|
|
Spockie-Tech
Site Admin
Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia
|
To get rid of the Interference, turn the Robot off - All Interference is now gone and nearly any radio works perfectly.. !
To effectively *cope* with the interference being unavoidably there is a different matter.
I havent tried a Spectrum System, but as far as Interference resistance goes, what I now believe makes the greatest improvement as far as Robot Use is concerned is a good error-detection and correction transmission system, not just the operating frequency
Remember, unlike other modellers, we are not operating at Extreme range. In fact, we arent even operating at "short range". Most R/C users would consider the <5 meters range we operate at practically Zero.
The challenge we have with robot use is dealing with extremely powerful bursts of radio noise very close to the receiving antenna from the wildly varying huge electrical currents in a robot, and having to somehow pickup a radio signal in amongst all that noise with a little fragment of an antenna gingerly poked out of our RF opaque armour.
We discovered that the American 72/75mhz radio' do improve things a lot over the Australian 36mhz ones.. - Probably because the amount of noise generated by our systems at the higher frequencies is less - It would be interesting for someone with a Spectrum Analyzer to do a noise-emitting-bands test on a robot and see where the noise is mainly generated to confirm this.
Given that the heavy currents are all down at 1-5Khz from the ESC's PWM output, and the arcing from the motors commutators, I would think that the higher frequencies should be less affected, but once you get up into the gigahertz bands, the difference in interference between 1ghz and 2.4ghz from motor noise might be less significant. Any radio gurus out there like to comment ?
As anyone who has suffered "the twitches" on a bot can tell you, its not a lack of range to start the 'bot moving, its *keeping* it moving through the noise once its motors have started.
Because of the way our receiver systems consider a transmission error to be a *bad*-thing and stop the robot immediately on an reception of an error.. what is needed is a system that ignores or corrects for errors in reception
without
significantly decreasing the safety of the system.
I used to be fairly against PCM radio systems as "decreasing the safety of the failsafe" since the receiver can continue to tell the robots controller that it has a good signal when in actual fact its currently receiving an invalid signal, and is waiting for the valid data stream to be resumed.
While this is strictly speaking true, having had a PCM radio system for a while now it doesnt seem to be the case in practice. I dont know the details of the PCM decoding scheme in the radio, but it has never falsely activated on me yet, or even twitched for that matter, so I suppose it has some system, where like a failsafe, it requires a certain number of valid signal in a row before the output activates.
This *might* just be a case of "I'm using it now, so it must be good" but I'm trying to be objective and not biased.
The main change that I have observed is that if a drive/weapon is running and you turn off the radio, it takes maybe 1/2 to 3/4 of a second longer to stop than a FM system that stops instantly. This isnt a big-deal safety wise - The main thing we want to avoid in a robot is accidental activation, particularly with instant-on weapon channels like pneumatics. PCM systems dont seem to be any more succeptible to this than straight FM or AM despite what I thought would be the case. if anything, they seem to be even better to me..
I've found that some Aero modellers dont like PCM, since a lot of them work on the theory that "half a signal (a noisy one) is better than none" when trying to bring your plane safely to the ground, or operating at long range.. but to our robots, a bad-signal is just as bad as no-signal and they will stop, so the modellers criteria dont really apply to our short range application.
So..
Altering the frequency the message is sent at may help to avoid some of interference bands, but having a system where the message's validity can be positively verified and acted upon or discarded accordingly seems to help more, so I'd be comparing the 9CAP and Specktrums transmission/error control systems more than their frequency.
*what a waffle.. been a while since I did one of those.. * _________________ Great minds discuss ideas. Average minds discuss events. Small minds discuss people
|
Sun Oct 30, 2005 4:26 pm |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|