I heared lots of different stories about using gears from different vendors on the same system. Eventhough the gears have the same DP and pressure angle, I know that they can have undocumanted different parameters.
If anyone had any experience with combining the gears from vex, andymark and rev, were there any noticable wear on short time or any jamming?
Depending on the answers we might consider using two Andymark 14t pinions with a vex 60t gear due to our current inventory.
You should not have any problems with that combination. Andymark and Vex are both (roughly) compatible with the AGMA gear standards, and should be interchangeable
[edit] That’s as long as they are both the same “pitch”. Andymark and Vex gears usually 20DP pitch, although there are some 32DP and metric gears out there, so watch out for that.
That’s not to say that they will all perform equally well. Vex aluminum gears in particular will wear pretty quickly compared to steel gears, especially an FRC gearbox, with poor tolerances, and poor lubrication. But given the short lifespan of an FRC robot, you’ll probably be OK.
It’s worth noting that Vex (and WCP) adds or used to add significant undercut to some gears to make them mesh better. AndyMark gears seem more standard. I probably wouldn’t mix manufacturers just to be safe, but if you do, make sure to add that extra 0.002" center distance. AndyMark gears are a lot less tolerant of poor spacing.
YMMV, but by the time you consider the slop in the hex bore of the gears vs their shafts, the slop between the shafts and the bearing IDs, and the slop between the bearing ODs and the (often but not always oversized) housing/plates, there’s usually more than 0.002" of extra center distance already between gears in COTSCommercial, off-the-shelf and custom FRCFIRST Robotics Competition gearboxes.
We always add extra center distance to be on the safe side especially on drive gearboxes. Gearbox plates are already machined but we don’t want to ruin our only suitable gears so we wanted get an opinion about it.
Be sure to account for the different widths and boss designs when mixing manufacturers. Don’t design all for one brand, and then just assume the other brand you have on your shelf will fit in without modification.
The other thing to watch out for is that the pressure angle is the same.
Luckily none of the FRC vendors use a different pressure angle from one another on any given DP.
I’ve mixed and matched gears from AM, VEX, REV, WCP, and SDP for years and years without issue. I’ve always done +0.002 to C-C distance, except when I’m looking for minimal slip on a slower rpm application (typically something I have absolute control on such as swerve steering).
Bonus advice, I would avoid running aluminum-aluminum gears, as not only will they wear quicker but you can also see some galling. Definitely recommend running steel-aluminum with steel being the smaller of the two gears, or just running steel for all. Now that multiple vendors have pocketed steel gears, the weight hit is pretty minimal and you’ll get much more lifespan and smooth running out of them.
We had VEX gearboxes during Stronghold, and aluminum-aluminum gears cost us at least a trip to the finals at Tech Valley – we knew they were stripping out, didn’t have spares, hoped they’d last and in the rubber match of the semifinals all we had to do was drive ten feet over level ground to park and we had the win…and the now rather wheel-like gears gave up the ghost, and we spun in place instead.
After that point we never used aluminum gears on mechanisms that would see a ton of use (like a drive train or shooter).
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