Actuater

The robot employs 18 RC servomotors for actuator. I chose the servomotor because it is cheap and easy to control. I explain about the servomotors for Radio Control (RC) Model at this page.

SRM-1301

"SRM-1301" is the name of the servomotor. This model was the cheapest model I know. That is the biggest reason why I chose this model. Specification of this model is as shown below.

Maker	Sanwa
Speed	0.18 Sec./60 Deg.
Dimension	39.0*20.0*36.0(mm)
Torque	3.3 kg.cm
Weight	45 g
Market price	About 1300 yen (About $12 U.S.)

Control signal

This kind of servomotor is controlled with the signal as shown above. Stop angle of the servo is depending on how long the signal stay high level. The servos rotate about 60 degree, in case it is connected to RC receiver. But the model can actually rotate about 180 degree.

Characteristic of RC servomotor

The more difference between current direction of servo-horn and target direction exists, the more the servo consumes power and generates output torque. So the output torque of the servo can be controlled to some extent with regulating input current.

Figure shown below shows characteristic of RC servomotor. I putted a tip of a leg of the robot on a spring balance, and measured power consumption of servo 1. (Servo layout drawing)

Price

Many kind of RC servos are available and the price for them is depending on their performance. The cheapest class is about 3(kg.cm) at torque and 50(g) at weight. The smaller or faster or stronger servo costs several times expensive in general.