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[dodgy geezer]

I've just been doing a range comparison between a 27mhz and a 2.4Ghz set as part of an examination into Taycol motor interference. It will take some time to go through all the tests I want to make, and then I'll write it up for the Taycol website, but I thought people might be interested in some initial findings.

I took a board, bolted a battery, three different Taycol motors which had particularly bad sparking, two receivers, an ESC and a servo to it, and walked it to different distances while observing. I used cheap radios (Futaba Attack and Radiolink T4U) and the dreaded 'blue' esc to try and get a 'worst-case' situation. I was able to switch inductors and capacitors in and out of connection in order to observe their effects....

I noticed the following points:

1 - I needed an inductor in the power line immediately for the worst of the Taycols - line-born interference was sufficient to stop the esc working properly. An inductor on each line completely cured that.

2 - the 27mhz link was fairly glitchy at all times. Capacitors improved this somewhat, but things got steadily worse as I moved away. Control was pretty ineffective and jittery at 400ft, which I counted as maximum range. That seems low, and I will do more work on this.

3 - positioning of the aerial made quite a difference to the 27Mhz system.

4 - the 2.4Ghz system was unaffected by radio interference - even when I positioned the aerial directly against the motor. I still needed an inductance to keep the esc working.   

5 The 2.4Ghz system operated smoothly and effectively without any capacitors on the motor at a good range. I was in a set of fields around 2500ft long with a hill at 1750ft away. The radio functioned well up to the top of this hill, and fairly far down the other side, though this was out of direct line of sight. It stopped responding at about 2200ft (this was, of course with a hill in the way). This is about 730 yards - about 0.4 miles. I suspect that if I had line of sight, or if it was in the air it would have operated a lot further. This was with an aerial lying flat behind a large metal engine. 

I don't know what people expect from a radio at ground range. But I think the furthest distance I have ever operated a boat at has been about 1000 ft. It seems to me that the cheap Radiolinks do quite a good job of operating at distance...

[CF-FZG]

Can you explain better what you mean by 'inductor' please?

From the depths of my memory, an inductor is what we used to call a choke, so I'm not sure how you're fitting one onto a power line??  or do you mean you're winding the power lead through a ferrite ring (or similar)??

Ground range is quite dependent on eyesight in 'practical' use - range testing is a different matter where you can find the maximum range possible.

A 1000 feet is just over 300 meters, I think I'd have a problem picking my car out of a 'line-up' at that distance, never mind trying to find a small model boat.

The point about not requiring caps on the motors with 2.4 is (sort of) expected - how was the servo reacting to control on the 2.4 system at the same time?


Mark.

[dodgy geezer]

Yup - power line wound round a ferrite ring. The enclosed picture of the test rig may help to indicate what's going on.


Here I was looking for max ground range. One point to make is that this will vary quite a bit with 27Mhz depending on what attitude the aerial is at, while it seems to make little difference with 2.4ghz...

A 1000 feet is just over 300 meters, I think I'd have a problem picking my car out of a 'line-up' at that distance, never mind trying to find a small model boat.

I was young, and the reservoir was flat, waveless water. You could work out what was happening by watching the dot at the head of a wake. I thought it was a hell of a distance, but I measured it on Google Earth and reckon it was about 1000ft...

The servo on the 2.4Ghz ran smoothly at all times and distances - motor on or off. I walked to about 2000ft - still fine.  I walked to 2500 ft, no response at all from servo or motor. I walked back to 2200ft, all fine again...

Of course, you should have caps on your motor on a pond, even if you are 2.4Ghz, because someone else may not be....

 

[malcolmfrary]

To be more effective at RF, the choke windings need a bit of a gap between start and finish to reduce the chance of the high frequency hopping over and ignoring the winding.
The motor brushgear also needs a spark quench to give the back emf somewhere to go before it runs into the choke.
Did any of the checks involve running the motor direct off the battery?  This would eliminate any feedback into the ESC via the motor leads, running the motor on a separate battery would further eliminate any spikes appearing direct on the power leads.

[dodgy geezer]

To be more effective at RF, the choke windings need a bit of a gap between start and finish to reduce the chance of the high frequency hopping over and ignoring the winding.

