HiPowered Servos using Simple H from Robotpower and hacked hitec servo

HI -

After a lot of experiments, I’ve had some success with my auto throttle – I have a original 747 200 quadrant, and therefore needed a heavier motor/servo to run the AT – basically, Ive used the Phidgets4motor servo, a hacked Hitec Servomotor and a Simple H amplifier. Using this, I can run a dc motor upto 24V/25A, controlled by FS2Phidgets

Here’s what I needed:
One Phidgets 4 motor servo card
One hitec servomotor (does not matter which one, but I’ve used the HS815BB (what I really needed was the circuit and pot inside)
One Robotpower Simple H amplifier - http://www.robotpower.com/products/simple-h_info.html – great little device
One 24V DC motor - (V and RPM depends on your linkage/gear/system)

My main problem was that I needed a heavier motor to run my OEM throttles – the available options (as described on the forums) were to weak to do this – plus (most importantly), I needed to use FS2Phidhets to get the servo to talk to FS, and for calibration -

I knew that the system works fine with the 815BB, I’ve tested it running with FS, and it tracks the AT correctly (as posted by many simmers) – the Hitec consists of a circuit board, a pot connected to the final output shaft, gears and a small dc motor – the leads from the Phidgets4motor servo and the onboard pot are connected internally to the Hitec circuit board. What I really needed to do was to use the output to the hitec motor and boost it to a higher voltage for the larger motor, and set the pot remote on the throttle lever for position.

I cut the leads to the hitec motor and connected them to the input on the Simple H – the H sees this output as a variable voltage signal, and will boost it to any output (24V, 25A max) depending on the power you give to the Simple H independently.

Next, I cut the leads to the pot, and set it remote on the #1 throttle lever, to track the position. The attached diagram shows the connections -you can also download it here:
http://www.farrokhchothia.com/simplehservo/

Configuration: (how I did it, each setup would be different) -

Remove the motor from the gearbox assembly, keep it next to you @ the FS2P screen
Attach pot to Throttle lever (say #1)
Wire up the cards as per the diagram, and enable the Simple H with +5v
Set the aircraft in-flight, say at FL10 – speed 250 – with AT on
Set a max climb thrust, say 4000fpm @300Knots
Verify that the onscreen FS throttles are at the max position, and the FS value (0 > +16384) is in the upper end values (use offset 089A and not 088C!)
Note that the motor is turning
Place throttle lever just 1/2 inch shy of the forward stop
Adjust the Servo Range of Travel slider for the upper limit till the motor stops turning, ie, the error signal is null
Next, set the aircraft into a decent where the on screen levers are at idle, and FS value is close to 0
Note the motor turning in the opposite direction
Set the throttle levers to 1/2 inch shy of the idle stop end
Adjust the Servo Range of Travel slider for the lower limit till the motor stops turning, ie, error signal is null
You have your Servo Range
While re attaching the motor to the linkage, set max thrust in FS and place the levers to the forward position (1/2 inch shy, or till the motor stops turning) and then attach the motor to the linkage in that position – (you coud do this with FS at full idle as well) as long as the pot to throttle lever position remains fixed, this will hold -
If needed, for safety, you can fix limit switches at either end of the throttle lever travel to cut out the motor, if for some reason there’s a spike somewhere.

Using the Simple H frees you to use higher voltage motors, right upto 24V/20A continuous, and lets you use FS2P to control – in effect FS2P sees this rig as a Hitec Servo -

Cheers

Farrokh