Do DR4B's Need Counterweights?

[SiliconOxide]

Our comp is 1/16 but no time to work during break

[SiliconOxide]

Also where would I put rubber bands on the DR4B? We don’t want to stall the arm motor if possible.

[64540A]

DR4B Rubber Banding

So I know that the general consensus for rubber banding a DR4B is that a triangle is the best shape. However, I have a few questions about some more technical aspects on the choices that teams make when rubber banding their lifts. For one, why do most teams only rubber band the bottom part of the DR4B? I’ve been rubber banding both the top and bottom four bars and it works just fine, so is there a particular reason that the bottom is usually the only part rubber banded? Also, why do most teams…

There are tons more threads abt rubber banding. This is just one of them

[2775Josh]

Check this out:

Delta IV Iteration 3 Close Up

Two-point linear rubber banding on both sets of four-bars will be the best for your lift.

[SiliconOxide]

Thank you very much!

[Anomalocaris]

Here’s an accumulation of many useful rubber banding threads on the forum

[SiliconOxide]

Who are you? Are you like DRow?

[Anomalocaris]

No…

[SiliconOxide]

ok can you post pics of Uniformly Tensioned Rubber Band System Analysis/ Guide I can’t see them

[Anomalocaris]

Here are all the pictures from @therealcedz’s two posts in order of appearance

[SiliconOxide]

Thanks! Is 2 point linear banding the best option, or a triangle?

[Anomalocaris]

It depends on what you want to accomplish. Personally, I like triangle banding better, but both have their advantages.

[SiliconOxide]

I think we just need the arm to stay where it is at all times. (even though we haven’t finished building the DR4B) should we use triangle?

[64540A]

Banding is meant to help ur lift go up against gravity. If u find a sweet spot for rubber bands, u might be able to accomplish what u want. If that’s too difficult, u can set up a simple pid loop that keeps the lift at a specific height by putting a potentiometer on one of the axels and adjusting the degrees

[64540A]

Forgot to say this but I’m pretty sure u can’t use the internal motor encoders cause those don’t record their value between matches. They will reset to zero if u turn off and on the robot

[SiliconOxide]

Uh I kinda need help with coding now. I’m not the coder (now I am bc the coder is so lazy). This is my 2 month of Vex so Idk what to do…

[LilTree]

Well what are you trying to do?

Edit: Wait, are you sure you meant to type that in this thread or the other one?

[SiliconOxide]

oops I meant the other one

[Anomalocaris]

@64540A

If that’s too difficult, u can set up a simple pid loop that keeps the lift at a specific height by putting a potentiometer on one of the axels and adjusting the degrees

I would argue that a pid loop would be harder?

@64540A

Forgot to say this but I’m pretty sure u can’t use the internal motor encoders cause those don’t record their value between matches. They will reset to zero if u turn off and on the robot

This doesn’t necessarily matter as long as the lift starts at the same place every match. Even if it’s off by a degree or two, it won’t make much of a difference, especially if the lift is on a 7:1 ratio.

Instead of pid however, you could simply use brakeType::hold to hold the lift in place. This Should Not replace rubber banding though; ideally you would use both, but rubber banding is more important.

[64540A]

Thanks for correcting me about the internal encoders. I’m not too knowledgeable abt them. I usually don’t talk abt things I don’t know abt but u just wanted to propose an option.

I also agree that brake type hold is not a replacement for banding and can easily break motors.

Lastly, I’ve had enough experience with pid to a point where it is actually easier for me. It all depends on the team