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AEO-RC S1 Servo Tester w/ Gyro Sensor

AEO-RC S1 Servo Tester w/ Gyro Sensor
Item# 88E-AEDS400-S1-ServoTester

This item is currently out of stock!

AEORC's S1 servo tester is specifically designed to accurately measure the servo speed and helps to understand the overall performance. AEORC's S1 servo tester is the first integrated servo tester in the market which allows you to measure speed, duty cycle, travel linear & range also receiver output signal and frequency.

Input voltage: 8~12V (2S lipo or 9V 2A DC power supply)
Output voltage: 5V
Output current: 1A
Accuracy: 1us +/- 10%
Weight: 21g
Size: 69x33x11mm
Operating temperature: -10~50°C
1 x Servo tester
1 x Gyro sensor
1 x voltage regulated multi-functional servo extension wire
Customer Review (jj604 from RCGroups.com)

The AEORC S1 Dr Servo is a tiny box using the same packaging as the clever kV meter.  It consists of a servo driver and an input for an accelerometer that you attach to the servo’s output disk/arm. That input measures the pulse position so is also used to test receiver servo outputs. It also requires an external 8-12V DC supply. They suggest a 2S LiPo, but after using it I would recommend a 3S. The lower voltage just does not seem to have quite enough headroom to supply the 5V to drive the servo at higher currents. Most folks will probably be using the BEC from their ESC to drive the servos in any case – see the three way cable description later. 

The inside of the accelerometer is just a sealed unit with a part number that I could not raise on the internet with an external diode and resistor. I suspect it is the same unit used in single axis piezo helicopter gyros. AEORC call the device a ”gyro” and I’ll do the same for simplicity. The only control is one of those 4-way joysticks with a centre push that you find on every compact digital camera. Long push to move between the 4 screens; up/down/sideways to select a value if appropriate; short push to turn the backlight on and off or start a test. In my view it would have been more logical to make the short push for menu change and long push for backlight/start. The backlight keeps going on and off when you don’t want it to and on the other hand you have to dwell on a screen to change to the next one. This results in an unwanted test starting sometimes. No big deal, and doesn’t detract from the functionality - just an irritation.

In use, you just plug in the external battery, connect the servo and gyro and stick the gyro to the servo output disk or arm with foam tape. Alternatively you can use the gyro input to test transmitter stick range and centring. There are 4 functions on the tester:

1. Display of receiver output signal pulse width to the servo channels in thousandths of mS with a default neutral of 1.500mS (handy to very conveniently check how consistent the range and neutral your transmitter channels are). A servo-plug to servo-plug cable is supplied for this and you connect the gyro channel into each receiver output in turn. The supplied connectors are Futaba style and the ridges have to be cut off to allow the plugs to line up along the edge of the S1. Minor, but irritating. This menu must also be used to set the signal pulse width to give a 60 degree rotation (since the pulse length to do that may vary from servo to servo).

2. A cycle test that logs the number of repeating input cycles together with the number of output cycles recorded by the gyro (good for testing suspect servos). It reads up to 9999999999 cycles which for a 0.1sec servo would be a total test time of about 31 years if I have done the math correctly!

3. Measurement of servo travel linearity, which is really no more than setting up 2 or 3 servos side by side and comparing them as they are driven at the same time.

4. Measurement of servo speed, which is the uniquely useful and important function of this gadget.

To measure servo speed, you first need to tell the S1 what pulse width gives 60 degrees rotation. It’s remarkably simple to position the servo over the protractor they have printed in the manual and use the joystick to move the servo from the neutral position. When the holes in the horn line up at 60 degrees, you just read off the pulse width, subtract the neutral value and adjust it on the measurement screen with the joystick. It turned out to be much easier and more consistent than I expected. My guess is it is accurate to a couple of degrees if you are careful to align your eye with the shaft of the servo on the baseline. Obsessive can set up a more accurate rig to measure rotation precisely. Then you just push the button, the servos cycles a couple of times and the time to move 60 degrees is displayed in 1/100th’s of mS (more on accuracy later). You can do 10 readings in as many seconds. If the servo doesn’t respond, a long push upwards on the joystick reverses the signal – neat.

