# lift

were testong a lift on a bot and wantto know if it will work. We have a 6-bar and two 393 motors with a 1:5 ratio on each. how much will that lift at max motor speed? I know there`s some way to figure it out but im clueless at that, like trying to put the square peg in the round hole when all thats onboard is the peg.

https://vexforum.com/t/6-bar-formula/23669/1

Other things you need to consider is the weight of your arm and intake with how many objects you will be carring and if you are planning on useing the high speed gears for the 393’s. But if you have a pretty light arm I would say a 5:1 ratio with two 393’s should be fine especially with rubber bands.

If it’s well-built you should have no problem lifting your intake and the 6-bar as long as everything is aluminum and you assist it with elastic. It won’t be able to lift your base and hang, though. Were you wanting to be able to hang with it?

Just a bit ago, Jesse posted his robot which has an arm exactly like the one you’re talking about. So it’s certainly possible to built it and play the game.

If he gets around to posting the CAD (they have some on their website, but not of these robots), you could see exactly how it was build.

2059A has an arm exactly like you are thinking of, and from last week’s competition i would say it worked well.

There have been several discussions you can search for on the forums

If you figure 7 in-lb for a 393 motor that can help take into account all the friction points and staying away from stalling. Stall torque is just that - “stall”. So you want a good operating torque for a speedy lift, not a “barely lift”. Your max motor speed is affected by the torque required to move the arm. Lok atthe last like for rubber bands and convert to in-lb.

Use those figures to help decide gear ratios and how many rubber bands you need (and at what extended lengths).

You have to do the math now for the arm side of the equation, but from what point is your distance? Weigh the arm, find the balance point distance and that is the center of gravity there about and gets you the torque required to move the arm. You will now have to decide about the weight of your grabber and length of the arm as those increase the torque requirements the further out they are from the lift motors. (Rubber bands help a lot in improving this too, going to a 7:1 gear ratio gets you some more torque too but makes gear skipping more likely many times). Leave some room for the objects too as they do weigh something.

That should get you in the ball park.](http://design.caltech.edu/Archive/2001/handouts/Rubber_Bands.pdf)

totally forgot…

Here is the post with all of the pictures of our lift. It sounds like you have something very similar!

https://vexforum.com/t/323z-pre-warren-reveal/24820/1&page=2#17

Let me know if you have any questions.