Catapult/Lift Torque Design Discussion

VEX V5 General Discussion Technical Discussion
#1

Hi guys,

I wanted to ask a very simple (I think) question about the torque of a lift.
Which of these methods of attaching the intake is the most effective. I am looking primarily for which one will require the least amount of energy to pull down and to lift up.

#2

Also, how do I add images. When I tried to attach the files to my previous post, it said the file is too large. I don’t know how to use the image tags either. Please help

Thanks

#3

Upload them to a site like imgur and post the url between the image brackets like so:


http://i.imgur.com/VQKuSkz.png

That code would come out like this in your post:

#4

Maybe try scaling down the image. I’ve never had issues with posting pictures, so if scaling it down doesn’t fix it, its possible that it isn’t working because of whatever problems the vex forum is having right now.

#5

Is there another way to upload the pictures without having to upload them to imgur. I just don’t want to have to create another account and more passwords for me to remember.

#6

I tried scaling down the image as well. Even that didn’t work.

#7

I use post image a lot, and that doesn’t require an account or anything

#8

Ok I think I got it. http://imgur.com/a/Ws2au

#9

Does that work?

#10

So here is what I wanted to say in my original post:
The green lines represent the chassis and the tower. The blue line represents the intake.

Let’s use a catapult as the example for this scenario:
Does the position from where the intake is attached and how steep it is mounted affect the amount of energy (in # of rubber bands) required to launch? Does it affect the amount of energy (using motors) required to reset the catapult (pull it back down)?

#11

Effectively, no. Using very approximate physics, you can prove this. (I can post the “proof” here if you want)
All you care about is the lift height and the velocity of the objects when launched. As long as the launch angle is optimal, how steep the lift is doesn’t matter.

#12

Sort of. The length of the arm and the number of degrees that the lift has to rotate affect the energy required. In all 3 of those images, the arm length and angle vary, so the energy required would vary as well.

#13

If we think about it, which one would need the least amount of rubber bands to move the fastest? My guess would be the second one because it has the shortest arm to lift and move. The shorter the arm is that needs to be moved (resulting in a lighter arm), the less air resistance and drag caused by it. That would then cause the motors to have less stress to hold it down because less rubber bands are needed. However, that is my thought process. Does anyone have a different idea or thought?

#14

I think it is a trivial difference that could easily be accounted for with appropriate tuning.

However, I would think that if you have a longer arm, the bands can stretch a longer distance, and so you might be able to get a faster movement simply due to the extra stretch length. Obviously a large amount of it depends on how heavy the thing you’re lifting is (objects + intake), how well-built the arm is (no sideways flopping), etc.

#15

I am not sure air resistance is going to play a significant role as the speeds the arm would be moving is slow enough to make drag due to air resistance negligible. Not meaning to troll, just sayin’

#16

Thats a fair point. You’re right that the arm is moving pretty slowly regardless since it is still just a few small rubber bands so air resistance isn’t really a major factor. However, doesn’t the amount of weight of the arm have a role. Even slight increases would make a difference in the speed of the catapult since it is moving so slowly in the first place, right?

#17