Part I — VEX IQ Fundamentals · Chapter 9
PTOs
One motor, two mechanisms, switching between them instead of running both at once.
A PTO (Power Take Off) lets one motor drive two different mechanisms, switching between them instead of running both at once.
Build the robot without a PTO first. A PTO doesn't fix a slow or unreliable robot, it makes an already-working robot faster. Add it last, after your drivetrain and mechanisms already score reliably on their own.
Four common IQ PTO types, pick based on space and speed. Differential: two output directions, fast switching, no pneumatics needed, but heavy and takes up a lot of space. Slide: two output directions, swift switching, but needs pneumatics and takes up a lot of space. Gravity: no pneumatics, easy to build, but only one output direction and switches slower. Latch: two output directions, easy to build, but switches slower and takes up more space.
Friction is the real enemy of a good PTO, differentials most of all. A PTO only works if the disengaged side actually disengages, any extra friction in the gear train drags the "off" mechanism along for the ride and wastes power. Differentials are the worst offender, every gear mesh inside has to be nearly perfect or the whole thing binds. Budget real tuning time, this isn't a build-it-once-and-forget mechanism.
A PTO doesn't create power, it reallocates it. Two mechanisms rarely need full motor count at the same instant. A permanent 2/2 split wastes power on both ends. A PTO sends all of it to whichever mechanism is active.
Motor-sharing between intake and lift meant 4 full motors on intake, then 4 full motors on lift, instead of a fixed 2/2 split. Scoring got faster on both ends.
The highest-value trade is drivetrain vs. mechanism. Driving and scoring rarely happen at the exact same instant, so borrowing drivetrain motors during scoring, and mechanism motors during driving, is close to free power.
4-motor drivetrain when the lift is down, 2-motor drivetrain plus 2 lift motors when raising the beam lift to score. Field speed nearly doubled. That's what got us max-score runs.
A PTO can expand mid-season when another function needs the same fix. Rapid Relay's first PTO split one motor bank across three mechanisms, intake, outtake, and catapult. Partway through the season the drivetrain needed more power too, so we folded it into the same shared system, four mechanisms combined instead of three. More complexity, but it unlocked speed we couldn't get otherwise.
Remember why you're doing this. A PTO doesn't rescue a struggling robot, it takes a robot that already works and makes it faster. If your base robot isn't reliable yet, fix that first, a PTO bolted onto a shaky robot just gives you a shaky robot with extra friction.
One-line takeaway
A PTO is a late-season upgrade, not a starting design. Build reliable first, add speed second.