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mslezak

Futaba J Reciever Output Signal to ESC Voltage?

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I'm trying to use an electronic speed control for an RC device without connecting it to a receiver. The ESC is a Duratrax DTXM1030. It has a standard Futaba J connector which is supposed to connect to the RC receiver. I am using this in a car to control the power to an electrolysis unit (hydrogen and oxygen generator), so I don't want to hook up a receiver. Instead, I want to use a potentiometer to control the output current to the electrolysis cell (which will connect where the motor would normally connect).

Does anyone know what the signal is to the ESC from the receiver? On the internet, I have found that the Futaba J connector has Red+ Black- White=signal. The signal to the servos from the receiver=5V when 5V is powering the receiver. But I cannot locate the white signal output voltage and characteristics to the ESC.

My guess is that the signal is between 0V and 5V variable, but I'd like to be sure before hooking it up to avoid frying the ESC. Does anyone know for sure? Or can anyone measure it from their Futaba receiver? Thanks, I appreciate the help!

nocman43202-AT-yahoo.com

-Matt

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The signal is a square pulse with 0V and 5V levels. The high length of the pulse determines the stick position, 1ms being one extreme, 2ms the other extreme and 1.5ms the center. The time between two rising edges is 20ms.

I'll do some ASCII art:

Hope you understand ;)

Edit: The forum doesn't like extra spaces.... here's an image

post-6-1122586414_thumb.jpg

Edited by Kilrah

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Thank you very much!

I see what you are saying with the varied pulse width. It has to be properly timed then to get the desired output. Are you aware of a receiver simulator? What I mean is a device that plugs into the ESC with a potentiometer used to test the ESC. I just don't want to have to make a square wave generator that meets those criterea.

Also, are you positive that information is for the speed control? Futaba's site lists those criterea for driving the servo, which is why I ask.

I appreciate it!

-Matt

Edited by mslezak

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A receiver outputs the same signal regardless of what is connected to it! So basically everything that is designed to be connected to a R/C receiver expects that signal... What it does with it then depends of the device. Some ESC's require you for example to first put the stick at full throttle, then at idle or other sequences before activating the output (for security reasons).

Several R/C equipment manufacturer sell such things, but most of the time they offer more possibilities and thus are relatively expensive. I doubt it, but are you equipped with a PIC programmer? If yes I can send you some code I've made for a 12F675 that will do the job. You just need 2 parts, a pot and the PIC.

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Sure send me the code at nocman43202-AT-yahoo.com. I'm not sure where I'll find a PIC programmer, but I'm sure someone in town has one that I can track down.

So how do you set the pot and the PIC? Thanks, I appreciate all your help

Or if you could burn the PIC for me, I can you via PayPal for your time and shipping costs! That may be easier. I just googled the PIC programmer at $599!!!

Thanks again,

-Matt Slezak

Columbus, Ohio US

Edited by mslezak

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I appreciate your help!

Worst case scenario I'll burn the PIC at the school I'll be attending, I'm sure they have one in the engineering department!

Take care-Matt

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Hm, found it faster than I thought :)

So here it is, source, HEX and schematic. There are 2 channels, so if you want you can connect 2 pots and get 2 servo outputs.

Don't look too much at the code, it was quick-and-dirty programming I had to do for the same day, and due to be used only once :rolleyes:

Servoctl.zip

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Hey I bought a PIC programmer the HoodMicro http://www.k9spud.com/hoodmicro/ and it is on its way. It comes with a PIC12F629. Will this chip work with the code you sent me? I see they share a datasheet, pinout, but some additional features may be on the PIC12F675.

Thanks again for your help!

-Matt

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Nope, as the 12F629 doesn't have the A/D converter, which I use to sample the pots.

Just order the part as sample from Microchip :)

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Hey Kilrah, I owe you one. I burned the PIC yesterday and wired it up to a 100K pot today. I just had it connected to my car battery and it allows me to go between 0 and 20amps on my electrolysis unit. Did you design it for a smaller POT by chance? My range is limited to about 1/10 of the dial.

These PIC things are kinda cool; I'll have to read up on the programming stuff. Sounds like a whole bunch of controllers can be made with it. Again, thanks for your help!

Here's the schematic of what I hooked up with just one pot, for those that might need it.

post-6-1123389024_thumb.jpg

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Cool, nice to see it works :)

Any pot value can be used as it is used as a voltage divider. However, as the PIC's input resistance is not infinite it can degrade the linearity and range if the pot's resistance is too high (don't have the PIC's figures at hand now). I usually use 10k.

This range thing is strange though... I bet you should have an o'scope at hand, could you have a look at the output signal vs. pot position?

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Yes I have an oscilloscope on hand. I thought you were using this as a voltage divider, it is good to hear the hunch was correct! The ESC has an autoset function to set the brake and forward functions. It must have some predetermined range that can't be exceeded, as I tried to lower the neutral postion, but it won't let me go below a certain point, which is probably 1ms pulse width or whatever the reserved value is for the brake. Yes I calculated the various values comparing my 100K to a 10K as a voltage divider, and I see what you are saying - it should output the same voltage at the respective postions as the ratios will be the same. I may use the scope now or hold off - I have to make my way 1200 miles in a couple days via car!

Hey you should sell these things! My setup is an 8pin Dip holder with the pot wires connected to it for power, ground, and output signal. 24 gauge wires plug directly into the Futaba J connector from the ESC, which supplies the 5V BEC to power the device. The PIC holder could be easily epoxied on top of the pot to give a compact controller that just plugs into the Futaba J of the servo and ESC. I'm not sure who else would need it though.

If you ever put an electrolysis unit on your car, remember to use your PIC controller and an ESC to select the current! This is all part of a larger project, a vegetable oil car which runs on one tank, similar to the Elsbett system of Germany. This, however, uses hydrogen and oxygen, along with a proprietary fuel system, to enable transparent multi-viscosity fuel use. I will be moving to Houston and will attempt to use bunker fuel - the leftover product from crude oil refining. It costs about $0.90 per gallon in the U.S., and is largely used to power cargo boats. Diesel is averaging about $2.50 per gallon, and is expected to rise to $5.00 within 2 years. The project is still in the works, and I probably won't have a production ready vehicle for several years. But one day...

Thanks again for all your help! -Matt

Edited by mslezak

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