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Alternate Controller
Has anyone come up with another way to control the vex? I want to control it with my laptop instead of having to use the remote control. This way the vex can get into autonomous development. The people of vex should make some kind of usb connection to the microcontroller. If someone has an oscilloscope or a logic analyzer you could test the signal comming out of the back of the remote control. I wish I had a scope at home... Anyway, if someone does analyze the signals and makes up some kind of chart post it here, it'd be very helpful.
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Re: Alternate Controller
i think it's pwm. 6, 1 for each channel, 1 to 2 ms pulses such that 1 ms is full reverse, 2ms is full forward and 1.5ms to stop. near as i can tell this is how cheaper rc controllers work.
not something your laptop will put out unless you want to try some low level stuff on the parallel port. might want to be running some sort of low latency OS on the laptop. of course, you can order a programming kit and write a little something to get the vex controller to listen on its serial port for instructions from your laptop. nice plain ascii human readable instructions at that. |
Re: Alternate Controller
I can see how this is a different topic, but you might want to look into this thread for some insight on some folks' work on making the controller programmable (before RadioShack releases the programming module, that is).
If someone can figure out the signals coming out of the tether port on the Vex controller, I could imagine them being replicated...but for programming autonomous behavior, the things they're talking about in that thread is right up your alley. |
Re: Alternate Controller
The cable that goes between the reciever and the vex controller is 4 conductor, so it isn't PWM. (PWM would require atleast 7 conductors (6 signals and one refrence)). I haven't really looked into it enough to know what its actually doing.
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Re: Alternate Controller
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True that it would require at least seven conductors to transfer 6 PWM signals, but that is only true if they are sent discretely. If they are sent via serial, it is quite possible that they could be sent over a four conductor cable. After reading this thread last night, I decided to look into the default code for VEX. Now understand, I am NOT a programming guru (yet), but I can figure a few things out by examination. It does look as though the signals sent from the Radio Controller to the micro controller are in fact PWMs. There appears to be no signals being returned to the Radio like there are on the FRC OI for things like LED's and Hex display. BTW, I just ordered the programming kit yesterday :D , it should be in this week, I hope, or early next week. I am also hoping the kit includes more info, like the other kits do. I'll post up what I received once it comes in. |
Re: Alternate Controller
i downloaded the default software posted at vexlabs this morning and scanned it over lunch and on the train home. it seems the master microcontroller posts pwm data to the user microcontroller every 18.5 ms. this is plenty of time for six one to two ms pulses. the fact that the variable names have the letters p, w and m only increases my confidence in my theory.
unfortunately the source code for the master controller is not posted so i can't claim absolute certitude. anyone interested can download http://www.vexlabs.com/docs/VexStartupCode.zip for now i'll be hiking to the vet for medicine for my hypertensive cat. ta-ta |
Re: Alternate Controller
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If I'm off base on this, sorry. As I said, I'm new to programming and still trying to reach Grasshopper level. Guru will take a while, 'till then, I deffer to those more knowledgeable. ;) |
Re: Alternate Controller
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I think the best solution for finding a way to use another controller would be to analyze the data being sent across the tether cable, not to disassemble the master code. My guess is that the tether uses a serial protocol, but I haven't looked at it. I'll check it out when I get home today and let you know what I find out. |
Re: Alternate Controller
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Your right, without the correct software tools, it is VERY DIFFICULT to decode them. I agree that the link between the remote and the micro controller is probably serial. That seems to make the most sense to me. I'll do a little more digging once I get the programming kit. UPS has it scheduled for delivery on the 14th. :D |
Re: Alternate Controller
i got tired of wondering and posted a query to the forum at vexlabs.com. the output of the r/c controller is indeed a pwm pulse train. abandon hope of controlling this with a pc. talk to the serial port instead.
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Re: Alternate Controller
I was looking at the transmitter over the weekend and found out the same thing. It may be possible to use a PIC or a basic stamp to take the serial output from a computer and use generate the appropriate PWM pulse for the desired analog value. The only thing that you would really need to find out is what the timing is for the different PWM outputs. The pinout for the tether port (for those of you that are interested) is from right to left if you are looking at the port on the transmitter is:
1 - Tether detect - used to enable/disable the radio transmitter 2 - Gnd 3 - PWM output 4 - +5v |
Re: Alternate Controller
thanks. can you tell us anything about the timing of the pulses?
seems like using pulsout and pause on a stamp would be kind of hairy given the millisecond resolution on the pause instruction, but i guess it depends on what the signal looks like. and if you're going to program a pic, you might as well program the one that's on the robot already. of course, that's 100 bills for the programmer. might not be such a far fetched idea, at that. |
Re: Alternate Controller
The answer I got from IFI regarding the timing of the signal is:
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This probably isn't going to be that hard to do. I'm going to use a PIC instead of the Basic Stamp (too slow). I'll look into this some more during the weekend, as I've got a lot going at work right now. |
Re: Alternate Controller
fowlerm, what say you scope the output of the controller and take a picture for us. might be worth a thousand or so words. maybe even more to my addled old brain.
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Re: Alternate Controller
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Also, there is a high-res picture here if you want higher detail. It's 1.8 megs, so dial-up users have been warned. |
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