Servo range problem


I encounter a little problem playing with my arduino board. I am just trying to have one servo going in two positions. The servo is a Futaba s3151 (doc here: The Arduino Board is powered by USB, and the servo by a Laboratory Power Suply in 5V, 200mA max. Grounds are connected.

It is working perfectly fine in the mid range (30° to 160° aprox.), or (775ms pulse to 2177ms pulse) But outside this range, the servo is de-activated.

I switched to the Servo -> Sweep example to eliminate software problem. The servo is sweeping from 30° to 160°, the a littel pause de-activated, the sweeping from 160 to 30, the a littel pause de-activated .....

I change to a small 9g servo, and it is working fine the whole range.

Does anyone allready had a problem like this?

Thanks you,


Per the below specs, the servo might not have a full 180 deg operating range. Your 5v 200ma max power supply will probably not be adequate for the servo to do much.

Control System: +Pulse Width Control 1520usec Neutral Required Pulse: 3-5 Volt Peak to Peak Square Wave Operating Voltage: 4.8-6.0 Volts Operating Temperature Range: -20 to +60 Degree C Operating Speed (4.8V): 0.21sec/60 degrees at no load Operating Speed (6.0V): 0.19sec/60 degrees at no load Stall Torque (4.8V): 43 oz/in. ( Stall Torque (6.0V): 56 oz/in. ( Operating Angle: 45 Deg. one side pulse traveling 400usec 360 Modifiable: Yes Direction: Counter Clockwise/Pulse Traveling 1520-1900usec Current Drain (4.8V): 7.2mA/idle Current Drain (6.0V): 8mA/idle Motor Type: 3 Pole Ferrite Potentiometer Drive: Indirect Drive Bearing Type: Dual Ball Bearing Gear Type: All Nylon Gears Connector Wire Length: 12" Dimensions: 1.6" x 0.8"x 1.4" (41 x 20 x 36mm) Weight: 1.5oz. (43g)

Something more like 0.5 to 1.5A might be better for that servo, given its high torque.

You can calculate theoretical load currents from the other specifications for a DC motor (geared or not). current x voltage = power, torque x angular velocity = power.

Thus current = torque x angular velocity / voltage.

Here torque at 6V = 56 = 0.41 Nm - the max torque figure, roughly represents stall or near-stall condition angular velocity at 6V = 5.5 rad/s (0.19s for 60 degrees). Therefore theoretical current at that torque is 0.41 x 5.5 / 6.0 = 0.38A not allowing for any electrical or frictional losses. 1A is a good guestimate I think.