Screw and a low profile nylock, tightened before putting it on the gear with some persuasion. Balance wasn’t an issue since it fit snugly against the gear.
Vex should make a 1:1 official gear cartridge, instant flywheel 
Idt that would be a “gear” cartridge
I found that the modified plastic lock bar slips when resistance is applied after it’s already spinning.
HS Shaft Collar worked fine for me but it had severe vibration and would come off if the motor was pointed downwards.
Possibly, the blue gear cartridge could be modified to remove the plastic ring gear teeth and fix the planetary gears to the carrier, making it 1:1.
We don’t certainly know if modifying a cartridge is legal but it is not considered a electronic part so possibly and hopefully that is possible
Based on the Q and A answer and the relevant rules, it seems to me like this would be legal.
Q&A 1115 Excerpt
"Is it legal to forego using a Smart Motor cartridge entirely? ... Technically, these do not violate any rules. However, it is extremely likely that any component that would interface with these components effectively without being assembled into a V5 Smart Motor would have to be fabricated using prohibited techniques, and would therefore be illegal (e.g. 3d printing, custom fabricated from parts outside the VEX system, etc)."The Q and A answer seems to imply that the smart motor cap and cartridge aren’t electronic components. Therefore, < R22 > would apply instead of < R20 > The general statement at the beginning of this rule seems like it would apply to the cartridge then. If this is the case, could we dissemble smart motor cartridges and use the gears inside them? Reusing the cartridge gears could better interface with smart motor cartridges used outside of motors.
This all seems to warrant another Q and A question clarifying the finer points of this application.
If you are wanting to 3d print custom geared cartridges, here is a link with the individual components to make your custom ratios.
This would, of course, only be legal for VEX-U
They don’t have to know do they now
One definition on “integrity” is to do what is right even if nobody is watching or you can’t get caught. The value of integrity is much greater than the value of winning a Vex game.
A new Q&A answer has made motor cartridges into electronic parts, so they may not be modified.
Note in Q&A 1115 it is simply ruled that omitting the cartridge is legal:
They do not state whether using a part to interface the gear will violate <R20.C.i>, so it is unclear whether interfacing a part with the motor gear is considered “replacing the motor cartridge”. Perhaps the GDC intended that teams who remove the motor cartridge may only allow the motor gear to free spin in the air.
In the 1115 ruling, there is a clause “without being assembled into a V5 Smart Motor”. It is my theory that as long as the motor is never “assembled” (whatever that may mean), parts may interface with the internal gear. Since the motor cap screws were ruled illegal to use for other purposes, it would be very difficult to attach a custom motor cap so that the motor isn’t “assembled”.
In light of all this, I find it strange that the GDC does not make things more clear by saying outright “all motors must be fully assembled and no modifications to the assembly can be made”. To squash all feasibility of a 3600 RPM motor seems to be the unstated intent behind these rulings anyways. VEX coming out with a similar part soon? 
Maybe everyone should hold their iffy Q&A’s until later when the rulings become more reasonable.
Aside from that
So how I was doing it before the ban was to remove the 3 planet gears from the blue gear cartridge and replace it with a custom cut Delrin part.
3600 RPM Motor Cartridge Drawing.pdf (577.3 KB)
To make it, print the attached drawing and cut out a template from the bottom of the sheet. Apply rubber cement to the cutout and plastic stock. Allow both surfaces to dry and press together. Center punch the marks, drill, and use a micro file to create approximate teeth, then cut out the disc. The 3 planet gears in the blue gear cartridge can be replaced with one of these, making a magical 1:1 cartridge. I spec a white color for the cartridge lid.
It has been some time since the post has been active, but it seems that there have now been teams at the signature events who have been using some flavor of no cartridge motors. Has vex done any more clarification recently? Has there been explicit explanations about having a piece inside the motor with the motor screws keeping the cap on?
Edit: For reference, some teams got past inspection with their flywheels not having cartridges in order to reach the proper RPM, so I was considering doing the same thing. But our team is worried it will cause a DQ.
The q&a’s that was asked regarding this topic make it quite clear that you can forgo the use of a motor cartrige.
Not since the post right before yours.
Read the Q&As 1115 & 1138 are the relevant ones which you can find linked in this thread many times.
If anyone is wondering how to make a direct 3600 rpm motor mount, this video walks through the process.
Wow so many awsome ways to make 3600 RPM motor mount. I would have never though of doing it this way.
People are actually using this? Competition illegal, in my opinion.
c. Teams may make the following modifications to the V5 Smart Motor’s user-serviceable features. This list is all-inclusive; no other modifications are permitted. i. Removing or replacing the gear cartridge with other official cartridges. ii. Removing or replacing the screws from the V5 Smart Motor Cap (276-6780). iii. Removing or replacing the threaded mounting inserts (276-6781). iv. Aesthetic / non-functional labeling (e.g. markers, stickers, etc).
Maybe this could use another Q&A 
On behalf of our referees, I just posted to the q&a to try to get a straight answer out of the GDC.
<R20c> Motor Part Removal : Robot Events seems controlling, in this question.
Technically, these do not violate any rules. However, it is extremely likely that any component that would interface with these components effectively without being assembled into a V5 Smart Motor would have to be fabricated using prohibited techniques, and would therefore be illegal (e.g. 3d printing, custom fabricated from parts outside the VEX system, etc).
IMO as an inspector, the technique demonstrated by @sazrocks (apologies if others were first), as well as other techniques using only vex-legal materials and methods, would be legal, given they are not “fabricated using prohibited techniques”. It would be my interpretation that the GDC intended to allow for cartridge-less motors, but did not anticipate how creative solutions could get.
R20 Clarification (Q&A 1115 and 1138 follow-up) : Robot Events seems to have also tried to get this clarity.
The problem is with this “non-answer” from the q&a (emphasis mine):
it is extremely likely that any component … would have to be fabricated using prohibited techniques, and would therefore be illegal (e.g. 3d printing, custom fabricated from parts outside the VEX system, etc).
So instead of answering “yes” or "no,’ GDC decided that ambitious high school students could not figure out a way to do it with legal parts, and thus did not need a straight answer. Furthermore, the word of the game manual to “replace a cartridge with another legal cartridge” (R20c) is problematic in the interpretation; although the use of the word “or” in the rule does seem to open the door for directly connecting a shaft to the pre-cartridge output of the motor. Our referees are asking for better clarification, since they officiate at multiple events in Michigan, and want to ensure an even playing field. It doesn’t really matter to us whether it’s legal or not, as long as we know for sure.
The GDC seems pretty clear that it is legal to not use a cartridge in a motor.
