Mobility
Moving yourself and scoring elements around quickly and precisely.
Every FRC robot is a controlled power system.
All mechanisms follow this flow chart:
Motor → Transmission → Output
The quality of your design depends on how well you control:
Torque (force)
Speed
Efficiency
Reliability
All transmission systems fundamentally trade speed for torque or vice versa.
Motors
Motors define the raw performance limits of the system.
High speed → low torque
High torque → low speed
This relationship is fixed by physics. You cannot get both at the same time amd must transform it mechanically.
Motor Curves
A motor curve is a graph that shows Speed (RPM) on the x-axis and Torque (force) on the y-axis. It describes how fast a motor spins at different loads.
Every motor curve is defined by two endpoints.
1. Stall torque
Maximum torque
Speed = 0 (not moving)
2. Free speed (no-load speed)
Maximum speed
Torque = 0 (no load)
All real operating points lie between these two.
Power Transmission
Power transmission systems do three jobs:
Relocate power (motor isn’t always at the mechanism)
Modify torque and speed
Maintain synchronization between parts
The three primary systems are used in FRC:
Gears
Belts (pulleys)
Chain (sprockets)
Gears
Gears transfer motion through direct tooth engagement, resulting in very little slip, high efficiency, and precise motion. When two gears mesh, they rotate in opposite directions, and teeth enforce a fixed velocity ratio.
Gear Ratios
Example:
12T → 84T = 7:1
Torque ×7
Speed ÷7
Multiple gear stages multiply:
3:1 × 4:1 = 12:1 total
This is how gearboxes achieve large reductions in compact space.
Design implications
Larger ratios = more torque but slower response
More stages = more friction and backlash
Gear spacing must be precise
The Powered Elevator uses a set of gears to transmit power
Pulleys & Belts
Belts use a flexible loop to transfer motion between pulleys. Unlike gears, shafts can be far apart and rotation stays in the same direction. Ratio is determined by pulley tooth count the same as gears. There is also compliance in the system.
Advantages:
Lightweight
Quiet
Absorb shock (protects motors)
Limitations:
Teeth can skip under high load
Lower maximum torque than chain
Where belts are best used
Intakes and conveyors
Systems where weight matters
Mechanisms where you would rather the motor slip rather than stall
The 2026 kitbot uses pulleys and belts to transfer power from the motor to the launcher and intake.
Sprockets & Chain
Chain systems use rigid links engaging with sprockets.
Advantages:
Chain has very little slip (like gears) and can span long distances (like belts).
Sprockets will rotate in the same direction.
Chain also has a high load capacity.
Limitations:
Chain physically elongates over time, requiring tensioning.
For Competition Robotics AndyMark recommends #25 Chain Roller Chain for lighter duty applications or #35 Roller Chain for heavier duty applications. Although this industrial roller chain may look similar to bicycle chain, the pitch - or distance between the pins - is different and likely will not be compatible with bicycle chain links and sprockets.
Chain can be attached and broken using a few different types of tools. AndyMark recommends the “Dark Soul” chain break tool for #25 chain and the ARC tool for #35 chain. These tools push in and out individual link pins for a clean break and reattachment point.
Connecting Links: Standard connection links pin two ends of chain together to make a loop. Each end of the chain needs to end with a “narrow” link section. The link is held together by a clip that sits in a groove on the two connector pins.
Half Links: Also called an Offset Link, is for applications where one more link is too long, and one fewer link is too short. A half link connects a “narrow” link section to a “wide” link section. The link is secured with a cotter pin.
1.5 Links: This connects to two “narrow” link sections using two connecting links, but adds an additional half link section to the overall length. Use this to eliminate the potential failure point of a cotter pin connection.
Chain Attachment Links: These are useful links to add mounting points to your chain. Add the K-link to your chain path and bolt or rivet the link to the element you want to move to create an elevator or conveyor.
Sport Gearboxes
A sport gearbox is a multi-stage gear reduction system packaged for easy use. The Sport Gearbox is a competition tested high-performance line of planetary gearboxes from AndyMark and BaneBots that iterates on years of previous planetary gearboxes used in FIRST Robotics Competition. It has been optimized for strength and volume with durable steel gears and a single piece aluminum housing, ensuring that there is no possibility for misalignment of the stages.
It includes:
Motor interface
Internal gear train
Output shaft
This allows large reductions in a small space and high torque output with a manageable size.
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