forklift system trouble!
 

Team 3329 has decided to use a forklift system to pick up game pieces. the system will be on an incline and the grippers (more like spreaders) we want to be able to articulate like an elbow to pick up pieces on the floor. the trouble comes with how to get the actual lift to lift. What materials do we use as rails? do we use pneumatics or motors with belts or chains? i've searched all over and am having no luck finding anything...

Re: forklift system trouble!
 

Go to www.8020.net and look at the Extrusion Aluminum Series 10. MSC sells the stuff. Then take a look at the Double Flanged LInear Bearings or Single Flanged. They ride up and down on the Series 10 Extrusion 1" Width. That's the stuff you need. I have been using it with my team for the past 2 years.

Re: forklift system trouble!
 

Most lifts are of two types CASCADE or CONTINUOUS and they are moved up and down with a cable or in some cases a chain...

They are not real difficult to undertake but do require some calculations to determine the tension in the cables because it is not as straight forward as you might think.

We are making ours out of square aluminum extrusion...with chain for the bottom section and a cascade cabling system for the top three sections.

Send me an IM with your email and I can send you a workshop set of slides about mechanisms that might give you some ideas...

We will use two 550 motors with a transmission and a chain reduction to power ours up and down.

Remember you must (if you want it to work well) Power the lift UP AND DOWN...

Friction is a killer as well as racking concerns.

We actually made a lift in 2008 out of a ladder but wouldn't recommend it... (too heavy)

Make the upper sections lighter than the lowers if possible... and keep everything that is moving as LIGHT as possible...

let me know if I can help more..

Re: forklift system trouble!
 

We are planning on doing a Continous ladder system, but are not powering it down. We are using Delron pieces, with nylon washers to separate the pieces. What trouble will we have in using gravity to get it back down?

Re: forklift system trouble!
 

First, what if down isn't down any more, and you need to retract your elevator to get it out of the way?

Also, you are limited to moving at less than the acceleration due to gravity on the way down. You can't go down any faster than that, and if you try to go too close, you risk having your belt or cable that is holding the elevator up fall off the pulleys.

If you bump around on the field, you risk your elevator bouncing up and the string coming off the pulleys.

If you forget to release the tube from your grabber and try to lower the arm, you risk the string coming off the pulleys. (And this will probably happen at least once.)

For us, that's too much of a risk and loss of performance for saving the simple cost of stringing the return cable. Preventing the string from being able to ever come off the pulleys or get tangled would help address some of these issues.

Re: forklift system trouble!
 

http://www.alpinerobotics.com/images...bui.php?page=2

here is a pretty good image of what we did in 2007, it worked really well and we have basically duplicated the lift, our team has been refining the lift design there for 4 different challenges, 2 by 1 by 1/8 c channel is used for the rails, with bearings and washers on shoulder bolts to slide along it, all the stages are driven by one input, on that year it was a pair of r550's in a 48-1 reduction, this year it is a FP in a dewalt , (anti back-drive pins intact) be sure to allow a little flex because the extruded channel is not perfect.:ahh:

Re: forklift system trouble!
 

In 2007, we used a forklift that was supposed to use gravity to go down but found that friction was way too much. We used aluminum tubing and even when placing slick plastic and a ton of lubricant it simply wasn't enough to make up for the friction. If I was ever going to use such a system again, I'd use bearing of some sort or power the downward system too. Our robot went up whenever we wanted, but then we was stuck up for the rest of the match making our offense useless.(though it did play a part in a defensive strategy)

Re: forklift system trouble!
 

We are designing a 2 stage telescoping lift for our 2011 robot. The sliding interface will just be box tube with teflon tape. It will be driven by a closed belt loop in serpentine fashion and powered by a single FP. Ideal calculations show that it can reach 12 ft/s, so we are shooting for closer to 10 ft/s.

Re: forklift system trouble!
 

A few pictures of our lift from 2008:
http://www.chiefdelphi.com/media/photos/30267
http://www.chiefdelphi.com/media/photos/35975
http://www.chiefdelphi.com/media/photos/35974

See here for a more detailed explanation of how it works.

Re: forklift system trouble!
 

I just want to add my voice to the "if you want movement in any direction, it needs to be powered in that direction" chorus.

Re: forklift system trouble!
 

Please email Team 1758 your slides. We have used articulated arms in the past but want to try a forklift system this year.
Thanks Jim Johnson jejohnson@fsd1.org

Re: forklift system trouble!
 

Our 2007 forklift used Bosch Rexroth extruded aluminum (similar to 80/20, but metric) with delrin sliders and slider carriages.

We used Rexroth sliders again last year for our lift, and it was tremendously reliable.

Re: forklift system trouble!
 

how do you get the elevator to lock in place once it has reached its desired height? we are using a pulley system to make it rise, but dont know how to lock it in place to prevent back drive.

Re: forklift system trouble!
 

that's a problem our team is going to be tackling in the very near future :)

One solution, which we used successfully in 2008, is to provide a small amount of power to the drive motor for the elevator to hold it in place. While this works, it stalls the motor, which is less than ideal (and may lead to a burned out motor!)

Another solution is to introduce enough friction into the system that it needs to be powered down. For example, using a gear box like the window motors have allows you to easily power the lift in either direction, but the screw can't be back driven, so the elevator won't come down on its own accord.

Yet another solution is some sort of independent braking system. A friction brake, like you see on most bicycles, could be made to work fairly simply. Likewise, boat winches often have ratcheting action that can be turned on and off, or set for forwards or reverse, and could be adapted to work.

Re: forklift system trouble!
 

use your window motors and it wont back-drive :p