Hillhater said:
A further thought on this Hall throttle issue..
..this Turnigy servo tester has a "Auto" function (firmware ?) that will automatically run the ESC through the full speed range .. bypassing the potentiometer.
that would suggest that there is something else, other than the 0-5k pot, "on board" to control the output.
Maybe the Hall throttle is somehow using that firmware system ?? ( just random thoughts :? )
All the servo testers that I've seen recently have used a small microcontroller to generate the PPM signal for the servo. They often have two switchable options, one that uses the pot to control the waveform and one where the microcontroller just cycles through the allowable range.
The pot connections vary from one type of servo tester to another. I have one here that just uses two connections from the pot so is effectively just reading resistance - this wouldn't mate up with a Hall throttle well. I have an older one here (from my local model shop, with no brand name) that uses a 10K pot wired to give a 0 to +5V signal to the microcontroller. This may work with a Hall throttle, but the throttle range would probably be wrong, as the Hall throttles usually have about a 1.5 to 3.5V output voltage range when run from a 5V supply.
It's pretty easy to make an interface that will run from the 5V BEC supply and allow a Hall throttle to be used. A simple microcontroller, like the 8 pin Picaxe 08M, will run on +5V, draw negligible current, accept any analogue voltage input in the 0 to 5V range and output a PPM waveform that will directly drive an ESC. All that's needed is a bit of simple code (written in a form of BASIC) that will read the voltage from the throttle and use this to set the PPM signal. This is pretty easy stuff even for someone with no experience of writing code. The pseudo code would look something like this:
Mainloop:
Read ADC ; this read the voltage from the Hall throttle and converts it to a value between 0 and 1023
Subtract zero offset number ;the throttle isn't at 0V when closed, so the offset needs to be subtracted
Multiply or Divide by a factor to get the right SERVOPOS value ; this changes the raw voltage reading to a throttle value
Send throttle value number to SERVOPOS ; this tells a pin on the controller to generate a servo PPM pulse train
GOTO Mainloop ; this just loops the programme back to do the above sequence as fast as possible.
I've already done a board layout for a multipurpose throttle interface, using this controller (http://endless-sphere.com/forums/viewtopic.php?f=28&t=10908&start=105#p310462 ). The board is 1" square and just as three throttle wires going in and three wires going out to the ESC (assuming the ESC can provide +5V). The board also has a serial programming port so that the code can be loaded from the free Picaxe programming utility to the chip. To be honest there's no need for a circuit board for something this simple, you could just as easily stick the chip on a small bit of perf board to make the necessary connections, maybe potting the thing in a blob of resin or hot melt glue to make it watertight.
I've not got the time to make these things as a production article, but I may be able to sort the code out, test it and publish it so anyone else could make one fairly easily.
Jeremy