Gears Scipping & Gear Ratio

My team and I are having some difficulty’s with our gears skipping. When we first started running our robot with a load (yesterday) we only skipped if the arm became over extended, but now it skip’s every time its raised in the begining. We are running a 25-1 (I think) gear ration with two 393’s. Lifting around 9 to 10 sacks with the help of rubber bands. Its kinda slow too, so if anyone knows a way to speed up the lift; please shair. I would be great full
Some pictures are below, if you need any other views just ask!
https://plus.google.com/photos/106840872679038552786/albums/5836080351141806913?authkey=CIPO29a8rbmaXg

You can try adding the 1x25 bars in the very center of the gears. Also, i think you might be able to turn the outermost c channel 180 degrees to minimize the length of the axle. With the change though, you may need to use the small standoffs to mount any metal. Also, make sure the rubberbands aren’t overstretched. Rather, use quantity. The more you stretch out your bands, the more power you lose the higher it goes up. If your team can afford it, make sure you use aluminum for your intake and lift. Other than that, try to minimize the amount of metal you use. If you have an excess of bracing, you may want to remove a few pieces and strategically place it.

What kind of arm system did you use?

Put space between the gears. They are causing unnecessary friction. Also you don’t need that high of a gear ratio. To lift that small ammount of sacks.

It’s probably skipping a lot now because you bent one of the axles. Look to see which gear is skipping, and replace that axle with a straight one. To avoid this problem, do the things mentioned above, and also know the limits of your lift, and try not to lift more than that limit

How can we reduce our gear ratio? If we go to a lower one it just sags down. Do you run your motors at half speed to keep it up? or what?

You need to actually change your gears. Instead of using those big gears(60 tooth), you have to use the slightly smaller plastic ones(the 36 tooth). If you use the 30 tooth, you may want to apply lockplates like 24c to prevent skipping. However is you find sagging as a problem, you can add a part in your code where the motors are powered slightly. Not enough to raise the lift, but enough to prevent it from going down. I don’t think you’ll have lifting problems. I built a double reverse 4 bar with a 5:1 torque ratio and it could lift like 5 sacks

So should we try to change it to a 9 to 1 with the lock plates in between all the axles? O and when you say lock plate do you mean these? Drive Shaft Bar Lock http://www.vexrobotics.com/vex/products/accessories/structure/275-1065.html

Yes. if you look at the last photo [here, it shows nice use of lock plates to prevent skipping. You could also try 15:1, but i think 9:1 should be fine.

Note: Competitionwise, you should be good with a 25:1 lift system, but changing ratios wont really affect your skipping problem. using the lockplates on a 9:1 system is like using a 25x1 bar on a 25:1 lift system](“https://vexforum.com/t/24c-omnomnom-2-0-post-rex-tournament-reveal/21770/1”)

What compound gearing would you use to get a 15 to 1 while using the shaft bars?

For 15:1 you need a 12 tooth connected to a 36 tooth. Then on that same axle, use a 12 tooth. That 12 tooth then connects to a 60 tooth for your 15:1 torque. You cant use lockplates on the 5:1 ratio you created, but you can use it on the 3:1. However if you link the lock plates together using a bolt, making it reach further, it may work

K thanks, we will try a few of these things hopefully something will put an end to this skipping!

Our team made a video about gear skipping. Hopefully it should be helpful.
http://www.youtube.com/watch?feature=player_embedded&v=YrEfxDRlTLo
Maybe you can help counter the down-voters :slight_smile:
http://forum.robotevents.com/design/entry/detail/3372

Some compound gearing examples.

https://vexforum.com/showpost.php?p=317337&postcount=1

You can also achieve the same ratios without using the turntable, for example, here is the 8.33:1.

[ATTACH]7117[/ATTACH]
compound_gear_8_1.jpg

I see two more things you could do. Supersonic sparks idea of the metal holder is a good one I had not seen before.

You can also reduce the wiggle room of the axles by using shoulder screws on the Delrin bearing blocks. The shoulder screw will jam right up against the metal creating less wiggle room fro the screw to pop the axle out. Make sure the screw is coming through the metal first to get maximum contact. You may also need to add another piece of metal for the screw head distance.

The other downside is that you hammer the shoulder screw into the block it widens the block out making it not so good for their proper use in the future.

Shoulder screw product page

It also looks like you used a frame rail to attach the motor and used standoffs before you put the bearing block on. That could add some wiggle too. Could you flip around that frame rail and attach the motor a bit closer to the gear? Maximum tighness is what you want in this gear train.

Last part is I don’t know if being at 3:00 on the motor’s driving gear versus down at 6:00 makes a difference. If you are in line vertically you are in one single dimension to control skipping. That first 60 tooth gear has the y-axis for it’s drive pushing up/down on the second 12 tooth gear while the original dirver is on the x axis for the driven gear pushing that forward/backward. That means the middle axle needs to hold both positions versus just staying in line vertically. Not sure if that makes a difference or not.

Over on the 944B progress thread, there is a link to a video where i explain how we overcame our gear skipping problem!