A few questions regarding building a DR4B

Hi everyone, as we are starting to build next week, I am planning how things would work. We decided on a DR4B for caps. So we want to make a DR4B half the size of the chassis like this. And I saw in the video, they used 23 holes cut C channels for the DR4B. If we make a DR4B like that but with 20 holes C channels and 2 motors with a passive intake,

  1. Will it be able to sustain itself with only 2 motors and rubber bands?
  2. How do we make a joint for DR4Bs?
  3. Any tips of how we can make a good DR4B?

Thank you so much, I don’t have that much experiences with building but I have to lead the team so I’m kinda stressed.

  1. Yes, many teams have been using 2 motors latex-assisted DR4Bs throughout the past season :slight_smile:
  2. Powered joints definitely require axles because of the gears, but it might help to use screws for unpowered joints to reduce slop
  3. Latex assist helps alot in reducing strain on the motors, you might want to take a look at 3-point latex assist systems

To add onto what @rxian said, just make sure when you are building it you are carefully that you have some lifting room before you go over the 18” limit when not in the expansion zone

If you are using V5, then you should definitely be able to make a 2 motor DR4B

Yeah that would definitely help to prevent some unintentional rulebreaking haha

I guess the entire dr4b and its towers can be made shorter, honestly there’s not much need for them to be as tall as those of last season’s, also helps with what @Brad4478 said and saves weight :slight_smile:

@rxian Continuing on No. 2, what exactly do we need for the screw joints? So the screw head, then Bearing flat?, then Metal piece, then nut? Do we need spacers / washers? And if needed how many?

@Bhargav S. We are using Cortex due to motor limits. Hope we can make it.

@brad4478 Yes definitely, last year, our DR4B would not tuck down and our captain did something to it which I don’t know. He graduated now and we’re on our own!

@RougeScaless A general guideline would be to always mount bearing flats to the c-channels to increase stability, avoid metal-on-metal contact (i.e. put teflon washers between screwheads and metal pieces), and avoid tightening the lock nut at the other end too tightly. There are many ways to do screw joints, its always best to see what suits your robot best and adapt your spacing accordingly.

That’s a good video about screw joints. Personally, I’d only use axles when they are attached to motors, and the rest should all be screws. If you’re having trouble finding the right size then McMaster-Carr should have what you want.

To answer your first question: The robot you referenced, 202Z, did use only 2 motors on their dr4b along with with many other extremely good robots during In The Zone (929U, 8825S, 5225A, 8675A, etc…) so I would imagine that you would have no problem with a 2 motor dr4b. Even more so, that a Turning Point dr4b would be smaller than an In the Zone one.

For your second question: What I would recommend using are single rotating joints. The video from BNS shows them but in case you want some more detail you would firmly attach a screw to one of the bars with a fully tightened Keps nut. This will remove a lot of the slop and keep the screw perpendicular to the bar. Then you would run it through a bearing on the other bar so it can rotate, and then hold it all together with a Nylon Lock nut, just tight enough to keep it from coming apart. This joint only rotates in one place and you don’t have to compromise between a tight lock nut to remove slop and a loose lock nut to prevent friction.

Other than this I would recommend:

  1. Reducing friction to a point where if there are no engaged motors it is buttery smooth(no metal to metal contact, once your lift is to a point where it feels “frictionless” … it will never be frictionless but you get the point… add some white lithium grease on any rotation points or gears just to make it even smoother)
  2. Use rubber bands in a triangle shape to better the linearity of the force applied
  3. Only use aluminum. A light robot is a happy robot… just don’t use 1 by L channel on the bottom bars or on anything directly attached to a gear because in my experience it will snap
  4. Don’t use excess amounts of gears, you should only need a total of 6-12 gears depending on how you are powering your lift
  5. Have the top and bottom 4 bars directly connected to the gears transferring power from the bottom to the top.
  6. Bracing is your best friend. Use X braces on your actual lift bars (straight across bracing does basically nothing and bars in between a 4 bar do nothing)
  7. This is what I would say was most beneficial for me building a multiple dr4b’s all throughout Starstruck and In The Zone… STUDY! There are so many great dr4b’s that have already been displayed in the vex community so look at those.

I would look at these for help:

I would also STRONGLY suggest studying 8675A’s dr4b from ITZ because I was lucky enough to be able to feel their lift at Worlds and have never felt anything so close to frictionless

Other recently incredible dr4b’s that pop out in my head would be:
Skyrise: 118, AURA, 2915A
Starstruck: 134D, BNS
ITZ: 5225A, 8675A, 202Z, 2131, 1961U/X, 929U

Good luck! Let me know if you have any more questions!

@Avery_8675A pls leak lift.

I’ve been driving my world’s bot for 2 months now and my fully halfcut lift has never broken.
If you still don’t trust halfcuts on the bottom bars then you can use halfcut 3 wides. It’s noticably stronger and very unlikely to break.

What do you want to know about it?

@josh_siegel mentioned that your lift was nearly frictionless? Is there anything in particular that you guys did?

So there are two things that attributed to the low friction. One is how we did our banding. Also I suggest to use rubberbands over elastic tubing. Second is the screw joints. For the joints we used a variation of the single bearing joint showed above, also make sure to use nylon washers.

For the screw joints you need to use a nylock with some washers and then screw it on

You probably already know this but make certain to use supports on each four of the lift to keep the dr4b from leaning.