As you may have guessed, these are chokes lifted direct from an old power supply board. That was how they came off the pcb. I wasn't sure if I could wrap both power leads round one core, or whether I needed two - in the end I just did what you see. It had an immediate effect on the ESC, making it work perfectly, so I saw no reason to improve the windings. But thanks for the pointer - it will go in the eventual Taycol write-up.  Can you just use the one ring with two separate power wires?

The motor brushgear also needs a spark quench to give the back emf somewhere to go before it runs into the choke.

Is that the same as a spark gap? Or are you talking about a resistor across the brushes? Or something else entirely?

Did any of the checks involve running the motor direct off the battery?  This would eliminate any feedback into the ESC via the motor leads, running the motor on a separate battery would further eliminate any spikes appearing direct on the power leads.

I didn't have the wiring set up to do that this time, but it will be on my list of things to do for further 27mhz testing. I did, of course, check the servo with motor on and off, which should get a similar effect. The findings tended to show that you hardly need to worry about suppression of any kind for 2.4Ghz, but it's a huge issue for 27mhz (and presumably 35Mhz and 40Mhz). I was very unhappy with the range of the Futaba, and need to revisit that test - perhaps after cleaning the TX battery contacts well. They were dull and one was corroded - I scraped it and got a reliable turn-on and full voltage indicated with new batteries, but it might have been unable to pump out full amps?

I was, however, impressed at the range of the Radiolink. I hear statements that these cheap Chinese items have a limited range - but the best part of half a mile ground range seems ok to me. And that had quarter-used batteries Does anyone know what a top-of-the-range set can achieve?   

[CF-FZG]

Does anyone know what a top-of-the-range set can achieve?  

There was an article by a US online mag a few years back that tested a DX7, (although it might have been a 9303), to find how far you could operate the system with 40+ other 2.4 sets operating at the same time.  IIRC they were getting around 1/2 mile of reliable ground range.

The test was that all the Tx were on tables at the same location, and the Rx test set, (operating 5 servos IIRC), was mounted on a plank of wood and dropped into the back of a pickup truck, which was then driven along a 'under construction' road and recorded on video until things stopped working properly, they had a small rise around 1/3 mile and started loosing channels at around 2,500 feet and it went into failsafe at about 1/2 mile.  They aslo had a JR Mhz set and Fubaa and hitec 2.4 sets on the same test, and apart from the Mhz set which was slightly shorter range, the other 2.4 sets were around the same distance with no other sets switched on, but slightly shorter range when they switched the other 40+ DX7s on.

They repeated the test using a full size Cessna to find the 'air range' and got around 3.5 miles before losing the odd channel.

[dodgy geezer]

Don't suppose you have a link to that?

I've looked for it on the net, and mostly I find people doing air range tests. I'm not too sure how far people need to connect to a boat, but it looks as if these cheap Chinese sets have a similar range to the top price systems....

[richald]

DG

I've come across people turning their noses up at Radiolink equipment due to 'lack of range'.   

Your tests seem to have knocked that complaint into a cocked hat !   

BTW, glad you got the channel five lead OK

Regards

Richard

[malcolmfrary]

I was thinking back several years into a slightly different area.  The spark quench was intended to calm down back EMFs across relay contacts and can't really apply to brush gear.  However, the capacitor across the brushes does have the effect of catching any excess voltage spikes before they get as far as the chokes.  The voltage is still rattling around in its' source, of course, which is the armature coils.  Not 100% sure just how the field coil would figure in this, or whether it would simply be insignificant.
Can't think of a good reason why the two leads should not sit on the same toroid.  When I was trying to keep radar and Ham radio out of telephones it was the cords that got wound onto the ring (one ring per cord) so that effectively the wire with the current "coming" was closely associated with the wire carrying the current "going".  In that case, it proved advisable to basically wind as many tight turns as possible, but keeping the gap was important.  For ease of measuring, it was the width of the tape used to fix the cord down, 0.5in.  If putting two wires on, it will be important to ensure that a) the insulation will withstand the voltage (remember back EMFs) and b) that both wires retain their proper current direction, else it might be possible to actually boost the interference value.

[dodgy geezer]

I've come across people turning their noses up at Radiolink equipment due to 'lack of range'.   

Your tests seem to have knocked that complaint into a cocked hat !   

