DR4B Geometry Calculator
A double reverse four bar reaches roughly twice as high as its bars are long. This works out how high, how low it folds, and whether it starts legal.
Inputs
Pivot to pivot on one bar. Both stages are assumed the same length.
Angle of the bars from horizontal at rest. Lower folds flatter.
How far the bars swing up. 90 is straight vertical and rarely reachable.
Floor to the bottom pivot, set by your tower.
Whatever the lift carries: intake, claw, tray.
Results
Vertical travel
—in
Height raised
—in
Top of the carriage.
Height folded
—in
Height at your chosen angle
—in
Ceiling if bars went vertical
—in
Folded inside the starting cube?
—
How this is calculated
A four bar swings its payload up along an arc, which means the payload also swings outward. A double reverse four bar stacks two of them with the second mirrored, so the second stage's outward swing cancels the first's. The payload goes straight up, and the two stages add their lift together.
rise per stage = bar length × sin(angle) total rise = 2 × bar length × sin(angle)With your numbers
Hence the rule of thumb: a DR4B reaches about twice its bar length. Twelve inch bars give roughly two feet of travel, from a mechanism that folds down to almost nothing.
Why the last few degrees are not worth chasing
Because rise depends on the sine of the angle, the gain flattens badly near the top. Going from 45° to 60° adds a useful amount. Going from 80° to 90° adds almost nothing, and buys it with the worst mechanical disadvantage the linkage ever sees, since the torque arm is longest when the bars are near horizontal but the leverage is worst near vertical.
Most working DR4Bs stop somewhere around 80°. The height you lose is small, and the mechanism is far better behaved.
Folding is the other half
The folded angle sets how flat the lift packs at the start of a match, and it is the number that decides whether the robot passes inspection. A lower folded angle costs you nothing in maximum height, since travel depends on the difference between the two angles, and it buys room for everything else.
The catch is that a nearly flat four bar has almost no mechanical advantage at the moment it starts to lift. That is why so many DR4Bs use rubber bands tuned to help hardest at the bottom of the stroke. TheRubber Band Assist calculator sizes and places them.
Sources & assumptions
The 18" starting envelope is from the Override2026-27 game manual. Everything else on this page is geometry from your own measurements, so there are no VEX figures to go stale.
Assumes two equal stages, equal angles, perfect pivots and rigid bars. A real DR4B flexes under load, and the two stages rarely track each other exactly, so measured height usually falls a little short of this.
The legality check covers folded height only. It says nothing about width, length, or any other rule an inspector applies.
- V5RC Override Game Manual v1.1 (2026-27) — checked 2026-08-17
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