Choosing gears for an FTC robot usually means a lot of guessing, a pile of extra parts, and a few rebuilds. This free FTC gear ratio calculator lets your team plan the whole gear train first. Pick goBILDA or REV Robotics, drop real gears onto a channel, and instantly see which gears mesh, how fast each one spins, and your final gear ratio.
As a math teacher and FTC robotics coach, I built this tool so students can test ideas on screen before they cut, drill, or order anything. It is also a great way to show students that gear ratios are just fractions and multiplication in action.
FTC Gear Ratio Lab: goBILDA & REV
Pick your build system, drop gears onto the channel, and see which ones mesh, how fast each one spins, and your overall gear ratio before you build. Put gears inside the channel or outside on different layers, and stack two gears on one shaft to make a compound reduction.
Your gear train
Gears that mesh with the selected gear
Ratio finder
| Gear | Teeth | Layer | Position | Connected by | RPM | Direction | Ratio (motor : gear) |
|---|
How to Use the Gear Ratio Calculator
- Pick your brand and structure. Choose goBILDA (1120 U-Channel) or REV Robotics (45 × 15 mm C-Channel or 15 mm extrusion), then pick the channel length.
- Choose a mounting option. Use bearing holes only, the goBILDA 8 mm grid, or slots. In slot mode, the calculator snaps gears to the exact mesh distance for you.
- Add gears. Select a gear and click Add gear. Drag gears onto the holes, choose inside the channel or an outside layer, and use Duplicate to add the same gear again.
- Build compound gears. Click Add on same shaft to stack two gears on one shaft for a bigger reduction.
- Read your results. Set the motor, pick the output gear, and press Start to watch the gears turn. The calculator shows the overall ratio, output RPM, torque gain, and spin direction.
Features for FTC Robotics Teams
- Real gear catalogs: all goBILDA MOD 0.8 gears, plus REV plastic (MOD 0.75) and metal (MOD 0.8) gears.
- Inside or outside the channel: the calculator checks whether a gear actually fits between the channel walls.
- Ratio finder: type a target like 12 : 1 and get real one- or two-stage gear combinations, then click Build it.
- Mesh suggestions: click any gear to see every gear that meshes with it from an open hole.
- Instant warnings: colliding teeth, wrong center distances, locked gear loops, and mixed REV plastic and metal gears.
- Custom colors: color any gear to match your drawings or team notes.
Gear Ratio Basics in 60 Seconds
- Gear ratio = teeth on the driven gear ÷ teeth on the driving gear. A 15T gear driving a 45T gear gives 45 ÷ 15 = 3 : 1.
- Compound gears multiply. 3 : 1 followed by 4 : 1 gives 3 × 4 = 12 : 1.
- Speed and torque trade off. A 12 : 1 reduction turns 12 times slower with about 12 times more torque, before friction losses.
- Idler gears change direction, not the ratio. Every mesh flips the spin direction.
- goBILDA spacing: two gears mesh on bearing holes 24 mm apart when their teeth add up to 60, such as 20T + 40T or 30T + 30T, and 48 mm apart when they add up to 120, such as 40T + 80T.
- REV spacing: most REV gear pairs do not land exactly on the 16 mm hole spacing, so REV builds use slots to set the exact center distance.
Frequently Asked Questions
Is this FTC gear ratio calculator free?
Yes. It is completely free, with no login and nothing to download. It runs right in your browser.
Can I mix goBILDA and REV gears?
The calculator keeps each brand separate. goBILDA gears and REV metal gears are both MOD 0.8, but REV plastic gears are MOD 0.75 and cannot mesh with MOD 0.8 gears.
Is the calculator affiliated with goBILDA or REV Robotics?
No. It uses public specifications such as tooth counts and hole spacing, with simplified drawings made for this tool. Always double-check your design in CAD before you cut or order parts.
Try it with your team this week, and leave a comment with the gear ratio your robot ended up using! You can find robotics kits and parts in our STEM & Robotics shop.
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