Yes - I have heard people saying that the Planet has a limited range - but I can't see why it should have. Perhaps someone with a Planet will do a little pondside walk next time they are out?

BTW, glad you got the channel five lead OK

Yes - thanks very much for that...

[CF-FZG]

Don't suppose you have a link to that?

I've been looking today and can't find it - what's really annoying is I posted the link on another forum and can't find the post now.

Ooookay, I think I've found the reports, they were by Cal Orr - unfortunately they were shown on the Spektrum website at the time, but under permission from either Fly RC or RC Report around May 2008 .  Now these are both subscription sites so it kinda explains why Spektrum and JR no longer have them available

I'll keep looking as I'd like to confirm if my memory is accurate


Mark.

[dreadnought72]

Many thanks for the range info - it's fascinating reading, and I'm very impressed with modern radio gear.

But a quick check using Google Earth finds that my daughter's house front door is 260 metres from my own: about three minutes' walk away. At that distance, the Racundra's 80cm tall mainsail would be one third the size of the full Moon.

That's plenty far enough for any sensible degree of control and visual feedback to be a limit, I would think.

So - given that all radios seem at least "ok" well beyond these practical ranges - wouldn't a better test be seeing how reliable signals and control are, over water, and with nearby sources of interference acting on the TX?

Andy

[dodgy geezer]

So - given that all radios seem at least "ok" well beyond these practical ranges - wouldn't a better test be seeing how reliable signals and control are, over water, and with nearby sources of interference acting on the TX?

If you've got a specific test protocol in mind, I'd be happy to comply. The advantage of simply measuring how far a signal can be detected is that it was an easy and unambiguous test to make. I'm not sure how I would measure 'reliability'?

[cuppa]

I did a ground range test on the planet 5 system i had and, although I did not accurately measure so this is a 'guesstimate' I would say that it was good for at least 500 yards - more than enough for any model boat that I will ever use.

The planet 5 did have an issue though with boats that introduce a fair bit of spray into the air. I am no expert but based on what I was seeing and have read I would say that the spray was screening the rx from the signal. I think that this may improve with a receiver with a longer aerial. After all plenty of folks use 2.4ghz in fast boats and do not report any issues.

What worried me was the delay between the receiver loosing the signal and the failsafe being deployed. During this period the boat would continue at its last 'good' throttle setting and heading until the failsafe deployed and brought the boat to a halt.

Having weighed up the pros and cons I decided to use 40mhz despite the obvious convenience of 2.4ghz. I felt more comfortable with 40mhz and a separate failsafe system. I guess I could have resolved this issue by using a system that used a longer receiver aerial so that more aerial was 'above deck' but I knew, based on previous experience (quite a few years ago I ran IC powerboats and never had an issue with 40mhz) that 40mhz would work well and so i opted for that.

Having said all that I would not hesitate to use the planet 5 2.4ghz in model boats travelling at more modest speeds.

[Circlip]

In the good old days of super-regen 27 moggies, ground range was generally accepted as half air range. After the sophistication of crystal control and transistorised gear, manufacturers were proudly proclaiming "Out of sight" range for toy aircraft. Given that the "normal" span at that time was 60", all the spec meant was that you couldn't see it crashing at 3/4 of a mile although the range was in excess of that.

   It's good to see someone (DG) filling in the blanks not specified by the "Lower" manufacturers, but many boaties seem to get hung up about "Range". Whatetever it is on 2.4 gigglies, it don't matter to those whose angle of declination is important.


     Regards  Ian.

[dodgy geezer]

I did a ground range test on the planet 5 system i had and, although I did not accurately measure so this is a 'guesstimate' I would say that it was good for at least 500 yards - more than enough for any model boat that I will ever use.

Did you test it out to the point where the receiver stopped working? 500yds (1500ft) seems a bit short, though, as you say, fine for boats in practice...

The planet 5 did have an issue though with boats that introduce a fair bit of spray into the air. I am no expert but based on what I was seeing and have read I would say that the spray was screening the rx from the signal. 

Aha - this sounds like a useful addition to a test protocol. Means setting up a hose, though.... 

[cuppa]

Did you test it out to the point where the receiver stopped working? 500yds (1500ft) seems a bit short, though, as you say, fine for boats in practice...
Aha - this sounds like a useful addition to a test protocol. Means setting up a hose, though....  

