The screws strip very easily, so I was trying to find an m2 self tapping screw with a thread pitch of .6mm, but all I could find was a .4mm thread pitch. Are these screws custom manufactured for vex, or is there anywhere to buy them or replacements for them (aside from the motor refurb kit)?
I do not know of any place to buy the motor case screws but here is a far easier alternative. Plus it is a lot easier to switch out the gears.
Since any M2 screw is legal, we use these. You will need another 1.5mm hex/allen wrench . So far 0 strips when changing internal gears using these puppies. You can almost guarantee one original screw will strip out using a #0 phillips screwdriver (the one corner that seems to have some loc tite on it).
10mm for the front covers and normal back covers (91292A011)
16mm for the IME covers (91292A002)
It makes for a much faster turn around time swapping out busted gears (the old powder metal ones that tended to break). Maybe a bit too soon to declare victory on the new style cast/cut gears but so far so good!
are there any problems with the screws coming out? It seems like there would be since the thread pitches are different, causing cross-threading. Does this happen, or are the original screws actually .4mm thread pitch? Also, what do you mean by the different metal gears? We have some older 393s (I think from gateway, maybe before). Are the new 393s superior, or are you talking about something else? Is it worth it to buy the refurb kit for all of the motors for the new gears, and should I replace them with the new ones before they break?
The screws are the same standard thread size. No problems to date with loosening or breakign or stipping (started this process in January so most of the season of abuse taken with no issues)
Last year Vex switched the internal gears from a powder metal gear to a cast gear which is much stronger but more expensive to manufacture. Maybe it’s a fully cut gear which is even more expensive to manufacture.
I would wait until they break to replace them. It takes a pretty heavy load to do this (a monster lift or setting two motors upon each other at full force on that monster lift)
Sorry for the upcoming pontification, but you asked…
With the old powder internal gears, your gears can end up splitting like this picture below. Notice the glittery/powdery look at the split point on the gear? In a cast one, you would see lines of fracture while in a powder metal the gears are pressed into this shape and fracture in smaller points since it is a bunch of smaller bits crammed together (think high pressure glue in a metal context). The new gears are cast and should theoretically have a higher stress point causing fracture.
In the cast gear, you need to finish off the teeth using gear cutting machines which are pretty darn precise. Pour hot metal into a mold that starts you close to the final product, then cut the teeth out and finish it off.
In a cut gear, you start with bar stock (extruded I think) and cut away until you get to the right shape. With a gear with two stages like the Vex oines, that is a lot of cutting to remove the metal before you start cutting the teeth.
The properties of the metal change as you do things like powder metal forming, casting, or extruding it. The recipie of the metal alloy is another factor. Your Sophmore & Junior year mechanical engineering courses cover this in a ton of detail. (Strength of materials, metalurgy, machines/dynamics, welding & casting, machining, etc.) In the labs you get to break stuff too!
Penn State ME '93 **We are!!! Penn State!! **(very nice effect when joined in by 110,000 of your closest friends)
To be clear, the new gears for the motors are all cut gears. They are not cast or powder metal. They are machined from a solid piece of steel, or in some cases, 2 pieces of steel and are case hardened to resist breakage.
They are much stronger than the original powder steel gears.
Thank you. That is very interesting.