Compound gears

How high can I make the ratio of my compound gears on a motor 393? We are
Trying to create a 4 bar that lifts up a skyrise cube and because we have a limited number of motors, we are using a compound gear system. But when we try to lift the arm, we are having problems. There is a lot of clicking on the gears and it looks like power is an issue. Can you please help us? Thanks!

You should post pictures of your setup, so people can make better suggestions.

If you are just building a 4-bar to lift a cube, then compound gearing probably isn’t necessary. You may want to add rubber bands:)

If gears are skipping, then you probably need to better support the axles.

Thanks for the quick response. I’ll post an image tomorrow. But, is there a limit to how much torque one motor can handle?

Well, there’s the stall torque, which can be found on the product page. So, yes, there is, but gearing the motors will increase the output torque (that is assuming you are gearing the motors to reduce rpm).

Try and keep the poor little 393 under 7 in-lb of torque to not get into trouble with the PTC tripping.

See this post for some ideas.
compound gearing post #1

You will generally run into mechanical issues, axles twisting, things like that, if the ratio is too high.

thanks for all your responses. Im a first year coach and I am struggling with curriculum and parts. To the first post, attached is the link for two of my students’ robots. I would appreciate any advice. thanks.

It’s hard to see, but it looks like you don’t have any bearing flats ( part number 276-1209 ) supporting the axles. The gears should probably be attached to the arm as well, not sure that’s even possible with this version of the gears though, often we use the alternative “high strength” gears in this application. The axles will also tend to flex in the middle with this configuration, but sort out the axle support (ie. the bearing flats) first and see what happens.

Which state are you in? Any chance you are in SoCal?

Maybe the quickest, easiest fix would be to apply some rubber bands to help the motors lift. Note that it matters how the rubber band is angled with respect to the robot’s arm, otherwise instead of assisting in the lift, rubber bands can do the opposite. You also want each side to have an equal number of rubber bands, and make sure whatever the rubber bands are hooked onto is secure and won’t fly off and smack somebody in the face. Take a look at the rubber bands on this arm:

After that, I would suggest that you use plastic bearings to avoid any metal-on-metal friction with the shafts. Bearings also help keep C-channel perpendicular to any shafts that are passing through them.

Also, in your first video, the bottom motor’s shaft does not seem to have anything actually “trapping” the shaft in place. The addition of a shaft collar on the inside left face of the vertical support should help keep that shaft from eventually wiggling out.

Im not positive but do you have a motor attached further up on the gear train? did you do that for a reason? because you are minimizing the effectiveness of your gear train. ideally you should connect both motors to the same shaft. and that shaft should be the one at the very beginning of the gear train

thanks for all the advice. I feel like an idiot. To jpearman, im from HI.Too bad we couldn’t hook up. I will definitely get some bearing flats on their and a lot of rubber bands. I will also put the motors on the same shaft and see what that does. thanks for everything people. I appreciate it.

We are. :slight_smile: We all are at the very beginning. I have an engineering background but it still took me an embarrassingly long while to get into the Vex mindset, to get at least somewhat familiar with the capabilities and limitations of Vex components, the software, the tricks of the trade, etc. And every game is different. Every game flushes more and more of my ignorance out into the open for my kids to see.

Here’s something I said halfway through my first tournament. (It’s something my kids quote at me every time I forget something or they prove me wrong about something):

“Competition template? What’s a competition template?”

Thanks for your response