ernest2

hi!
i have questions about radios before deciding what to buy.
first, what really is the difference between PCM and FM? i understand that PCM has a built in failsafe, but FM can be fittedwith a failsafe also.
second, when does the failsafe kicks in? does it start when the radio experience glitch? or just when in total loss of signal?
third, when an FM radio loses signal, this will activate the failsafe, but when it regains signal, can you still control the rudder?(if the failsafe is in the throttle servo)
fourth, in the PCM, is failsafe available to all the channels? and will control be regain once you regain signal?
i have tried turning my am radio on and off, like testing what will happen if i loss signal, and everytime i turned it back on, normal operations takes in, does it also apply to FM or PCM?
thanks a lot for your answers and comments, i want to buy a good radio, something i can use with a gasser and for scale boats (4 or 6 channels)
sorry,so many questions

ernest

piper_chuck

My Feedback: (12)

It's actually a bit inaccurate to compare FM and PCM. PCM uses FM for transmitting. You'd be more accurate comparing PPM and PCM. The "real" difference between PPM and PCM is not failsafe, that's just a feature that gets added to many PCM receivers. The difference is how the control signal is encoded on the radio waves.
The receiver decides when the failsafe kicks in. I haven't studied every option. The PCM receivers I've seen can be programmed to ignore small glitches and leave the servos where they are. After some amount of interferance or signal loss, the failsafe starts and the servos will go to the desired failsafe position.
Yes, and at this point the failsafe would also be reset.
I assume this is manufacturer specific. The PCM failsafes I'm familiar with can be programmed for all channels. And yes, once the receiver regains the signal, the failsafe gives back control.
This sounds normal. However, some receivers go crazy when they lose the signal.
Questions are what we're here for. Ask away!

ernest2

thanks for answering the questions piper, appreciate it.
now i have another, is the hitec agressor a good radio? it's the cheapest 3 channel i think, but lots of features. is it good for gas?
heres a link. http://www.hitecrcd.com/Radios/Menus/RadioHome.htm
thanks again

piper_chuck

My Feedback: (12)

It looks ok, however...

There are a couple things that would keep me from buying it. First, it looks like the 3rd channel isn't proportional. This means it can only send a servo all the way between endpoints. I run nitro boats and use the 3rd channel to control a needle valve. This isn't necessary for gas boats, so it could be ok.

The other thing to consider is if you ever think you will have more than one boat. If you do, a computer radio will allow you to run more than one from the same transmitter. When you are packing up stuff to go to the pond, this makes life much easier.

In reality, nearly any 2 or 3 channel radio will be ok for gas. FM is preferred since it reduces the possibility of interference from the engine's ignition system.

-Inverted-

The best budget 3 channel radio is the Hitec SRX, very good radio for the cost. I myself am currently using a Futaba 3PDF.

ernest2

SRX is also pretty nice, 130 @ tower. but at that price, i might just go with futaba 4channel exa 140@ tower, one extra channel for scale boat, yet computer and fm for gas boat.
whats the difference between 3 and 4 channel anyway? why is the price same or even even higher for 3 channels.

-Inverted-

You need a minimum of two channels, one for throttle; one for steering. Some radios have additional channels. You can do all sorts of things with your spare channels, I will soon be using mine to turn on a light kit. Boaters use additional channels to make tuning adjustments while the boat is out, as well as adjustable fins, etc. As long as you get your own servos, the SRX is only $99.

http://cgi.ebay.com/HiTec-AGGRESSOR-...QQcmdZViewItem

The answer is because the SRX is a very nice radio. The 4 channel your looking at is very basic.

LtDoc

ernest2,
Just a suggestion because of your original post. Since the radio is the most common thing between running any kind of boat, that's the place to spend 'quality' money (if that makes sense). The number of channels (after two or three) is just 'icing on the cake', not really necessary, but certainly nice to have. Never know when you might wanna add a hula-girl to your boat and the extra channel will make her 'shimmy' (not exactly the 'best' example in the world but I'll bet you get the meaning - lol).
Some very general things to think about is that 'AM' radios tend to be susceptible to interference more than 'FM' radios (always exceptions!). Lower frequency bands tend to be more prone to interference than higher bands, cuz there's usually more stuff near them (R/C, industrial, etc), also one of those things with exceptions. If all that isn't bad enough, then the 'secret' to having an interference free radio is painting it red, or magenta! Remember, that's a secret so don't tell anybody...
Have fun!
- 'Doc

ernest2

well i still have about a week to think about it.
i actually will need 3 channels minimum, i am currently making a patrol ship with 2 jet drives and needs the additional channel for the reverse bucket. extra channel will be extra only. the other use of the radio is for the gas boat, so i think for sure i will get an fm, pcm is too much.

ltdoc, what do you mean by lower and higher freq regarding interference? is 75mhz a higher freq? i currently have a 2ph 75mhz am radio. is seems ok, i even used it in my homie airboat.
and regarding your secret, is bright orange not included? i painted my new boat this color.

