PDA

View Full Version : How to do a Forklift type robot.


team2061
01-14-2008, 11:26 PM
My team wants to go with a forklift type robot but doesnt know how to achieve this. can someone please help?

Jaybee1405
01-14-2008, 11:43 PM
There's two ways to do it:

1. Continuous (preferred): You line up vertically stacked 8020 in front of each other (we'll say 2 for simplifying the example). A cable runs from the base of the back 8020 to the top of the back 8020 (through a pulley) and then down to the bottom of the front 8020 (another pulley) and is then tied to the top of the front 8020. You put a motor with a winch near the base of the back 8020 (which is bolted to the robot's frame) and when driven, it will lift the front 8020. The front 8020 will slide up and down, and you can mount any type of forks on it. This isn't true "continuous" because you're relying on gravity to pull it back down, so it's much better to have it continuously looped and powered.

2. Cascade: Four 8020 stacked vertically next to each other. Cable starts at bottom of back 8020 on winch with motor. Cable then runs to top of back 8020 (through a pulley), over, and then under second-to-back 8020 (another pulley) and then tied to bottom of second-to-front 8020. Another cable is tied on top of second-to-back 8020, looped under second-to-front 8020, and then tied to bottom of front 8020. Et cetera! The cables become taught and push up the 8020 in front of them.

These are both very simple methods, and I know I made it sound very complicated. If I had pics I would show you, but I don't.

Good luck,
Joe

Jaybee1405
01-14-2008, 11:56 PM
also, see http://www.chiefdelphi.com/forums/showthread.php?t=61407

ZakuAce
01-15-2008, 12:03 PM
There's two ways to do it:

1. Continuous (preferred): You line up vertically stacked 8020 in front of each other (we'll say 2 for simplifying the example). A cable runs from the base of the back 8020 to the top of the back 8020 (through a pulley) and then down to the bottom of the front 8020 (another pulley) and is then tied to the top of the front 8020. You put a motor with a winch near the base of the back 8020 (which is bolted to the robot's frame) and when driven, it will lift the front 8020. The front 8020 will slide up and down, and you can mount any type of forks on it. This isn't true "continuous" because you're relying on gravity to pull it back down, so it's much better to have it continuously looped and powered.

2. Cascade: Four 8020 stacked vertically next to each other. Cable starts at bottom of back 8020 on winch with motor. Cable then runs to top of back 8020 (through a pulley), over, and then under second-to-back 8020 (another pulley) and then tied to bottom of second-to-front 8020. Another cable is tied on top of second-to-back 8020, looped under second-to-front 8020, and then tied to bottom of front 8020. Et cetera! The cables become taught and push up the 8020 in front of them.

These are both very simple methods, and I know I made it sound very complicated. If I had pics I would show you, but I don't.

Good luck,
Joe

You're number 2 idea is what I want to do, but our team leader doesn't want it because he doesn't like the possibility of it binding. Just throwing that out tehre as a possible con.

vivek16
01-15-2008, 11:34 PM
what are the pros and cons of each of these types?

thanks, Vivek

octothorpe
01-16-2008, 12:53 AM
These are both very simple methods, and I know I made it sound very complicated. If I had pics I would show you, but I don't.

Here's a picture that someone posted to illustrate the two types:
http://www.chiefdelphi.com/forums/attachment.php?attachmentid=2834

Somewhere on Chief Delphi there's a powerpoint explaining the advantages and disadvantages of either type. I think Continuous is the most common and pretty clearly the better of the two (it's the version my team is considering). As far as I can tell, Cascade uses more wires, requires the up wire and down wire to move at different speeds, and causes each of the elevator segments to lift sooner (meaning a higher CG and thus more instability at anything less than full extension).

M4 Sherman
01-16-2008, 12:57 AM
Whatever you do, dont use draw sliders! My team did that last year, and it worked terrible.

Cory
01-16-2008, 01:01 AM
Here's a picture that someone posted to illustrate the two types:
http://www.chiefdelphi.com/forums/attachment.php?attachmentid=2834

Somewhere on Chief Delphi there's a powerpoint explaining the advantages and disadvantages of either type. I think Continuous is the most common and pretty clearly the better of the two (it's the version my team is considering). As far as I can tell, Cascade uses more wires, requires the up wire and down wire to move at different speeds, and causes each of the elevator segments to lift sooner (meaning a higher CG and thus more instability at anything less than full extension).

That was Chris H. You can find it here (http://www.chiefdelphi.com/media/papers/1322)

Justin M.
01-16-2008, 09:13 AM
You can also use a dual acting pnuematic cylinder to move a forklift up and down. Of course you'll be be limited to the maximum stroke length, so you'll only get fully up or fully down. But since you only have one fixed height to lift the ball over this year, pnuematics may be the way to go. There much simpler and are more robust that using a motor, then you need to worry about things snapping, backdriving, etc. You needed precise control last year because there were three different heights of spider legs, this year it's just one height.

lukevanoort
01-16-2008, 09:45 AM
Whatever you do, dont use draw sliders! My team did that last year, and it worked terrible.
Assuming you mean drawer slides, I couldn't disagree more. Last year, my team used heavy-duty ball bearing drawer slides that we got at a local hardware store (you can get similar off of McMaster-Carr; but Home Depot, Lowes, etc. don't carry them) and it worked beautifully. The friction was very low and we never had any binding problems. 217 and 229 used server rack slides in 2005, and that also worked very well (where we got the idea, actually). I think 111 may have used something similar in 2005 as well (their linear bearings look very similar anyway, just much larger). I imagine that if you used bad drawer slides (like those from Home Depot) that they might not work well; however, with some decent slides they work great! If I was building a elevator this year, I would either make it like the how Poofs/RAWC did last year, or with drawer slides. Those 80/20 sliders, while quite usable, IMHO, just don't compare to the smoothness and low-friction of running on ball bearings.

