Using elastics in scissors lift and elevators

I heard a teacher is using scissors this year for skyrise. And with the help of elastics he can let the lift go up in seconds.
Can anyone tell me or show me some pictures of how elastics are used in elevators or scissors. Any help is appreciated. Thanks:):slight_smile:

Alrighty… here goes my paint skills!

[ATTACH]8438[/ATTACH]

So what you can see here is a scissor lift (black lines) both at lowest height (left) and max height (right). The red dots indicate where the elastic bands would be mounted and the blue lines represent the rubber bands.

Basically, if you want elastics to help your robot lift, they have to be stretched out at min height so that when your robot lifts, they pull back inwards which, from where your bands are mounted, help pull the scissor lift up.

This is just a really basic drawing showing an example so don’t go ahead and put elastics where I have, for one, this many rubber bands is a bit overkill and you’d need your motors powered hard to keep the arm down.

Hope I helped somewhat and for more help, just send me a PM or email :slight_smile:
Scissor Elastic.jpg

Actually that may rubber bands is not overkill…

Using them on multiple levels helps even out the top levels too from being uneven compared to the bottom ones.

What about this type?

This reduces the shape change of rubber bands and they are tight from bottom to top.

https://vexforum.com/attachment.php?attachmentid=8439&stc=1&d=1403289424
scissor elastic.jpg

Yeah, If I were to tension a scissor I’d do it like this just so that there’s so much more of a linear like amount of tension.

There’s also very little mechanical advantage… so your linear tension is doing less.

That’s when you pile on more rubber bands to compensate.
In the end the only problem is that there is a lot more stress on the structure of the scissor lift, but the advantage of uniform like tension can outweigh that.

I agree. I guess for this year we possibly have 5 stages, and you can evenly distribute rubber bands on all ten of your crosses. Still that sounds like a lot of tuning.

The tuning is not bad. Rubber bands are easily added and removed from levels to distribute the load. Much easier than tuning the black tubing.

You’ll get the hang after a few weeks.

One last tip. Either leave the scissor extended up for storage or take off the rubber bands from week to week. They tend to permanently stretch if you leave it in the down position.

Thanks for the tip. In toss up we did not even think of taking off elastics on our eight bar, and although it did not affect a lot because we had four motor lift, the elastics did lose power drastically. So i guess i gotta design the lift so that standardized rubber bands can be added on and removed easily. That does sound a lot better.

Thanks for reply. And can you explain a little further on what is “little mechanical advantage”.I do not really understand how it works. :confused:

Thanks for the photos. No doubts on your paint skills.

Here’s a helpful link for when you are calculating how much help you are getting from your rubber bands.

mechanical advantage is how much force or power your are getting out of your work

For example, if you have a motor with 1ft-lb of torque, and it goes through a gear ratio of 1:3, you will have a mechanical advantage of 3, and outcome torque of 3ft-lb, because your motor’s torque is getting multiplied by three through the gear ratio. Of course, that comes at a cost of a reduction in speed by 3.

I still haven’t been able to quite understand why people use thousands of elastics instead of latex tubing? The only advantage I can see is that they are easier to tune, but with the tubing you can change them as well and make custom lengths. The tubing also wears a lot less than elastics and is stronger, so you don’t have your robot leaving behind a trail of broken elastics and they don’t loosen over time.

And for those people who haven’t heard of latex tubing, I would highly recommend you look into it, even if elastics stay the main source of tension.

Latex Tubing has to be ordered online for the most part vs #32 rubber bands which are available at Walmart. Rubber Bands are a uniform size while most tubing has to be made at custom lengths. Tubing is too much trouble.