Motor info
To keep the cost down, this design uses the widely available 28byj-48 geared stepper motors. These are super cheap and easy to find, and also don't require an expensive stepper motor driver! The unipolar design and low current draw mean they can be driven by a simple ULN2003 darlington array.
However, there are actually a number of different motor configurations that all go by the exact same "28byj-48" model number! Graham Wideman has posted a bunch of detailed notes on these motors which are worth a read, and my own notes are below.
I originally used the most common 5V variety, but later switched to a 12V version which seems to have better torque.
| Model | Voltage | Steps/Rev | Measured Coil Resistance | Source |
|---|---|---|---|---|
| 28byj-48 | 5V | 2037.8864 | 27Ω | AliExpress |
| 28byj-48 | 12V | 2048 | 71Ω | AliExpress |
(When ordering parts, please see the Ordering Splitflap document for the most up-to-date recommended sources)
The difference in internal gear ratio was particularly surprising to me, but after doing a number of full-revolution tests I'm fairly certain that the difference is accurate. It's also worth noting that although the product photo for the 12V model showed a different, 4-hole mounting bracket, the motors I actually received had the normal 2-hole mounting bracket. I'm not sure whether this discrepancy is typical.