This is the simple way, and uses an internal regulator in the S1 to provide 5V at a max of 1 Amp to the servo. If you want to measure at the “standard” 4.8V then use any of the servo connectors on the supplied three-way splitter lead which then plugs into the S1. See attached picture TestSetup.jpg. The lead contains a 220µF capacitor to provide some reserve for peak current draw and a forward connected series Schottky diode in the main lead which drops the 5V to almost exactly 4.8V and protects the S1 from external voltages from the branch leads at the same time. Very simple and clever. If you want to measure at a different voltage, say 6V or use your ESC’s BEC, then just plug an external supply into one of the three servo connectors.

Results for AEORC S1 Dr Servo

Initially, no servo worked for me without an external battery supply. Changing the 2S 1000mAh battery supply to a 9V 2.5A power supply made no difference. I measured 0.46V at the servo supply connector. AEORC were helpful and responsive but in the end I discovered the Schottky diode in the harness was assembled in reverse (it’s very hard to spot the band on the diode). Once fixed, everything worked as expected. Be worth checking if you have the same problem.
The sensor weighs 9.5g so can be used on quite small servos. There is no simple way to calculate what the inertial load of the sensor is on the servo of course so it isn’t quite “unloaded”. Here are a few sample results averaged over 6 cycles.
Using a stabilized Lab 2.5A supply:

See Table 1

Using a 40A ESC with 4S 5000mAh LiPo: BEC voltage measured at 5.16V for same servos as above.


See Table 2

Using without any external supply gives approx 4.85V at the servo.
Results without external supply for 3x Bluebird BMS-375DMG – 11.4g. 
Claimed speed at 4.8V = 130mS. Three identical out-of-the-box, unused servos.


See Table 3

For fun: Some old servos of late 70’s vintage


See Table 4

The Orbits were the ultimate small servo at the time, have served me well, and cost a fortune. They still hold up not too badly 30 years later! The Charlie’s (Cannon in kit form) were the smallest servo available and a feat in their day – but look at the response speed.



Like many digital display devices this one reads out to unrealistic precision. The specs say accuracy is 1µS +/- 10%. “10% of what?” is the issue. Times in µS are reasonable for measurement of signal pulse width but not servo movement. There is no information on precisely how this gadget works but I assume it just measures the time between start of acceleration and end of deceleration. There is going to be some imprecision about this no matter how good the timing circuits are. I would suggest a basic accuracy of perhaps 1 mS for servo traverse is both reasonable and entirely adequate, not the 10 µS that is displayed. I found variations over 10 cycles of less than 3 mS with a new Hitec servo on a 6V supply so I’m assuming the S1 itself is probably good for at least 1 mS accuracy and anything more is servo variation. In other words I think what the specs mean is the READOUT is good to 1 microsecond not the accuracy. In any event this is more than adequate. It’s pretty clear from the numbers above that the variation between cycles and between individual servos of the same type is significant. In general the better the quality of the servo the less variation. Those old 70’s Charlies servos I built from a kit were a wonder in their day but a HobbyKing $2.99 special leaves them for dead!

I did quite a number of tests on different servos using a variety of power supplies and I came to the following conclusions:

This is a uniquely useful device. There are other servos testers of varying complexity but all the ones I have seen are really just servo drivers. I am unaware of any other low cost device that actually measures the servo cycle speed. Be interested if anyone knows of another.

It is low cost and simple to use. Once you get the hang of it you can test a bunch of servos in a few minutes. I found surprising variation between “identical” servos and also between specified and actual performance – particularly at the low-cost generic end of the spectrum.

I’m not into helis but I know there is a great need for speed in the tail rotor servo in particular. This would seem to be a good investment there.

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