Servo - December 2013

26 SERVO 12.2013

Stall Torque: 0.35 in-lbs for 11:1; 1.6 in-lbs for 50:1

Stall Current: 1.3A

Shaft: 3 mm diameter, 1.5 inches long

Weight: 0.99-1.02 oz

Cost: $22.94

Comments: The Finger Tech Robotics Silver Spark gearmotor is a very well made and durable drive motor option for the 1 lb class. It has been used in weapon focused 3 lb robots with a decent amount of success. With a wide range of ratios available ( 11.1, 22. 2, 33. 3, 50, 83. 3, 100, 200, 300, and 600:1), it is easy to find an option that fits your needs. These motors are also capable of handling much higher voltages than their competitors, and have been run as high as 22.2V (though >10V does decrease motor lifespan) in a combat application.

The long shaft gives you plenty of options for both wheels and supplemental shaft support, though the latter isn't often needed in the 1 lb class. These gearmotors have relatively large pitch gears and because of that they're far less prone to stripping under load.

This can often make the difference in a match and is one of the reasons they're very commonly found in 1 lb bots.

Kitbots 1,000 RPM Gearmotor

Dimensions:

.98-.03 inches diameter, 2. 14 inches long

Nominal Voltage:

12V

RPM: 930

Shaft: 4 mm diameter

Weight: 3 oz

Cost: $12-$24

Comments: There's very little in the way of dedicated gearmotors for the 3 lb class right now, and the Kitbots 1,000 RPM gearmotor is at the top of the pile. This somewhat generic looking gearmotor is effectively the off-the-shelf drive option for the 3 lb class.

There are other gearmotors out there, but they're often either difficult to attain, out of production, or unrealistically expensive.

Kitbots offers a "battle hardening" service that improves the durability of these gearmotors for $12, and it's worth either having them do it or following the instructions they have posted and doing it yourself.

This motor is prone to voltage spikes, so it is recommended that with some compatible ESC options you pair it with a 0.01 µF capacitor to protect the motor controller.

Gimson Robotics GR02

Dimensions: 1.6 inches square ( 40 mm),

3. 8 inches long

Nominal Voltage: 18V

RPM: 810 for 24:1;

542 for 36:1

Stall Torque:

106.8 in-lbs for 24:1; 160.2 in-lbs for 36:1

Stall Current: 61.6A

Shaft: 12 mm with flat

Weight: 1 lb

Cost: £ 29. 80

Comments: The GR02 is a gearmotor from the UK and is meant to function as a replacement for modified drill gearboxes in the popular 30 lb class. With the size and weight of this gearmotor, it is also suitable for the 12 lb class. The shaft on the GR02 can be troublesome for some builders, however, they offer a wheel hub solution that pairs with the 12 mm shaft which minimizes this issue. They're also shipping the gearboxes with an external bearing kit which can be used to help handle the shock loads that often come with an overhung wheel drive setup.

BotBitz GM36 19:1 Gearmotor

Dimensions: 1.42 inches diameter ( 36 mm), 3. 7 inches long

Nominal Voltage:

12V

RPM: 900

Stall Torque:

29. 7 in-lbs

Stall Current: 52A

Shaft: 8 mm with flat

Weight: 0.93 lbs

Cost: $40 AUD

Comments: The GM36 is the Australian solution to the same problem the GR02 addresses in the UK. Cordless drill gearboxes are nice and off-brand models can be quite cheap, but year to year the design, motors, and ratios can all change, making it difficult to get a reliable known motor. These gearmotors are also meant for the 30 lb weight class, though are certainly compact and