Hi, this year I am going with a double reverse four-bar. Does anyone have any tips on how to make it fast but also stable and strong enough to hold the weight of plenty of cubes. I plan to have four motors lifting on it.
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Aluminum screws are your friend, box screws are your friend, aluminum C-channel is your best friend, stable support towers are your best friend.
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Well yea I can see that being pretty obvious. The big question is if I should change the inserts in some or all of the motors
Are these v5 motors? If so, you do not need 4 lift motors, that is completely overkill.
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-Do not use 4 v5 motors, use 2.
-Focus on having seriously reduced friction so that the motors do less work.
-Do not use shafts, use screw joints.
-Make your lift as skinny as possible.
-Use rubberbands.
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Check out this thread: Refining our DR4B. It might save you from having to deal with some common problems.
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Don’t put the towers that the whole lift sits on at the very front of the robot or your going to run into some tipping problems.
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I would take a look at this thread: 929U Worlds Robot photos
929U had a great lift for Vex In The Zone.
Is there a tutorial I can watch for this?
I am also new to the concept and it would help our bot very much if we were to build one.
I’m not sure how one would make a video about what @Flip_Gunderson suggested. @technik3k posted a very good example of a DR4B in a thread about special partially threaded screws, and it worked very well for us when we tried it.
It is a well known “secret” among the veteran VRC teams that it is best to use single bearing screw joints when building 4B, 6B or DR4B/6B lifts.
With them you can achieve minimum slop, which translates into more stable lift that could go higher with more precision and less wobble.
When assembled correctly nylock nut is tightened almost all the way, but not fully such that you could still rotate the white spacer with your fingers.
To reduce slop and increase precision further you can use longer (2") screws. Below is a picture of the 2" screw tower connection for DR4B:
However, you have to be careful and need to regularly check those screws, because if they get bent you will end up with more friction losses than benefits.
Similarly, to reduce wobble you could increase the width of the arm/gear assembly in the mid-section. Here,1.5" screws hold an extra bearing on 3/8" nylon spacers (note that spacers are slightly rounded with a grinder wheel to fit the shape of the newer 60T gears):
On the other side of the gear keps nuts are used for better overall stability:
Washers are added under and over the keps nuts to get the perfect distance where c-channel is almost touching the gear.
This fits perfectly with 2" screw that acts both as a gear axle and rigidly connects both sides of the DR4B mid-section. Same as with the tower connection you need to tighten the nuts such that there is no visible slop, but not too tight, to avoid any unnecessary friction. After the final assembly you can use a small ziptie to add some white lithium grease lubricant under the bearings and onto the gears.
As you can see on the side view there is no need for any additional connecting hardware. Four 2" screws used as axles also connect the sides of the mid-section.
You can assemble top and bottom parts of the DR4B separately and then connect them at mid-section to get the optimal alignment between the gears.
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This. Your team needs to make flawless screw-linkages.
Perfect screw length, tighten down a keps, use a teflon washer, secure a bearing with the perfect length aluminum screw. Just make them perfectly.
If you do that, you can make a 4 bar, 6 bar, whatever, whenever. If you can make a perfect linkage joint, there is so much you can do from there on.
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Kepler Electronics did a very helpful video on the dr4b, on YouTube. I help me get a pretty good understanding of it.
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if im making a dr6b or a tripplereverse 6 bar the same joint concepts still apply correct ?
From what I understand, yes the concept of a DR4B is the same as a DR6B. except where you attach what is to be lifted, such as the intake is opposite.
Yes, but you might want to rethink your designs if you are making a triple reverse 6 bar.
You attach everything the same as you would on a DR4B. The only difference between a DR4B and DR6B is height (and the linkages technically) because 6 bars reach higher than 4 bars.
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what is the problem with a tr6b
It’s heavy, unstable and leaves you next to no room for an intake, not to mention you should never need to lift that high in this game and most likely all games in the future.
what do u mean rn we have a dr6b and it reaches 6 feet plus our upwards extending intake
but if we make a tr6b be can stack all the cubes
What I meant in that the top part of the lift would be on the opposite side of the robot.
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