Combining V5 and 393 motors - should this be allowed?


As I understand it, the V5 brain will be able to support up to about 8 of the 393 motors via some 3-wire ports. Also, I think the game manual specifies only 4 options for motor and pneumatic combinations, all 4 of which specify that a team can use either all V5 motors or all 393 motors but not a blend of the two motor types.

Since Vex isn’t getting the V5 motors shipped out until the end of this month (maybe? chuckle chuckle), I was thinking that another motor combination option should allow for the blended use of 393 motors and V5 motors so long as the 393 motors count as V5 motors. In other words, since the number of all-V5 motors would be limited to 8, a team could use a combination of V5 and 393 motors so long as the total number of motors would not exceed 8. My reasoning is that the students could make the transition to V5 without necessarily having a major upset to ALL of their subsystem designs. Otherwise, it will make the transition to V5 look even more risky, even more irritating than it already will be in the middle of the season, etc.

Does this suggestion seem reasonable or is there something I am overlooking? Has somebody already gone over this?

Darn it, I can’t even access the official Q&A anymore because of the changes made on the forum.


the motors only run at 5 volts


As above, 393s would be almost useless on a competition robot via the V5 Brain.
There is no reason that for testing and development, you couldn’t use them, but not on subsystems that need any grunt.


We converted an old NbN robot to V5 for beta testing with 2x 393 and 4x V5 motors. Only the intake and ball advance motors were 393 with a fairly light average load. As noted by others the 3 wire ports are 5V only but also limited to a maximum total current of 2A. Going from zero to full power on both motors simultaneously caused the 3 wire port group over current sensing to trip (latest beta firmware release).

To make 393 motor usage viable on the V5 platform, beyond very light duty, an external smart port expander module is needed. This has been hinted at in the Future Enhancement notes on the V5 Architecture page but there is no specification however in theory such a module, with appropriate soft limiting, could adequately power 3+ 393 motors.

From a competition perspective teams really need either viable 393 motor control from V5 or a V5 Smart Motor Junior edition which is smaller and less powerful. This season seems pretty set in stone already and we’ll see what the future holds. Maybe next season only V5 will be permitted? Who knows how many more changes are in store.


Sell tacos on the corner, beg your parents for money, mow lawns, whatever it takes to buy V5 brains and motors for your competition robots. They are better than the 393s in every way, and you don’t want to use 393s anymore. (They are fine for classroom lab work, though.)


Even the richest, most powerful person on the planet could not afford a color TV in 536 BC . They weren’t available yet.


First, let me say this is in no way supported or sanctioned, will never be competition legal, and is generally not what you want to do.

With that out of the way, you can do it without a smart port expander. If you want to run a 393 motor (or any motor, really) at more than 5 volts but control them from 3-wire ports on the V5, the easiest way is to use a VEX power expander. The battery plugged into the expander will supply the power and the port will supply the control signal.

Again, this isn’t approved or sanctioned, it’s never going to be, and it shouldn’t be. So it won’t help the issue that @FullMetalMentor is trying to address. But it will let you run other motors from the V5 3 wire ports.


Interesting idea!

Okay, so I’m curious: why do you think your suggested technique shouldn’t be allowed? Are you speaking about this from a technical standpoint - like, some kind of strange surge might hurt the V5? Or are you talking about it from a moral or philosophical perspective or from some kind of aesthetic standpoint, perhaps?


Nor did I suggest in any way it was supported, existed or sanctioned. I merely suggested what would be required for 393 motors to be properly usable on the V5 since adding an EDR power expander with 7.2V battery is obviously never going to fly so didn’t bother mentioning it. If VEX did decide to produce a 393 motor expander for V5 smart ports we’ll let them figure out what’s competition legal.

On this page in the Future section you’ll find reference to a 3-wire expander. It’s undefined and could well be capable of powering 393’s if VEX figure it worth manufacturing.


Bigger, heavier and more power isn’t always the right answer!


I agree. It would be kind of nice to be in a situation where you did not have enough power to devote each motor to a specific job. Transmissions and clever gearing and interesting mechanisms have lost most of their meaning in vex. If you had 8 of the original plastic internal motors for this year, you would see a lot more impressive engineering to overcome the obstacles.


I agree with both of the above statements. For this reason in the past I’ve asked Vex to consider allowing things like thin, plastic-coated wire so the kids can experiment with smaller actuators. Building machines that rapidly handle mass quantities (which is usually what the designs converge upon) works well in many applications in the real world and especially in the Vex game designs but there seems to be little room for other approaches.


Short answer:
I think proper inspection of this would be tough. That’s it.

Aside from the possibility of mis-wiring, (which is difficult to do with a power expander) I don’t see any technical problems with it.

Sometimes, I don’t even use the power expander. (This increases the likelihood of screwing up.) Once you think about how the motor controller (MC29) works, you realize you don’t need a power expander to take control signals from a computer (cortex, V5, Arduino, RasPi, etc) and power from an external source. Systems have to share a ground reference in order to properly interpret the control signal; don’t forget to take care of that.

Again, no technical issues from this aside from potentially frying your computer from a wiring mishap.


My cautions were for my suggestion, not yours. What you suggest–use the port expander whenever they make one available–needs no caution.