This is really interesting. People are saying it’s probably illegal, but I’m interested to know if it’s not. Ngl, I would love to see some guy make a 25200 rpm drive.
That’s because it is. RTM
That wouldn’t have enough torque to drive.
<R20> point C (emphasis mine)
Teams may make the following modifications to the V5 Smart Motor’s user-serviceable features.
No other modifications are permitted.
i. Changing or replacing the gear cartridge with other official replacement cartridges.
ii. Replacing or removing the screws from the V5 Smart Motor Cap (276-6780).
iii. Replacing the threaded mounting inserts (276-6781).
Since the adapter isn’t a “legal cartridge” I’d assume this is illegal. But maybe someone could ask on the Q&A just to confirm.
It’s to bad if it’s illegal it has so much potential.
Could one argue that the motor is in a state of cartridge replacement? If replacing the motor cartridge is a legal process, the motor is legal at any point during the process, including with the cartridge removed. Making something out of VEX parts is not illegal, so I would argue that this would be a legal usage of Smart Motors.
I’m with taran on this here. If it’s only made out of vex parts (which I think it is) it’s probably legal, we should ask on Q&A though idk how to do it.
In the change up Q&A that is the kind of language they chose to use in regards to the motor cap screws
Not installing the mounting screws that hold the V5 Smart Motor Cap in place would not be considered a “modification”. It is more along the lines of “not fully replacing a user-serviceable part”. Although partial reassembly is rarely advisable, this is not prohibited by the linked response or by R22d.
But I think they clarified the wording this year to make it extra clear that the motor cap screws are the only motor parts that can be removed during a match. This also lines up with another VEX U change up Q&A that applied to VRC where they specified that removing the motor caps is specifically not legal, so I would draw the conclusion that would also include motor cartridges.
Modifying, removing, or custom-fabricating (such as via 3D printing) V5 Smart Motor Caps would not be legal in VRC.
Granted previous Q&A responses no longer apply, but they are generally a good indication of the GDC’s intent.
I don’t believe this would be legal, as much as I would like for it to be. If you read c. i. :
Changing or replacing the gear cartridge with other official replacement cartridges.
One can argue that you are replacing the cartridge with a vex legal part, and not an official replacement cartridge, meaning that the whole “i’m in the process of replacing the cartridge” wouldn’t fly. Also, , use common sense.
If I was reffing a competition, not legal, team gets sent back to the pits. Sorry, @Sylvie
Uh, no? Replacing the cartridge is legal, but I see no reason that would imply that the motor is legal after you’ve started replacing it but before you’ve finished.
I might add that if you ask on the Q&A you will probably get the perfectly satisfactory answer of
No.
Y’all are absolutely zero fun.
It would be nice for this to be legal, but sadly the rules make it a pretty difficult argument to make, even if there is some room for debate.
I didn’t say it wouldn’t be fun. I wish it were legal, because that would take less space. Nevertheless, I can’t imagine they would let it pass at a tournament, so I’m not going to put it on my robot that way, and I’m almost positive you aren’t either.
Being rational is not the same as zero fun.
As generally established, this is most likely illegal. It could however be an interesting part that vex could produce. They could make a new motor cartridge with a 1:1 ratio (direct connection)
In the newly answered Q&A #1115, altering a motor in this way seems to have been legalized. However keep in mind that it is extremely unlikely that there is a legal technique that can interface with a V5 Smart Motor using legal methods 
. This Q&A also seems to imply that you can alter V5 motor cartridges as long as you alter them using legal parts. Points 3, 4, 5, and 6 seem to state that only the actual motor part of the cartridge is an electronic component, and thus is the only part that can not be modified. However, a counterpoint could be made that points 3, 4, 5, and 6 are referring to that parts that are only used for mounting the smart motor (the cap and threaded inserts) are legal to modify. Either way the idea of using 1:1 direct flywheels is very exciting and may allow for new and more compact robot designs. I would like to see other ways that people will attempt to modify their motors to be able to mesh with the internal gear, so please post them below if you have a new design and are willing to share.
Seems like it’s possible then. Gdc will not stop us from direct driving our motors >:)
Here are some pictures of a theoretical way it could work, legally and using non-custom parts. All you need is a single hs clamping collar, a 1/8" shaft insert, one 1/2" spacer, one 1/16" washer, and a shaft to make it work!
I gotchu fam.
Part 1: regular HS shaft collar
This one can be improved by tightening the HS shaft collar tightly, so the collar can hug the motor a bit tighter. I didn’t tighten mine all the way, so that’s why it slipped off. Thanks @sazrocks for the tip.
Part 2: low profile HS shaft collar
Part 3: modifying old lock bar.
Cut the sides off, and attach to motor
It doesn’t slip under load ( I was running it at full power while blocking its motion)
This can definitely be improved by cutting the lock bar so that the mounting holes are partially there, allowing for a gear mount of some sort.
Part 4: 4 post hex retainer
Hollow out a 4 post hex retainer with a 1/4 bit, and shove it on. It sticks relatively well, and as a bonus you can put some c channel on there.
However, machining lexan pieces might be the best bet for these.
It also looks like the weight is not well balanced when using the clamping collar. The nut throws the balance off by a bit, it seems. That’ll probably end up bleeding energy and reducing efficiency.
The HS clamping collar method works pretty well.
So I drew up some custom polycarb pieces that can be used with the lock bar. I personally will probably use the lock bar method. The sketch I did uses two lock bars: one at the bottom that locks with the gear, and another on top of it with the 1/8" shaft insert in it. There are still some small details to fix, but it’s looking like a good option.
How did you tighten the collar there?
It can’t be screws since that seems to make the whole thing unbalanced