Why are 393s banned when using V5?

In these months waiting for full sets of V5, and having to wait to put in our additional motor order since our motor discount is in our backordered V5 set (according to our vendor), I find it hard to understand why we cant use a few 393s to supplement incomplete sets of V5. Why can’t we compete with, for instance, 4 V5 motors, and 4 393s?

because they are basically useless. Those ports don’t have the same power output as a cortex has.

And even with using a power expander to provide the voltage to the motors, it’s still not ideal.

The bus that the legacy ports are on is only 5 volts and 2 amps. The 393s normally operate on nominally 7.2 volts from the Cortex. Two 393s will draw more than 2 amps and trip the circuit protection on the legacy bus. A power expander “might” help, but if iyou draw more than 2 amps from the legacy bus, it won’t work anyway.

The point of the power expander is that current for the motors would come from the power expander battery, through the power expander PTC, not the source of the PWM signal (Brain/Cortex). There’s no technical reason the power expander wouldn’t work just as well with V5 as with the Cortex.

As far as I see it, it’s “not ideal” only because it would be a kludgy combination of legacy and new systems (and I’m sure VEX has not and doesn’t intend to devote any resources to testing or supporting this configuration).

So realistically, they could have allowed the use of power expanders and legacy motors for just this season, if they had predicted that their suppliers would be incapable of manufacturing the new systems at a sufficient rate. I understand that they couldn’t delay the manufacturing of this platform since this game was made to show off the vision sensor, but it would have been nice to see them work with us a bit to make sure we get to enjoy this full season and not just the last month of it.

I haven’t tested the 393s with the power expander and V5. I am not sure what the ultimate power draw would be on the V5 legacy bus even if it is just providing PWN signal for 4-6 motors to the power expander. I do think that it is not something that they have tested much (if at all) and therefore do not want to recommend it.
As I understand it, the production holdup for the V5 Brain is due to the supply (or lack of) for a particular capacitor. This is an issue that several of my electrical engineer parents have heartily affirmed. There is a tremendous shortage of capacitors worldwide. I realize that this doesn’t change anything for us. I personally understand the desire to try to come up with a stop gap solution. I don’t have any of my V5 order yet either. On the other hand, I have been one of the lucky ones who had more Cortex systems than I have need to turn in for the buy back program.

I did some light testing and work with 393s and a Power Expander with the V5 and it’s workable for testing, but I’m not sure how it would help up in a competitive match, or a series of matches, particularly if I’m using more than say 2 motors for a variety of functions.

And speaking with my EE friends - the global capacitor shortage is bad. Really bad. Particularly if you need one very specific capacitor that’s hard to find. It’s an econ problem.

All of this has been an econ problem.