My team is currently using 393 motor encoders on their robot and they want to be able to extend the length of 4 wire cables used for those motors with 3-wire extension cables. Is this possible, or do we need to obtain more 4-wire serial cables (because we have run out and it doesn’t seem like they are sold on the store)
You can’t really do what you describe.
While you could do it in a very jury-rigged way without cutting cables, it would be a bad idea, and it probably wouldn’t pass inspection. And signal quality would suffer, perhaps to the point of being unusable.
The part you need is sold on this page:
The item is near the bottom:
4-Wire Extension Cable 12" (4-pack)
276-1949
Price is $19.99
So here you go
https://vexforum.com/t/answered-r15a-extension-cables-used-for-different-wire-count/25716/1
Official QA saying you can use 2 2 wire cables to extend a 4 wire IME. Or 2 3 wire cables to extend IME ( maybe IME + 2 wire motor could be extended over 2 3 wire extension cables to not have useless cables but would be more confusing).
Obviously plugging everything in correctly on both ends is on you and all wires should be accessible for motor testing.
Ya the 4 wire extension only being 12 inches is really annoying and 2 2 wire extensions is just an easy solution. I would suggest for anyone using this trick to always have the end going into the cortex and going into the motor be a VEX 4 wire extension just so the tabs help you.