Robot hanging issues

Hi everyone.

I’ve been having quite a few issues with my lift for hanging lately and I’m wondering if I could have a bit of help.

I’ve attached 2 images of my lift towers, I have 4 heavy motors for the lift, 6 bar linkage arms. There are other teams who I have seen with the same gear ratios and arm style which can hang and I’m wondering if I am missing something obvious?

It can lift itself about 2-3 inches high, and then begin to fall back down.

The base is quite light so weight should not be causing a problem.

Thanks,
Marco

1 Full batteries.
2 Rubber bands pulling the lift DOWN.
3 More rubber bands.
4 Hanging hooks mounted close to the lift towers.
5 All bearings have nuts and bolts.
6 Motors are in High Torque mode.
7 Low friction. (Arm should move extremely easily by hand without motors and rubber bands.)

Hey Marco,

Firstly, you may want to double up the 84T gears in the towers to stop the teeth from snapping off. Just two gears side by side to make them the same thickness as the High Strength gears.

Where abouts are you holding the robot when you attempt to get it to lift itself? At the back or the front of the intake? It will be much harder from the back than from the front, somewhere halfway along should work well.

Check the friction on the shafts, but also on the rotating points along the arms.

~George

You should also try to put the gears closer to the motor, and try to make the towers as thin as possible in order to avoid twisted axles.

Hey George,

I have been thinking about doubling the 84T gears and will probably be adding one quite soon, next time I get into school probably (stupid exam study).

Well basically, if I hold the robot from the front of the scoop near the intake rollers, it will lift fine but will basically tip backwards which will be annoying for having to keep big balls in. If I hold it from the back, like I said on my first post it will raise a couple inches then fall back down. I haven’t tried from the middle.

Friction on the shafts and arms aren’t a problem at all.

Cheers,
Marco

Thanks, I haven’t had any problems with twisted axels all throughout this year with my arms lifting and being tested for lifting over the months.

Thanks for the tip of motors closer to the gears though, I may add extra gears on the opposite side of the c-channel.

1 My batteries have always been full when testing lifting.
2 I do have rubber bands on the lift arms pulling down but may be trying to add more soon.
4 Close to lift towers as in on the arms vertically above the towers?
5 All bearings have nuts and bolts.
6 Motors are in High Torque mode.
7 Arm is very easy to move.

I am just going to shoot in the dark but you are using aluminum right?
kind of a stupid question but I did miss this my rooky year :rolleyes:

Also it could just be old motors that have seen better days.

Haha this isn’t my rooky year :stuck_out_tongue: I am using aluminum and they are relatively new motors so they shouldn’t be an issue.

https://vexforum.com/attachment.php?attachmentid=7808&stc=1&d=1385078823
Your intake is attached at the red X on the blue bar. If you are able to get your hanging hooks mounted on the blue bar, closer to where the bar is powered, (e.g. where the green X is) it is better. While hanging, your arm will have much better leverage.
6barHangPos.jpg

Oh thanks for that, I’ll try get a CAD design done now, I’ll try post an image after.

Hey marco

I think you’re right to try and install another set of 84 & 12 tooth gears close to the motors as well. This will reduce the angular deflection of the shaft even if you are not seeing twisting all the way.

While it is not in the CAD model, do you have rubber bands/black tubing assisting the lift up that will be counteracting the lift on the way down (as you pull up on the bar)?

If you can have the rubber bands start counteracting the lift on the way up past the point of the 24" goal but before the high hang bar that might help. This way your motors have to work a bit harder to go up and grasp the bar at the end but it will start assisting you as you start the pull up. Of course beyond a certain point the rubber bands start to stretch again and hinder the pull up but hopefully you are above the wall at that point.

I don’t see a locking mechanism either. So you may just fall back to the ground once power is cut. Doh!

Glenn

Hey Glenn,

Thanks for the help, yeah I now plan to add an extra 84T on the inside of the C-channel as well as a metal 12T on each tower.

Yes I do have rubber bands on my actual robot, you can see them in this image here (it’s an old picture so the robot doesn’t have everything as you can see on the CAD):

Also heres a full CAD with a 40" pole visible to show how high it reaches:

I haven’t got a locking mechanism yet but I plan to once I sort out whether my robot can hang :slight_smile: I’ve got an idea of how to easily lock so no problems there!

Thanks,
Marco

Hi Marco

Your current rubber band mounting position (in the photo) is powering the arm up. This is helping you lift game objects, but is hindering you from hanging. To hang, you want to be powering the arm down. Try removing the rubber bands and hanging. If still no joy, change the mounting position so that the rubber bands are becoming more stretched as the arm raises.

Cheers, Paul

The bars on that six bar look a little close together for comfort. It could be that the lift is locking up at the top when you start to hang.
You could test this by trying to hang from a lower bar or give it a boost at the beginning of the climb.

Thanks Paul, I was planning to change the rubber band configuration lately and I’ll follow through with your tips.

Marco

Hi Max-D,

I did actually move my top 2 bars up one hole to test if it was locking up and it doesn’t seem to be a problem. If I hold my intake from the front next to the intake rollers, it does lift the robot. The thing is I’d like to lift the robot from further back along the scoop.

Thanks,
Marco

The issue with hanging farther back on the cradle is that you will be torquing it.

Here is an idea:
https://vexforum.com/attachment.php?attachmentid=7809&stc=1&d=1385133071
The orange string is connected to the dark red hanging hook and the dark gray lift arm. The hanging hook is velcro’ed to the light gray cradle.

This gives you much better leverage for your arm when hanging, but does not lift you as far. But that extra height is not needed.
LooseHang.jpg

Velcro’ed? You mean so it will detach from the scoop?

Marco

Correct. You don’t want to hang from the scoop. You want to get the hanging hooks that high, but you don’t want to torque (twist) the scoop that much.
Also, your arm has to output less inch-pounds of torque (power).