Author Topic: Robot needs to lift more than its own weight (Read 6277 times)

JonMarkGo · « **on:** January 24, 2008, 07:13:50 PM »

I have a robot made out of vex parts. I need to be able to lift an approximately 7-pound plexiglass box (no top or bottom). I'd like to use suction cups to do this. But with its current build, the robot doesn't have enough force to even get full suction against the box, let alone lift it back onto itself. What would be the best way to accomplish this, gearing it down or something else?

Trumpkin · « **Reply #1 on:** January 24, 2008, 07:22:54 PM »

can you build a robot built in the shape of a wedge to get under the box so that you don't need an arm?

JonMarkGo · « **Reply #2 on:** January 24, 2008, 07:28:26 PM »

It can be any shape I like but it has to fit within 30cmx30cmx30cm (the box). Basically the goal of the event I'm doing is to end up with a bunch of objects inside this box. The objects are easy enough to move into a 30cm space but I need to lift and lower the box over them, though at the end the robot can still be suctioned to the box if I don't have a way to remove it. Also, the box has 5 balloons inside that ideally would end up with 3 popped but still inside the box. 2 of the balloons have to end up outside of the box.

JonMarkGo · « **Reply #3 on:** January 24, 2008, 07:37:04 PM »

Well, the box is likely more like 2-3lbs. But I'm over-estimating a bit to make sure I can lift it.

Trumpkin · « **Reply #4 on:** January 24, 2008, 07:47:49 PM »

I'm guessing you start out with the box not attached to the robot? rather than building a suction cup strong enough to lift such a heavy box i suggest that you build an arm with a little shelves at the end and sides to scoop up the box and then you can raise and lower the arm to trap objects. I also suggest you make the arm as short as possible to make it more stable, also put most of your weight on the back. ( assuming your arm is in front)

JonMarkGo · « **Reply #5 on:** January 24, 2008, 07:50:22 PM »

The robot does not start attached to the box, no. And time is a factor, so it would likely take less time to push all the objects together and move the box on top of them than to move everything into the box. Here is the arena: http://www.soinc.org/events/robotram/RRplayfield08.pdf

Admin · « **Reply #6 on:** January 25, 2008, 10:54:32 PM »

Id make a robot like a fork lift . . . it uses compound pulleys to maximize gearing ratios . . .

JonMarkGo · « **Reply #7 on:** January 27, 2008, 06:57:50 PM »

I already have it all built with the suction cups. My main problem is that I can't exert enough force to get full suction on the box. The second problem is that it seems like the Vex servos just ARE NOT strong enough, even geared down, to lift the box.

Also, I only have a week...

JonMarkGo · « **Reply #8 on:** January 27, 2008, 06:58:47 PM »

Should I look into just using really high torque motors?

SmAsH · « **Reply #9 on:** January 27, 2008, 07:01:31 PM »

i would say you should. if your doing something like what admin posted

Admin · « **Reply #10 on:** January 27, 2008, 07:04:35 PM »

use this to help you calculate how to make your arm stronger (or what motor will work):
http://www.societyofrobots.com/mechanics_statics.shtml

JonMarkGo · « **Reply #11 on:** January 27, 2008, 07:05:37 PM »

I'm not using an arm or forklift. I just have a panel mounted to tilt back and forth (its mounted in the middle). Either way, I likely need higher torque motors... What about getting the suction itself to work?

JonMarkGo · « **Reply #12 on:** January 27, 2008, 07:09:49 PM »

Though that still would be helpful, I suppose. Here is a picture, I apologize for the horrible quality, it was taken on a phone... That panel on the right has 4 suction cups on it and its mounted on the two motors at the front on the right.

Admin · « **Reply #13 on:** January 27, 2008, 07:26:43 PM »

This panel, even though it doesn't look like an arm, can still be calculated as such. It has a pivot point, and so torque is applied.

You need to calculate torque:

torque = (mass of object) * (distance from pivot point to center of object)

Then just find a motor with torque greater than that.

As for the suction cups . . . perhaps add a bit of water to them?

JonMarkGo · « **Reply #14 on:** January 27, 2008, 07:27:45 PM »

The pivot point is basically the center of the object, I believe.

JonMarkGo · « **Reply #15 on:** January 27, 2008, 07:32:36 PM »

Water doesn't help, either. That was my first thought

ed1380 · « **Reply #16 on:** January 27, 2008, 07:35:40 PM »

if I'm seeing it right. the robot drives forward and presses into the box. then tilts it back a little and moves it. and you say the robot is too weak to push the suction cups into the box. right?

even if you solved that problem when the panel gets tilted back, wouldnt the box slide down the suction cups and hit the ground again since suction cups arent good with side to side motion

JonMarkGo · « **Reply #17 on:** January 27, 2008, 09:52:23 PM »

Yes. Its too weak to push the suction cups on. If I manually suction it on and tilt the platform back (without holding the box at all), the box doesn't fall off. The suction caps are pretty strong and the box is only like 6lbs.

gamefreak · « **Reply #18 on:** January 29, 2008, 06:29:53 AM »

I know that field, its from the scienece olimpiad which I decided to opt out of......

JonMarkGo · « **Reply #19 on:** January 29, 2008, 06:35:03 AM »

tjpark1111 · « **Reply #20 on:** January 30, 2008, 06:01:50 AM »

this is the main reason i didn't get a vex kit. i got two 1/4 scale servos up front with near 200 oz-in torque to do the same job as you did, and i think it's working pretty well. the nationals box with steel corner reinforcements is 5lbs 8oz. if your robot isn't strong enough to drive into the robot, figure out what other sort of attachments you can make to the box (strong double sided tape maybe?). well anyway i just got my parts today im in school right im gonna work all after school til like 10pm. lol the shits saturday we're so screwed.

Admin · « **Reply #21 on:** January 31, 2008, 09:06:58 PM »

Why not make that flat plate a scoop? Like just make it L shaped to act like a fork lift.

SmAsH · « **Reply #22 on:** January 31, 2008, 11:46:18 PM »

what! i thought that was what you were doing! ohh ok now i strongly agree with admin about that L

tjpark1111 · « **Reply #23 on:** February 13, 2008, 12:25:45 AM »

is there a guide that can explain how to build a forklift? or like how it works? im not really sure... because that would be EXTREMELY helpful.
and hey how did yours go mine did horrible cuz mine wouldn't stick to the box either. water didnt help. i wonder hwo the guy on youtube did it so effortlessly.

airman00 · « **Reply #24 on:** February 13, 2008, 05:49:29 AM »

a forklift has one ( or two) of these rack and pinion gears

The bottom gear is the rack which is mounted vertically and the top gear is the pinion gear which moves up and down the vertical rack.

Perhaps , you could write a guide on how to make forklift mechanisms on robots?

JonMarkGo · « **Reply #25 on:** February 13, 2008, 08:10:21 AM »

The competition is already over. I eventually got it to work using a sort of clamp on the top of my panel. But the robot ended up too heavy and its gears got caught in the playing field rug so it didn't move very far.

SciOlyStudent · « **Reply #26 on:** February 13, 2008, 10:08:47 AM »

I think I saw the same video of the suction cup robot you did. I'm pretty sure they used some type of suction system to stick the suction cups to the box.

ed1380 · « **Reply #27 on:** February 13, 2008, 03:21:08 PM »

actually IIRC a forklift has a vertical hydraulic ram with a chain thrown over a pully at the end of the ram. see pic for explanation

you could use rack and pinion but use a worm gear for it to act as a brake when motors are off

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Author Topic: Robot needs to lift more than its own weight (Read 6277 times)

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