I had not seen any videos of a double reverse four bar posted yet, so I thought I would share a video of a test robot we built using a DR4B. As you’ll see in the video, it was wobbly with one riser and when picking up two at a time, it definitely tipped over. We have a fairly big drivetrain base with rear wheel drive motors.
So the dr4b is something that may work for teams, but our current strategy is based more around skills and the need to pick up the two stacked risers at once, so I’m not sure a dr4b is going to work in our scenario.
Our next design we are going to try is a two sided scissor lift, with the rear being pushed forward with a horizontal linear slide.
I would recommend MUCH more bracing and more 2x beams instead of 2x beams. I would also recommend a longer drivebase, and making the support for the DR4B taller and further towards the middle. Also, if you used rubber bands on the DR4B with a slower gear ratio, you could really make your lifting power and speed better.
If you are planning on using a DR4B, you should try to lift one riser 3 high instead of 2, one high.
My team and I have made a DR4B robot and we were able to get it to 102 almost 103 in skills. There will be a reveal video for it coming soon…
You could try putting motors at the back of your lift, instead of at the base. This could give you some weight on the back so it doesn’t tip over. Definitely add some rubber bands.
@Noah10851B@AD1481@PenguinHasAGun - Thanks for the feedback, the videos might not have been the best representation of design, as we went through 3-4 design tweak’s and that was just the last one.
@PenguinHasAGun - we rebuilt the dr4b for motors on the back of the lift, but that seemed to struggle more lifting with risers on it (though it did seem better balanced obviously)
Where does everyone recommend putting rubber bands on a db4r design, I think that’s something we are struggling with on this design.
@Noah10851B - looking forward to your reveal, seeing another db4r in action will definitely help fill the gaps we might have in our design and build.
For my DR4B, I got a lot of inspiration from this thread: DR4B Tutorial by 333A. It covers just about everything you need to know about DR4Bs.
The main idea though, is that you want your rubber bands to be extended when your arm is contracted. This is true for anything that needs a bit more power.
@mizdared I should have explained what I meant by rubber bands. The idea with the rubber bands is to have them pull your lift up naturally. You want to arrange your rubber bands in a triangle. When your lift is down, the rubber bands should form a non equilateral triangle. When the lift is fully up, they rubber bands should form a equilateral triangle. Here’s some crappy images i tried to draw.
If I’m not mistaken, I don’t think it matters if it is equilateral when the arm is fully extended. I think the rubber bands need to be much less extended than before.
Rubber bands are literally OP. If you don’t have rubber bands on your DR4B, you are simply doing it wrong. (Mae this isn’t passive aggressive lol I’m just saying fax)
If you plan on going down the Douglas le Reverse Four bar route, I would highly recommend reading through this: DR4B Tutorial by 333A
But I would also recommend not building a DR4B for rise above, as it is much higher than it needs to be.
I heard that the point is to have the bands make an equalatireal triangle at the peak of the arm,for triangle banding. But the main i da ea for both is to have the rubber bands be farther apart at the bottom, ad very close at the start. That way the arm will be “wanting” to go up.
That is the point of rubber banding a lift in general. The point of using a triangle instead of straight banding it is so the rubber bands provide constant torque on the lift. With straight banding, as the lift goes up, the rubber bands get closer to one another at the top and have less torque on the lift. Though the bands do get closer to one another with triangle banding, the change in angle will keep the torque on the lift more consistent if done right. See the original UTRB post for a more in-depth explanation of why this works.
I gotta say, your tutorial on DR4Bs definitely was a life-saver. Thank you so much for spending your time contributing to the community and making that public for everyone!
