Tipping & Wheelie Threshold
How hard you can accelerate, brake and turn before the robot goes over, and whether it will tip at all or just spin its wheels first.
Inputs
Whole robot with the lift lowered. From the Center of Gravity calculator, or balance the robot on an edge and measure.
Everything, including the lift and whatever it carries.
Arm, carriage and load. Set to 0 for a robot with nothing that rises.
Lowered position to raised position. This is what shifts the CG upward.
Horizontal distance from the balance point back to where the rear wheels touch.
Same, forwards. Equal values mean the CG sits midway between the axles.
Left wheel center to right wheel center.
Sets how much acceleration the floor can actually deliver.
Results
Can it tip at all?
—
With the lift raised.
CG height, lift raised
—in
CG rises by
—in
Wheelie threshold
—g
Accelerating forwards.
Nose-over threshold
—g
Braking hard.
Sideways threshold
—g
Acceleration the floor can give
—g
Equal to the grip figure.
Steepest ramp before it topples
—°
When you would use this
Our robot tips forward when we stop with the lift up.
Enter your centre of gravity height and the distance to the front wheels. The nose-over threshold is how hard you can brake before it goes over, in multiples of g. If that number is below your grip figure, the robot tips before the wheels slide.
We keep doing wheelies when we accelerate.
The wheelie threshold is the same calculation towards the rear. A low number means either the centre of gravity is too high or too far back. Moving the battery is usually the cheapest fix.
We want to know if raising the lift mid-drive is safe.
Put in how much weight the lift moves and how far it rises. The tool shows how far that drags the whole robot's balance point up, and every threshold falls with it. That is why a lift is safest driven low.
Deciding whether to add weight low down.
Weight cancels out of the thresholds entirely, so adding ballast does not make you harder to tip. What helps is putting mass low, which pulls the centre of gravity down. The tool shows the difference.
Push it until it goes over
The robot from the side, braking. The arrow is the force trying to tip it forward, and the balance point is the dot. At 100% it is exactly on the edge of lifting its back wheels — past that it goes over. Raise the lift in the inputs above and watch how much sooner it happens.
How this is calculated
A robot pivots about the wheels it would go over. Accelerating forwards throws the weight backwards, and the robot lifts its front wheels when the tipping moment beats the restoring one:
tips when a > g × (distance from CG to those wheels) ÷ (CG height)The surprise in that expression is what is missing. Weight appears on both sides and cancels out completely. A heavier robot is no more or less likely to tip. Only the shape matters: how far the balance point sits from the pivot, and how high it sits.
Which is why a raised lift changes everything
Total weight does not affect the threshold, but it does decide where the CG sits. Lifting part of the robot drags the whole-robot balance point up with it, in proportion to that part's share of the mass:
CG rise = (weight that moves × how far it rises) ÷ total weightWith your numbers
Four pounds rising twenty inches on a fifteen pound robot lifts the CG by over five inches. Since every threshold divides by CG height, that can cut your stability margin in half without a single part changing.
This is why robots tip while carrying a load and not while empty, and why the honest number to design against is the one with the lift up. That is the case shown in the results.
The question that actually matters
A threshold means nothing until you know whether you can reach it. The most acceleration the floor can ever hand you is set by grip:
maximum acceleration = grip × gSo the two possibilities are:
- Grip is lower than the threshold. The wheels break loose before the robot rotates. It cannot tip under its own power. It just spins its wheels. This is the usual situation, and it is why most VEX robots never wheelie no matter how hard they are driven.
- Grip is higher than the threshold. The robot rotates before the wheels slip. It can and will tip under its own acceleration, and it will do so the first time a driver slams the sticks.
Note the uncomfortable implication: improving your grip moves you towards tipping. Fresh traction wheels on a tall robot can make it tip in ways the same robot on worn omnis never did.
Where the numbers do not save you
None of this covers being hit. Another robot slamming into yours applies a force well above the floor, at a height where it has real leverage, and no amount of grip analysis predicts that. Nor does it cover a lift raised mid-match, which moves the CG upward and makes every threshold on this page worse, so recalculate with the arm up if that is how you drive.
Ramp angle
The same geometry gives the steepest slope the robot can sit on before it topples, which is simply the angle whose tangent is that distance over that height. It is a convenient thing to sanity-check against, because you can tilt the real robot and see whether it agrees.
Sources & assumptions
No VEX-specific data is used. The thresholds are rigid-body statics and follow from your own measurements.
The friction coefficient is estimated, since no VEX figure exists, and it only affects the question of whether a threshold is reachable, not the thresholds themselves.
Assumes a rigid robot on flat ground with no suspension, weight shared evenly, and no external contact. It models a steady acceleration, not an impact: a sharp jolt can tip a robot that this page calls safe.
Save this run, and compare
Keeps what is on screen so you can change something and see both sides of the change. Saved in this browser only, never uploaded.
Save this as evidence
Collects what you entered, what came out, how it was worked out, and anything the tool flagged, with a timestamp and a version so someone else can reproduce it.
This is evidence, not a notebook entry. It deliberately does not write your problem statement, your reasoning, or your conclusion, because under RECF rules an Engineering Notebook has to be the students' own work and no tool may generate or organise its content. Take the numbers, decide what matters, and write it yourself.