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What is Overdrive?
To start off, servos need a pulse train like shown to the right.
This is known as the frame rate. The frame repeats its self, and is dependant on the transmitter/receiver used.
If you send the pulses too slow it will jitter away very badly, not hold its position very well, and be very slow to move.
So why dont we send frames as fast as we can? Two reasons, first, backward compatibility.
This means you can plug just about any servo into your receiver you wish, and it will just work.
Now, the second, and major reason, multiple channels. A servo requires a pulse in the general range of 1ms to 2ms, to command
it to its position. To be compatible with existing systems, 98% of transmiters transmit the pulses for each channel, one after
another. (see pic to the right)
We wont go further into detail here, but we will get back on point.
When a servo receives its command pulse, the servo motor turns on right afterwards for a brief amount of time, about 1ms.
Then waits for another command, then turns its motor on once again. So as you can guess, the motor is only being powered about
1ms out of every frame.
Now this is where the Overdrive technology comes into play!
Overdrive will send out frames every 4ms, thats a 250Hz update rate. Allowing you to take full advantage of digital servos!
The Overdrive, while driving your servos at 250Hz, will get its updates from your receiver at the lower frame rates.
Now your servos will have up to 5X more holding power, and get to their command positions faster!
How is it faster?
Simple, when your reciever sends the command to go to position, the servo motor is only on for about 1ms, then waits,
not moving, just waiting for the next frame to arrive. But with the Overdrive, the servo is commanded up to 5 more times instead of just
waiting for the receiver to send its next frame!
As you can see in this picture below, the overdrive continues to put out steady frames while the receiver is sending frames at a low frame rate.
If you would like to see some typical frame rates, check out this page: Frame Rates
High Speed Camera, 250Hz - 4ms Frame
Normal Speed Digital Servos
Overdrive Beta on right servo
Note: Overdrive technology is NOT compatible with Analog servos! Overdriving will destroy an analog servo!
Typical frames repeat every 12ms to 25ms.
The frame rate is dependant on the transmitter and receiver used.
Note: DX7SE Transmitter has 11ms frames,
this is a 90Hz update rate.
If you would like to see some typical frame rates, check out this page: Frame Rates
If you transmit 7 channels, and each servo is 2ms long, then 2ms X 7 channels = 14ms, and that doesnt include the space between the channels either.
