PWM from R/C receiver not driving controller?

I hope someone can help shine some light on this problem.. To put it simply: the RC receiver I have isn't working with my pwm motor controllers..
I have the Victor 884's from Innovation First (http://www.ifirobotics.com/victor-884-speed-controller-robots.shtml ), and the JR Quattro (http://robotcombat.com/marketplace_rc-quattro.html) r/c setup.
I've got a Brainstem (from acroname) that can drive servos, and the motor controllers via it's PWM port(s).
The R/C only works to drive the servos. When the R/C is connected to the motor controllers, the controllers just blink the LED's (which means no signal).
I also tried using IFI's 'pwm driver' which supposedly fixes pwm signals to their controllers when you're using non IFI equipment. It doesn't fix the problem for me, and I have no idea how it's supposed to work as I haven't found specs for it, and it's wrapped in a piece of heat shrink tubing..
From what I've read about PWM, the cycles are around 20ms, with 0-2ms peaks marking the beginning of each cycle/'frame'. Would the frequency of the pwm signal affect it's compatibility with other pwm devices?
If you have any pointers for me to get this working, please let me know.
Thanks, -Andrew
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Andrew,
About the only thing that springs to mind is check the polarity of the signal leads connecting the RX and the Motor controllers. If you have a DVM connect it across the signal lead (the motor controller can be connected or disconnected) and you will see a voltage across the signal and ground wires that varies with respect to the stick position on the TX. Do this at both the RX end and the other end of the cable incase it has a break in the middle.
Yes the PWM signal can have a variable frequency (usually between 19 and 22ms frame length) but I think what you are describing is the complete undecoded signal that contains the info for ALL the channels on the RX. Once decoded each servo output has a single pulse between about 1 and 2ms long repeating every 20ms, no start, stop or parity bits. Here is a link that describes the complete frame:
http://webpages.charter.net/rcfu/HelpsHints/RadioOps.html
And here's a link describing the operational theory behind a PWM contoller:
http://www.math.niu.edu/~behr/RC/pwm.html
Chris
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...

AFAIK, it's just two inverters in a row which helps to buffer and amplify the signal.
You might want to make sure that you have the + - and signal lines set correctly.
Not sure but I think it was JR that used to have + on the outside rail.
So if you flipped the connector by mistake, you could blow your servo.
DOC
Buy my junk! http://www3.sympatico.ca/doc/robotone/for-sale.html
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Well, I got everything working..
I took the RX/TX to school today and looked at everything on the (really nice tek) oscilloscope.
As it turns out, the JR Quattro (and probably other equipment) uses 3.3V pwm signals. The motor controllers apparently need 5V signals.
Thanks Doc for the mentioning inverter-inverter buffer, I wired up my own buffer circuit and got the PWM signal from 3.3V up to 5V.
When I used the 'signal driver' cables, the pwm signal was insanely noisy, which I guess is why they didnt work in the first place. They did however get the max signal voltage up to 5V.
So now I've got a nice $1.50 circuit that works, vs. two $15 circuit/cables that don't...
Thanks for the responses, -Andrew wil1 (at) umbc (dot) edu

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Was that 3.3v voltage swing measured in situ or open circuit?
Sounds more like you needed pull-up resistors on the signal lines rather than a 'signal booster'... R/C gear works fine on voltages from 4.5 to 6v. Try putting a 10K resistor between the + and signal wire and checking that on the scope at school, I'd put money on it then being able to swing from near 0 to 5v or the TTL levels it seems to need. The reason the RX didn't work is that its outputs are probably TTL open collector which need a pull up resistor to function properly, JR leave them out of the RX to conserve power and you have them in the servos and speedos so that only used outputs are drawing full power.
I'm assuming it uses TTL logic as that's what their FRC robotics controller uses, it doesn't say as such anywhere that I can see but the serial out put is TTL level so it's pretty safe to assume they used the same logic chips to buffer the PWM outputs.
Chris
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From my 4 year old FAQ of using the Victor controllers at http://www.teamdelta.com/products/v833faq.htm :
I hooked everything up properly and the the status LED just blinks. But when I plug an R/C servo into the same receiver channel it works fine. Is my Victor defective? No you just need an inline signal buffer. Many radio receivers cannot source enough current on the R/C signal line to drive the Victor so an extra part is needed. Experience has shown that most Futaba receivers require the buffer, Hitec do not. The inline buffer is available from me, from IFI, and possibly from your local hobby shop. Alternate names are "elevon amplifier" and "long cable filter." We also sell them, above.
I sell an intelligent signal amp that also performs two levels of noise filtering for $17.50 http://www.teamdelta.com/products/prod2b.htm
Dan
Andrew wrote:

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