I did not test it until the receiver lost the signal. I just walked it way beyond the range at which I would use a model boat and it was fine. I was not trying to establish the absolute range but just to establish that it would work well in the circumstances under which i run model boats.

From what i have read 2.4ghz signals will not penetrate water to any great extent - hence not using 2.4ghz to control model submarines. This certainly concurs with what i was experiencing - the signal was lost when the rx aerial was screened by a plume of water. I do wonder if an rx with a longer aerial (FlySky for example) or twin aerials as some have (Spektrum etc) would to a great extent negate the spray screening issues.

I don't know if this is correct or not but I read on an American site that Spektrum only started advocating the use of their 2.4ghz rx's for fast boat use with the introduction of their 'Marine' range.

[dodgy geezer]

There seem to be a lot of stories about, and precious little hard evidence. For instance, I have seen commercial sellers state that the Planet has a short range - but you suggest that it has at least 1500ft ground range and, I suspect, up to around 2200ft, just like the RadioLink. I wonder if that seller wanted to sell cheap radios, but also wanted to edge his customers towards more expensive ones....

The 'water curtain' is of particular interest for boaters - I must see if I can set up something in the garden. Perhaps in the summer...   

[cuppa]

There seem to be a lot of stories about, and precious little hard evidence. For instance, I have seen commercial sellers state that the Planet has a short range - but you suggest that it has at least 1500ft ground range and, I suspect, up to around 2200ft, just like the RadioLink. I wonder if that seller wanted to sell cheap radios, but also wanted to edge his customers towards more expensive ones....

An interesting point.

As the maximum strength of the signal from the tx is regulated by law I think it is likely that most transmitters have a similar output signal strength and so, if this is the case, any quoted difference in range is down to the capabilities of the receiver. The range test I did was in a public park with no obstructions between the rx and tx and no other transmitters in the area.

Could it be that the cheaper receivers do not have the same spurious signal/interference rejection properties as the more expensive ones and so the statement of the workable range is reduced to allow for this?

[Netleyned]

I sail on a lake with a very large fountain in the centre.
It's about 100yards from our control point.
My yachts have the 2.4 Rx antenna at just above the waterline.
Using a T4U and a Spektrum Dx6i I have no loss of signal sailing
about 50 yards behind it.

Ned

[dodgy geezer]

Could it be that the cheaper receivers do not have the same spurious signal/interference rejection properties as the more expensive ones and so the statement of the workable range is reduced to allow for this?

That's what I've been trying to examine with the Taycol interference board.

What I think is more likely is that the top-end radios make a breakthrough with new systems, using custom parts which are expensive. So they have to sell them for enough money to recoup the cost of their investment.

Once they have 'shown the way', the custom parts become widely available, and other manufacturers start making sets using essentially the same components, but for much less, because they don't have to recoup this research and development cost.

In the case of 2.4Ghz, this is the same frequency which is used for computer Wi-Fi, and the components are dirt-cheap because billions are made. So you can make dirt-cheap radios.

The high-end manufacturers try to differentiate their kit, with higher quality and added features, so that they can keep selling at a higher cost. But, increasingly, there will be little difference between all the sets in terms of the basic functionality...

[barriew]

Aha - this sounds like a useful addition to a test protocol. Means setting up a hose, though.... 

There was an article in Model Boats (I think) a few years ago written by a member of this forum - Wideawake? - about testing the Spektrum DX5e. He used a hose to try to test the effectof a sheet of water - sorry I can't remember when this was exactly, maybe 2008, or the conclusions of this test.

Barrie

[dodgy geezer]

Shame - it would be nice to reproduce his test on a cheap 2.4ghz and see if it got the same results...   

[AlisterL]

Try this link (and the rest of this site for that matter. He has some very interesting stuff):
http://rcmodelreviews.com/spreadspectrumtests.shtml

Err, no testing of the Planet T5 or Radiolink however - that stuff doesn't seem to be available in this part of the world...

Testing, it seems to me, is very well thought out and the same methodology is used for all tests.

(I know this should go in the thread about the 9x - but here's the 9x review: http://rcmodelreviews.com/turnigy9xv2review.shtml)