Double-Wide Plastic Gears

In another thread, the suggestion was made that the current method of combining two gears is adequate and that metal gears would be a better solution.

If you examine a paired set of gears closely, you will probably find that the two halves are slightly out of alignment. When you mate them, the other pair will also have this problem. Together, the four independent parts create unncessary friction/binding in an assembly that is already under significant stress. Eventually they wear unevenly or deform slightly around the axle–either of which creates play in the system and makes them more prone to slipping or stripping at the axle connection. A single molded part would mitigate some of these problems.

Metal gears would obviously have a stength advantage, but they would require an entirely seperate development and fabrication process. On the other hand, existing CAD drawings for the plastic gears could be modified in a matter of hours, sent out for molds etc, and then put into production on the same line that is used to fabricate the current parts. In my mind, this simplicity (and cost advantage) outweighs the benefits of metal gears, but I am certain that VexLabs can perform this analysis much more precisely than I can.

The real point being that we need stronger gears of some sort.

here, here! i would like to see stronger gears, but i dont know about metal ones. i like the idea of a thicker gears, that could be used in transmissions.

Check out the gearing on the shoulder of 1114’s arm. It’s hard to tell from this angle, but they double geared their arm and placed a washer in between to take away the gap between the gears.

Metal yes, double wide no. Metal would solve many of the problems that might require double wide gears. If you would have to use a double wide metal gear then either you are over building or maybe it would be a good idea to rethink what exactly you need to do. In the end if you still decide you need a double wide gear then put them together yourself.

There have been applications in the past where I’ve needed to double up gears; not because I was shearing gear teeth left and right, but more of a safety measure to prevent such from happening. In all the Vex projects I’ve ever built, I’ve only broken a single gear; and that was because I did not yet have limit switches in place to stop the [massively geared down] arm from over-driving.

If you double up your gears and/or use sensors to limit your mechanisms from over-driving, then I don’t see much of a need for metal gears. If your robot needs metal gears, you should probably rethink and redesign your mechanism, as by that point it’s probably becoming a safety hazard. (If it breaks doubled-up plastic gears, it’s probably capable of hurting your hand.)

Our team doubled up gears and reinforced the centers of the 84-tooth gears by screwing on metal bar locks. Once we did that we never had a problem of a single gear tooth breaking or any center holes stripping. I think the gears they have now are more than sufficient. However (and this is a thread to itself), a consequence of this setup is we would slowly twist the axle over repeated use.

I think artdutra has a good point. There are limit sensors that most people don’t use that are in the kit, why not use those?

(Hint: You can put the limit switch on the arm, so you don’t have to find obscure ways to mount the switch on your robot.)

I agree that double wide gears would be advantageous and extremely easy to produce making them a viable product. However, given the option between plastic and metal gears I’d choose metal every time. All of the plastic gears will eventually deform while metal never would, so double wide gears used in transmissions would eventually fail to be as effective. However, metal gears would never, ever have this problem. So while I’d like to see metal gears more than double wides, I’ll agree that they would be good to have.

i think the plastic gears are fine you just need to be careful how you use em
i wore down the shaft of a 60 tooth on this one bot that i never took picture of(sadly didnt have camera)
but wat really needs to b made metal is the chain cause the one side of chain kept breaking on my wheelie bot for some reason:(

I am not sure where you find this information. But there are critical flaws in these statements. I’m not here to flame but mearly to point out that yes even metal gears have flaws and failures.

Any given item made of any given metal have flaws. These flaws may not be aparent. From hairline fractions to air traped into the mold or pour. These stress points can cause devistating disasters. Its not uncommon knowledge that metal is stronger than plastic. that gold is softer than stainless steel, and so on. But even though the application is less work you will still need lubrication to extend the life of a metal gear. Even metal gears wear down and misaligned ones even faster.

Honestly if your buiding with Vex then you don’t need metal gears. I would like to see the gears 3/8 of an inch thick thought instead of 1/4=2/8. There is alot of play in the vex system backlash if you must and that extra 1/8 th coushin would be nice but no need to double up. If you need that kind of power well your just not wanting to win a tournement… your trying to save the day. where in that case the vex is just too low powered.

I love the Vex system and i would not have many changed made to the existing componets. they are designed to work with the other parts not against them. and if your having difficulties with them it’s time to rethink the design.

Yeah, a little news update-I just broke a 12 tooth gear!! two of the ridges snapped off because my robots arm jammed into the metal base of the robot. Too much torque, I guess.

I completely agree with this! I was let down by VEX when I got my Chain and Sprocket Kit, thinking it was metal chain, and finding out that they were SO cheap that they made it plastic!

I have at least 5 pieces of my chain broken because of this

It’s very hard finding uses for chain/sprokets when the chain is plastic.

Whenever you use a 12 tooth gear you must double or triple them, or prepare to have gear pieces in your eye. When have destroyed these gears and they can fly out and hit people, there IS a reason they have us wearing safety glasses while competing.

  1. How would you adjust the chain if it were metal? It would be possible if it were made like, say, size 35 or 25 chain, but then it would be impossible to work with.

  2. If it continues breaking, try using larger sprockets. This will spread the load out on the chain.

  3. If the chain is still breaking and not slipping, then you probably are using the chain for something it can’t handle. You could try doubling up the chain or replacing it with gears

The chain works just fine when used properly.

so you’re asking me to go on ebay and buy lots of 10 gear kits for $79.95 plus $12.95 shipping?

sorry for lashing out on you.

I have an advanced gear kit and gear kit coming in a day, so i’ll take your advice in the future. Thanks

I’m just saying that you have to be expecially careful with the 12tooth gears and when you use them in high torque situations double them up so you DON’T have to buy more.

yeah thanks for the advice.