a SN754410, a quad half bridge driver. The IC includes clamping diodes, but external Schottky diodes add an extra layer of protection from potentially ruinous flyback current.
Fresh from the journey from ShenZhen (via Thailand), these NEMA 17 motors have a rotation of 3.75 degrees and a phase resistance of 6.4 ohms. They are rated 5VDC at 0.5A, and are manufactured by the Minebea Motor Manufacturing Corp. The cost was under $10 each on eBay, with free (3 week) shipping.
Unfortunately the leads included have an incorrect connector, but I managed to carefully force one in order to test. As this places significant strain on the motor connector, it is not advisable to operate these motors long-term with the incorrect connector. Here are some photos.
Solid motor with incorrect connector. Notice the notches on the motor connector that do not match the supplied connector.
Significant strain is placed on the connector due to the mismatch.
While OK for testing, operating a motor with the incorrect connector will lead to premature failure.
I await a response from the eBay merchant as to how they will correct this problem. Stay tuned!
Exciting progress! Stay tuned for more…