I am not exactly new to VEX, but very new to the concept of a reverse double four bar lift. I would very appreciate it if anyone could provide information on the subject, so that we may wreck the opposition.
Watching this youtube video can help you understand the basics about the DR4B:
Here is my ITZ robot which was a cross between a dr4b and a 6-bar.
My tips for you are that you need to keep everything consistent, both sides need to be cross-braced or connected together in some way or form. This year if you are expecting to lift more than a few cubes you will need 2 100RPM motors and probably a 1:7 ratio. I would personally power the lift from the middle section much like the ITZ robot I linked you instead of powering it at the bottom like the other video.
If you have high strength shafts I would use them especially this year because of the weight being carried by the lifts, just be sure not to rely on them and instead rely on x-bracing.
Here is an album of pics of our worlds ITZ robot, many of which show the DR4B. I’d recommend you take a look at the methods of attaching elastics, how we braced it, and the different ways of saving weight (depending on how you’re planning on using it). A major factor in our design was the thinking that we’re only using it to lift one cone at a time, which is fairly light, so we don’t want 5lbs of overhead; this thinking may or may not carry over to the current season, depending on what you’re thinking of for design.
This advice has been exemplary in providing us advice about how the concept works and how to build one. Thank you so much! One more thing: where is the best possible spot, for the most power, to mount the motors?
Well, I looked at one of this year’s robots for one of our district’s “pro” teams, and they had a mechanism where they could grab a whole row of cubes at once and tilt them into stacks. Or grab stack by themselves. Sorta like a very tall claw. I was thinking of doing something like that; mounting the mechanism on top of the DR4B. Would that be too heavy?
People have put both trays and passive cube tubes on DR4Bs and they work, but you might have to use 100RPM motors depending on how heavy the lift is.
My tray lift bot’s upper lift assembly was very heavy. I didn’t realize it till I took apart my lift. I’m not sure of the exact number, but maybe as high as 5 pounds for the 4 section tray, tilt, and intake section as well as the lift arms.
It’s not an issue because you can use rubber bands to offset the weight when lifting empty but unless you design well you might have trouble offsetting large amounts of cubes
11495B used a 100RPM lift last year for their cap bot at the world championship last year and they actually didn’t feel the loss of speed. They found that the increased acceleration and stability of the lift more than made up for the loss of speed.
If you were looking to grab a stack of cubes at once I would suggest a cube clamp similar to this one. It’s quite simple to add to a dr4b and I imagine it’s quite good with tower scoring.