PPM with Futaba 401 Gyro

[Tripler]

Hi
I've been told that using the 401 gyro with PPM mode can cause problems
giving the odd twitch or kick from the tail because the gyro does'nt like the
PPM signal and responds better with PCM,
Is this true??
All though I don't like PCM mode, because of its long signal and long response
checking time and deciding weather to go into fail safe or not before it switchs back on, were as with PPM you just get a glitch,,

Is it worth changing my RX to a PCM?

Cheers

[ChrisB]

I have never heard of this at all,i am using the new 611 with PPM and thats fine,many fliers i know use the 401 with PPM with no problems..

I am NO electronics guru but i think the signal type is only relevant to the RX,what the Rx outputs to the servos,gyro etc is the same signal whatever the transmission type..

[Ade_Law]

some recievers do get upset by digital servos. the 9254 doesnt appear to be a noisey servo so seems ok. As Chris said i have used PPM with 401 and 601 without problems but those were Schulze recievers.

there are a few people that hate PCM and i am not really sure why. They make it sound like PCM will lock out when it feels like it.

the truth of the matter is that PCM will carry on working long after the signal noise is enough to turn PPM in to a gittering wreck.

all my lockouts have been down to rough bearings or loose bolts. 99% of them are just partial locks where the controls just go quiet for half a second. Thats a warning that things are not well and it needs a good check over.

if you ignore these quiet times then you stand a chance of it locking out completly.

the major advantage is that if somebody switches on their tx on your frequency the receiver goes into failsafe throttle drops to zero and you end up with a model with very little energy hitting the ground, people or property.

ppm might well be quicker in theory but i doubt many will notice the difference in the air.

Ade

[Dedcalm]

I currently use PPM mode with a 138DF Futaba receiver and have never had a problem with either the Rappy or previous heli. I currently have a 401 on the tail with a 9254, 9252's on the pitch and cyclic and a 9254 on throttle through a TJ Pro. Cant get more digital than that!

Am looking to go PCM sometime soon though as its a lot of £ to go awol due to a failed Rx/comms.

Rob

[ChrisB]

Im gonna go over to PCM myself as i need new Rx`s,they are getting a lot cheaper now also.I have used both pcm and ppm with no real problems but i have always wondered which is best.PPM may show every hit but at least you have control throughout the problem but its a case of how much control you have,you could lose the heli and it would go in and possibly hit something or somebody going at full pelt,PCM at least is more resistant to hits and if it does get one you only get about a quarter to half a second lockout,its not that long i know but long enough to allow the pilot to realise there is an issue and land it,if you get a major hit that continues or maybe somebody switches on to your channel you will get a total lockout meaning zero control,a crash would be inevitable but at least with the failsafe option you can centre controls and cut engine to idle minimising any impact damage to your heli and god forbid and person or object that found themselves in the new flightpath of the model.
In reply to the original post i have always found that the gyro is the first control to show a glitch with a little kick of the tail,i have had this problem myself but it was due to static discharge from a tail drive belt.

[Dedcalm]

Shutting the engine to idle is good if it does go in as well, nothing worse than seeing your expensive engine at max unloaded revs on the ground! Repairing the heli is expensive enough without having to replace the piston/liner/engine as well...

Anyway I am off to charge up the heli as I may get time to give it its 1st flight this year!

Rob

[Steve]

I've got a 401 in my Voyager with PPM and it behaves just fine - much better in fact than the CSM 420 that it replaced.

[Tripler]

Thanks for all your comments chaps!!
Did'nt think I'd start a full debate about the sudject!!

I've been flying the Raptor with the 401 and 9254 using a df138 RX for a year now without any major problems
So I think I'll save money for now and stick with PPM

Although I've just upgraded all other four servo's to Futaba s3152's digital's
Fitted a CSM revlock and currently trying to get hold of a 3600 Rx bat to compensate for the extra drain,,

Do you think this setup is ok?

Thanks

[Leebert]

Hi Tripler
I am thinking of going down the 3152 route myself. What did you have before and has it made a big difference??
Cheers,

[Steve]

I've recently gone over to Futaba 3050 digis on both my 30 and 50 sized helis - have definately improved the accuracy of the response, especially with the 30 sized CCPM heli.

I use 3600mAh batteries in both my 70 and 50 sized helis and a 2400mAh in my 30 size. I've never done more than 6 flights in any one afternoon with any one heli, and the battery monitor didn't drop below the 2nd green light.

The secret to good batteries is good charging and cycling. I've got some Mainlink Systems stuff - a quick charger and a cycler, and it works a treat.

[Tripler]

Hi Leebert

I had the standard Futaba s148's that came with the Futaba T7CP TX
bought the lot from skyline and took their advice on what to buy as a beginner,,

The new 3152's have got rid of slack and play the old servo's had from new
and they seem to be slightly quicker and more responsive,
I have'nt flown it enough to really make a judgement, but going on my first
reaction i would say its certainly made a difference for the better.

Cheers

[Ade_Law]

i recomended 2400 nicad for all helis. minimum of 4 flights on an all digital 50 size.

on 90 size the current drain is much higher. whilst you can get quite a few flights out of them safely the voltage during the high loads can be very low. So its best to fly once then top up.

you still cant beat a li-poly or li-ion with a regulator. constant rx voltage no matter what the state of the battery and up to 15amps from some regs.

Ade

[Raptorite]

I have heard of and even had this problem myself. It is actually that if the gyro senses more than three glitches in the signal being sent to it, it will reset the neutral point in AVCS (heading hold) way over to the left, therefore to keep the model flying in a straight line, you need to keep in a fair amount of right rudder.

The reason people suggest using PCM receivers is that they are equipped with failsafe, therefore they mask any glitches from downstream devices such as a gyro by maintaining channel signals as per the failsafe settings. Obviously PPM receivers dont have this capability, therefore any downstream device will also see the glitch as a momentary loss of signal.

I know futaba gyros do this, I have had it with GY401's and GY502's I havent ever run a GY601 with a PPM receiver, but as the software is so similar to that of the GY502, one would assume it would behave in exactly the same way. Again I cant comment on the GY240, as I have never run one with a PPM receiver, but as the gain on the GY240 is set on the gyro itself rather than on the TX, one would assume it would not be affected in the same way.

Cheers,
Pete.