This one is a bit dated, but the lessons are still relevant. [Zach Hoeken] posted about the challenges he faced building a CNC stepper driver. He was experimenting with Toshiba motor drivers back in 2012.
The modular motor driver boards he built were based on the THB6064AH – capable of 1/64th step, and 4.5 Amps at up to 50V. [Zach] built a test jig to run the boards through their paces. A couple of messed tracks was the least of his problems – easily fixed by cutting traces and using jumper wires to correct the errors. But the header footprints for the motor drive boards got reversed. The only way out was to solder the headers on the back side.
LESSON : Always check footprint orientation and pin numbering before sending boards to fab.
The surprising part was when someone as experienced as [Zach] messed up on Ohms Law. Based on the current he wanted the motors to run at, his sense resistors needed to be 3.2W, but he’d used SMD footprints (0805 likely) instead. Those tiny resistors couldn’t be used at all, and the 5W resistors plonked on looked like an ugly hack.
LESSON : Remember the basics. High current tracks, power components, high speed digital layout, shielding, heat sinking and the many other parameters to keep in mind while designing boards.
Finally, part number confusion proved to be his biggest challenge. THB6064AH is not the same as THB6064H. The difference is not a lot, but enough for him to suspect everything other than the chip itself. The good part was learning tons of stuff while probing and testing to get to the bottom of the issue.
LESSON : Please make sure your BoM lists exact part numbers used in your designs.
An example would be mixing up the ATmega328P vs the ATmega328 – the chips have different signatures, brownout, and power usage. Easy to fix, but this can cause some tense moments while trying to figure it out.
If you’re wondering where you’ve heard the name [Zach Hoeken] before, he was one of the founders of Makerbot.
Thanks [Peter Montgomery], who sent in this tip while he stumbled upon while searching for Toshiba stepper driver chips.
Fail of the Week is a Hackaday column which celebrates failure as a learning tool. Help keep the fun rolling by writing about your own failures and sending us a link to the story — or sending in links to fail write ups you find in your Internet travels.