More Hanging Problems!!

We have a competition on Saturday and our supposed to be perfect hanging mechanism lifts itself two inches off the ground and the gears start clicking and we find a bent axle.

Help Please.

Six bar with 1:9.375
Rubber Bands going down
13lbs total weight


If you post pictures of your lift/robot we can help you more.

Unfortunately, the robot is at school. The hook is mounted to the back of the intake tray. Looking at it, it is pretty similar to your own bot Jesse. We have the intake offset so it is flat at the bottom and steep at the top.
There are 4 spaces between the top and bottom bar.

Make sure your towers are close together and your gears line up properly. You are geared 1:15 with high speed motors right?

I am not sure why you are having problems with hanging as hanging can be done with a 1:5 ratio lift.

In fact we have 4 393s on the lift. We currently have just under 2.5 inches between the towers. Would you say that that is too much.

I’m assuming four 393 motors on speed with compound gearing, 1:3 and then 1:5?
edit: Got ninjad, looks like I assumed correctly :smiley:

Compound gearing is notoriously difficult to build correctly, especially when you’re trying to lift 13 pounds with it. Do you have the seperate ‘stages’ of gearing between seperate verticals, or the same verticals?
ie. does your lift look like this:
or like this?: [
(Apologies for the crude diagrams, my paint skills need improving :))

I have found in the past that the second option, without an extra vertical, results in the lift clicking due to the greater length of unsupported axle when lifting heavy weights. The first option provides better support for the axles meaning the gears are more likely to stay meshed. You also want to make sure that the verticals are as close together as possible. If I recall correctly this is a gap of 2 holes for the lower stage that the arm is not attached to, and a gap of 3 holes for the upper stage that the arm is attached to.

However, I think you might be better off to try build a lift at 1:7 (four 393 motors on torque using 84 tooth gears) if you have time, it will be a lot easier to build and maintain, and should still lift a 13 pound robot fairly easily. Bolting two low strength 84T gears together is fairly standard practice to make a 84T high strength gear.

If you want any more help or have any questions just let me know. Good luck!](

I have the second one. I will try to fix it tomorrow.
Thanks so much

This is sort of what Telemascope was describing, also, do the 1:3 before the 1:5.

Make the axles as short as possible (between the supporting bearing flats).

Build quality matters, everything needs to be very rigid, lots of support between the tower uprights.

Hi JPearson.
What is that gear ratio in that picture

and is that a toss up robot

I’m pretty sure that’s 1:3, 1:5

The lift is geared: 2/3 and 1/5 which equals (I believe) 1/7.5.

first stage is 36 tooth driving 60 tooth, so 3:5, second stage is 12 tooth driving 60 tooth, so 1:5. Overall that’s 3:25, or 1:8.333. We would usually reverse that and say 8.33:1.

There is some more information on this robot in this thread.

and some more information on compound gearing in this one.

No, it’s not a toss-up robot (or in fact a competition robot of any sort).

Sorry to bring this thread back up but:
We are thinking about doing a 6 motor drive and a 2 motor 1:7 lift. Would that be enough for hanging with an 14 lb robot?

Also could someone tell me the formula to find the proper gear ratio depending on weight and arm length?
Thanks in advance

Hey Jesse, could you possibly hang with 4 motors on torque with a 5:1 ratio lift?

-2H :slight_smile:

With 9.375:1 gear ratio and 13 pounds robot, you should have no trouble to hang if you configured them correctly. The compound gearing is more difficult to build than simple one as Telemascope said . You can add an idle gear to reduce the possibility of the main axle bending:

idle gear.jpg

We had this issue with our robot at Conroe due to our lift drive gear being cantilevered. Once we mounted a 25 hole bar with bearing blocks to the outside to give the drive gear support it solved our problem. Given the performance of 9090C I would certainly listen to Tiger.

To clarify, we ditched the compound gearing and we are currently using a 1:7 gear ratio with HT motors. For our last competition we had 4 motors on the drive and 4 on the lift, but as we are most likely using pneumatics and 2 reservoirs, the robot will be a 1lb and a half heavier at least. Therefore, we want to allot two of the lift motors to the drive so our robot can push/drive better.

We want our catapult to flip up, attack its hook onto the hanging bar, and flip back down, therefore lifting the robot by 4 inches or so (hopefully this will work). We also are seeing whether we can raise our robot with a 1:7 gear ratio with two HT motors and rubber bands probably helping it raise.

We also do have a pinion gear (idler) on either side of the 84 tooth gear We would probably leave it there to prevent axle bending. Thanks for the suggestions though.