BTW, I would be careful about using pneumatics for big actuations... it may look like there is a lot of air stored on the robot, but a 24" stroke cylinder can blow through it pretty quick. Imagine this: you're in match three of the finals on Einstein, you're trying to stick the ball on the overpass to seal a win and your air runs out :(. Constantly running the compressor will heavily eat into your battery life, too. Don't get me wrong, I love pneumatics for short, fast actuations (like a gripper or shifter) or even one-time/very infrequent large actuations (like ramps last year or unfolding a mechanism), but I just wouldn't use them when I need a big-bore, long cylinder to do a job that needs to be done many times.

Justin M.
01-16-2008, 07:12 PM
Our "forklift hybrid" will run off of pneumatics, with a compressor onboard. I was weary of the air running out too, but we all came to the consensus that pneumatics would drastically simplify the design. Plus the "other part" of our manipulator uses up a good amount of motors that would drive the forklift. With the compressor, and constant replacement of batteries, we should be fine, hopefully.

cobrawanabe1699
01-16-2008, 09:39 PM
Careful with the weight of a forlift. That's alot of aluminum on the front of your bot. See my post in the contact patch thread.

vivek16
01-16-2008, 09:51 PM
"wheelie bar" as seen here: http://www.chiefdelphi.com/forums/showthread.php?threadid=61840

would probably be a good idea to consider...

-vivek

M4 Sherman
01-16-2008, 09:53 PM
Assuming you mean drawer slides, I couldn't disagree more. Last year, my team used heavy-duty ball bearing drawer slides that we got at a local hardware store (you can get similar off of McMaster-Carr; but Home Depot, Lowes, etc. don't carry them) and it worked beautifully. The friction was very low and we never had any binding problems. 217 and 229 used server rack slides in 2005, and that also worked very well (where we got the idea, actually). I think 111 may have used something similar in 2005 as well (their linear bearings look very similar anyway, just much larger). I imagine that if you used bad drawer slides (like those from Home Depot) that they might not work well; however, with some decent slides they work great! If I was building a elevator this year, I would either make it like the how Poofs/RAWC did last year, or with drawer slides. Those 80/20 sliders, while quite usable, IMHO, just don't compare to the smoothness and low-friction of running on ball bearings.



Yeah, We used got some heavy duty drawer sliders from Lowes. I think the specs on them were 4 ft. at 50-75 lbs.. All the little plastic pieces broke and the sliders started derailing. But Im sure the McMaster-Carr ones are more durable sliders.

chinckley
01-16-2008, 10:13 PM
Careful with the weight of a forlift. That's alot of aluminum on the front of your bot. See my post in the contact patch thread.

Where is this post??

Cory
01-16-2008, 10:16 PM
Careful with the weight of a forlift. That's alot of aluminum on the front of your bot. See my post in the contact patch thread.

Depends how you made it. Our elevator last year was not cg biased towards the front.

cobrawanabe1699
01-17-2008, 05:44 PM
Contact Area and its Relation to Friction? It's under technical discussions, and not too far way from this thread. I'm on page 2 or 3

bobdahaxor
01-17-2008, 06:15 PM
I saw the binding post, and yes it can bind. There is a rule of thumb though, each extension should go 1/2 of the previous. Like if you stationary bar is say 5 feet, then the second bar should extend only 2.5 to 3 feet. This will prevent binding. Our team used 8020 last year for our arm. It worked well, but you gotta follow that rule! Also use a CIM motor or Van door motor. Nothing else has enough torque to do the job in my experience. (Burnt up a geared down mabuchi. Poof!)

EricH
01-17-2008, 06:20 PM
I saw the binding post, and yes it can bind. There is a rule of thumb though, each extension should go 1/2 of the previous. Like if you stationary bar is say 5 feet, then the second bar should extend only 2.5 to 3 feet. This will prevent binding. Our team used 8020 last year for our arm. It worked well, but you gotta follow that rule! Also use a CIM motor or Van door motor. Nothing else has enough torque to do the job in my experience. (Burnt up a geared down mabuchi. Poof!)You can also rig to pull down. And the FPs have plenty of torque using their stock gearbox and no further reduction other than a winch. Been there, done that, didn't burn up the FP.

jferrara
01-19-2008, 10:13 AM
Hey guys, our team is incorporating a forklift design into our robot. We are unsure of what material to use, since 80/20 might be too heavy and will cause us to tip over. We need to support the ball and a rather large manipulator, which would potentially require a strong and sturdy elevation system. Has anyone used any material in the past that has been effective and fast? Thanks in advance.