It is that time of the season when beginner teams are searching for resources to assist them with building their first DR4B lift, and senior teams are looking for new ways to build taller, stronger, and more stable DR4Bs, improving on their designs from past seasons.
Hence, we decided to make this DR4B Tutorial by 333A.
- In our guide, you will learn how Double Reverse Four Bar (DR4B) works.
- New teams will find step-by-step instructions how to build a good DR4B.
- It explains the main factors of stable DR4B: Screw Joints and Cross Bracing.
- This guide shares building tricks we’ve acquired and the lessons we’ve learned.
- Other references are linked for teams to research and improve upon our design.
Finally, we are working on a video counterpart for this guide, which will be found here upon its completion.
Some highlights of the DR4B/8B that we built at the beginning of the Tower Takeover season:
These are bearing extensions on the rotating bars of the lift. They extend as far as possible while still allowing the screws to go through both sides of the midsection. This minimizes wobble as much as possible:
These are some of the bracing techniques we used, namely X Bracing and K Bracing. They both use triangles to reinforce the lift, since triangles are the only rigid 2D shape. This prevents a lot of torsion that would otherwise become a problem:
This is the rubber band triangle on the bottom linkage of the lift. Using a triangle formation allows the lift to raise with uniform acceleration, which allows for more consistency in a competition. We but them around loose spacers to allow the rubber bands to rotate without the risk of snapping:
DR4Bs are very useful lifts for VEX Robotics. In addition to being extremely tall, they rise linearly, making them useful for almost any challenge involving lifting objects. It’s clear why they dominated in past games such as In The Zone and Skyrise. However, in order to be competitive, they need to be built with maximum stability.
The most important takeaway from our research was that you should use screw joints whenever possible. This change had the greatest impact on the stability of our lift, and forever changed the way we build anything.
Bracing is also very important, and can’t be overlooked. There are many effective ways of bracing, and all of which have their respective benefits.
Lastly, we learned to not fear the unknown. Had we not tried new things, our lift would still be a twisted wreck that lifted at an angle. Learning more about DR4Bs has not only improved our lifts, but all other aspects of our building.
Remember that there are many great methods for building DR4Bs, not just the one presented in our document. Each one has its own merits, and learning about new methods will help improve your own.
Good luck with your future endeavors!
- Team 5225A - The Pilons (check out their ITZ season DR4B CADs)
- Kepler Electronics Video (great explanations, but axle shaft joints may wobble)
- Comparison of VEX joints (spoiler alert: @Owen thinks screw joints are the best)
- @technik3k mini-tutorial (on how to build rigid DR4B lift using 2" long screw joints)
Recent DR4B discussion topics: