Choosing a Motor

Gearboxes

There are two kinds of gearboxes: spur gearboxes, and planetary (also known as orbital) gearboxes. Their inner structure and difference is discussed in detail in Gearbox Internals section. For new teams, it suffices to know that planetary gearboxes much more reliable, but may be slightly more expensive. Spur gearboxes can strip under shock loads (for example, when your robot hits a wall), requiring you to replace the gearbox. For this reason, it is advised to use planetary gearboxs, especially in high-load use cases such as drivetrains.

Planetary Gearboxes

Standard planetary gearboxes include AndyMark NeveRest Orbital motors, REV 20:1 Planetary motor, and goBILDA’s 5202/5203/5204 Series Yellow Jacket Motors.

Any of these “standard” gearboxes are more robust than spur gearboxes. Like the spur gearboxes, the gearboxes from different vendors, while not interchangeable, are very comparable in terms of robustness. Once again, the main thing to consider here is your desired reduction, your desired motor connections, and your desired output shaft type.

  • goBILDA Yellow Jacket has the most varied selection of gearbox ratios with too many to list here, but utilize the rather uncommon 3.5mm Bullet connection for power. The output shaft is a 8mm REX (7mm hex rounded to 8 mm) or 6mm D-shaft.

  • REV HD Hex Motor with UltraPlanetary Gearbox - The UltraPlanetary is a customizable planetary gearbox that is designed for FTC. The three gearbox options are 3:1, 4:1, and 5:1, and can be mix & matched to create a custom ratio. It is possible to use from one to three gearboxes for a minimum ratio of 3:1 and a maximum of 125:1. The motor uses the same connections (JST VH) as the REV Expansion and Control Hub for power, which means no adapter cables are necessary.

    Note

    While REV lists the UltraPlanetary stages as 3:1, 4:1, and 5:1, their actual gear ratios are slightly different. Consult the REV UltraPlanetary User’s Manual for the exact gear ratios .

    The UltraPlanetary was intended to give teams maximum customization without the typical limiting factor - high cost. The total cost for the three stage gearbox and motor is exceptionally good value for a customizable motor. In addition, the UltraPlanetary has a female 5mm hex output shaft which allows teams to customize the shaft length.

    Tip

    goBILDA sells a special output adapter and motor mount that allows easily using the UltraPlanetary with the goBILDA system.

  • AndyMark NeveRest Orbital motors come in four ratios, 1:1, 3.7:1, 19.2:1, 50.9:1, and 263.7:1. The output shaft is a 6mm D-shaft, and the motors have inbuilt cables with Anderson PowerPole or JST VH connectors to connect to power.

  • AndyMark NeveRest Hex motors come in five ratios, 1:1, 3.7:1, 13.7:1, 19.2:1, 50.9:1, and 263.7:1. The output shaft is a 3/8 inch hex shaft, and the motors have JST VH connectors on the motors to connect to power cables.

Spur Gearboxes

Danger

Spur gearboxes are NOT recommended due to their shorter lifespan and lower mechanical resilience compared to planetary gearboxes. If you are purchasing new motors, it is highly suggested to purchase planetary gearbox motors instead. Care should be taken to not put load on the output shaft of a spur gearbox. In particular, spur gear motors should NOT be used in high load applications, such as a drivetrain.

Motors with spur gearboxes include AndyMark NeveRest Classic motors (in 40:1 and 60:1 ratios), the REV HD Hex 40:1 Spur motor, and the discontinued goBILDA 5201 Series Yellow Jacket Spur Gear Motors. All of them offer similar performance and reliability, so your choice is primarily dictated by the convenience of mounting and connecting to the rest of your design (e.g., if you use REV kit, you should probably choose REV HD Hex motor, as it uses the same 5mm hex shaft as the rest of REV system).

Choosing The Right Gearbox

For regular use, any of the planetary gearboxes will fit your needs. Planetary gearboxes are just a tiny bit more expensive, but boast better backlash and efficiency, higher load capacity, and better capacity for shock loads than spur gearboxes. The tradeoffs, cost and mechanical noise, are almost never a factor.

Tip

Because both gearbox types are so similar in price for similar ratios, we generally recommend the use of a planetary over a spur gearbox.

If you already own spur gearboxes, try to use them in lower-load situations, and use planetary motors on your drivetrain and high-load mechanisms.

For small reductions, it may be more economical to choose a motor you already own and build an external reduction using gears, chain, or belts. It should again come down to your desired output shaft, desired gear ratio, and for the UltraPlanetary, whether you want the ability to swap parts out on the fly.