LtDoc

Should have paid more attention to where you were, no idea about band usage there. No, 75 Mhz isn't a low R/C band. 27 Mhz is, if it's available there. I wouldn't spend too much worry on high/low band, it was just something to think about depending on where you do your sailing. If I had the choice between Am or FM, I'd pick FM. Not all that much better, but sort of. After doing all the ballancing between 'best' this and 'best' that, and cost... sometimes cost wins - LOL.
- 'Doc

PS - (It isn't the color of the boat, the radio!)

rszanti

If monies not a big concern with the radio, you might take a look at the "Specktrum". It's a 2.4Ghz - 3 channel unit that's essentially glitch free (at least all reports to date claim this). $200 is the going price with receiver and three servos but I've seen it for $170 with the receiver and just two servos.

Richard

LtDoc

Richard,
If you're going to spend $200, why not get the 'Spektrum' DX6? Six channels, mixing, same range (more than most boaters will ever need). Don't know about the 'glich free' thingy, I have trouble believing that of any radio system. Haven't had one yet, but "Murphy" still lives in the same town I do - lol. Would I recommend a 'DX6' for most R/C people? Not really, unless you want the additional channels and small receiver size. Absolutely nothing wrong with it, I like mine. But, in most cases, you just probably don't need it.
- 'Doc

PS - WTH, buy it anyway!

ernest2

i would have love to get the spektrum radio, but its too much for me now.
i am currently considering the hitec srx3 channel or the towerhobbies 6xm (similar to futaba 6exas).
the hitec srx i think is a good radio for the price, but i also like the the 6 channels for extra features on scale boats, but the main problem is that it says 500yards range only, but is 500yards far enough? or i already need binaculars to see the boat
one thing, here, frequency doenst matter, whether its 27, 72 or 75mhz.
ernest

LtDoc

ernest,
If you can see a model boat at 500 yards you must be superman with telephoto vision - lol. Better bring a box to stand on. 100 yards is more than I can see any of my boats. Oh, I can see them, I just have no idea what they're doing...
- 'Doc

ernest2

gulfstreamI

Ernest2,

Nice boat! I shoud try jet dive boats for a change. The only r/c that I have that runs on jet drive is a submarine that was designed in 1987. I would'nt worry about the 27 mhz band use on your r/c equipment over there. Citizens Band radio operators over there on the 27 Mhz band have since disappeared in the early 90's with the introduction of GSM cellphones & those FRS walkie-talkies by Motorolla. Nothing but static since I last monitored the CB frequencies over there 2 yrs ago.

Have a great time with your project.
Mabuhay!

Gulfstream1

Kaskazi

I was/am planning to use DX6 in a largish tug, mainly because of the 6 channels. I plan a 12 volt system. I notice the servos that come with the DX6 are 3.2-6 volt. Is the whole system (receiver) limited to 6 volt? [You may gather that my understanding of electric stuff is not even hazy.]

LtDoc

Kaskazi,
It will depend on how/where your receiver get's it's power. If you use a seperate battery for the receiver the max voltage is limited to about 9 volts (9.6v) because thats what the voltage regulator in the receiver can handle. If your ESC has a BEC and that's how you are powering your receiver, then it'll probably work just fine since most BECs are set for output voltages below 9.6 volts (6 volts is probably most common?). There are two ways of knowing for sure, read the specs, or measure the voltage on the BEC pins from the ESC.
I have a tug running on 12 volts. BUT, the ESC doesn't have a BEC so I haven't had to worry about that aspect. If the ESC did have a BEC, I think I'd measure the BEC voltage just to be safe (make that read 'chicken'! - lol).
It's not that the servos are the limiting factor, but that the reciever is since it's also powered by the BEC. While replacing a servo isn't exactly one of my favorite 'things to do', replacing the receiver because I burned the @#$ thing up is definitely not one of them! And, since you really aren't gaining that much by using a 9.6 volt receiver/servo supply, and since that voltage level is right at the limit for the receiver, I think I'd stay under 9.6 volts by a 'comfortable' margin (6 volts works fine, lasts a long time).
- 'Doc

rszanti

Kaskazi

I believe the receiver is limited to a 6 volt supply. But if you control your drive motor with an electric speed control (ESC) that has a battery elimination circuit (BEC) it will reduce the voltage to 6 volts for operation of the receiver and servos. You do need to check the ESC to be sure it will handle 12 volts, some will only handle up to around 10.

You could also use a separate six volt battery pack to drive the receiver and servos and then use the 12 volt to power just the motor.

Richard

LtDoc

That 9.6 volt thingy is per 'Spektum's published specs. That's for the maximum voltage for the system (receiver), minimum is 3.2 volts (I think?). So something between those two should work just fine. Staying away from the min/max allowable ratings isn't a bad idea.
- 'Doc

Kaskazi

Thanks to LtDoc and rszanti. My ESC is a custom electronics job taking 12V and up to 10 amps. I went round to the local LHS and it turns out not to have BEC - no wonder I couldn't bind the receiver! I now plan to power the ESC/servos from a 4.8V 1500 mAh NMH battery pack, using the 12V for the motor as suggested. I think that should do it but I seem to have too many wires around my bench top. LHS says do this and do that and ignore this one etc. My head swims.

I can't bear to do any more with it tonight (!). I need some calm thinking time before I get back to it tomorrow.

But thanks again, and if calm thinking doesn't do the trick, as is quite likely, I may come back to you with some specifics.