Help: Futaba R608FS FASST ch 6 can't drive 2 servos

[wwurjant]

I'm trying the question again. My last thread was accidentally killed.
I recently purchased a Futaba Fasst module TM08 and a R608FS FASST receiver.
These went into a 50CC bipe with ch 1 and 6 mixing for ailerons.
Each of ch 1 and 6 drove 2 Hitec 5645 Servos. It turned out that ch 6 didn't have the power to drive the 2 5645's.
Just to check, I demixed ch 6 and assigned it to a dial on my 9C transmitter, and it still couldn't drive the servos. I tried this with channels 1, 2, 3, 4, and they were okay with driving 2 5645's.
I took the receiver back to the hobby shop, showed them the failure, and ask the staff to try the same experiment with another Futaba R608FS FASST fresh from the shelf. To everyone's surprise, it had exactly the same problem.
Has anybody else seen this? Was this expected? Is there a workaround ?
For comparison, my PPM Futaba receiver has no problem driving 2 5645's per channel. Also,Ch 6 on R608FS could drive 2 standard servos without any problem.
So, this seems to be power/current drive issue.

If anybody could share any information on this issue, it would be greatly appreciated.

Wisnu

[xed]

It is the 2.7v signal voltage issue that has been documented elsewhere. The servos are not able to handle the lower voltage that the Futaba receiver is sending.

[BR289]

I do believe that if you sent those servos to Hi-Tech they could adjust them to accept the lower current for you. Give them a call first to check that out.

[Pale Rider]

How old are your servos ? Reason I ask is the 608 rx has an output signal voltage of 3.0 so there shouldnt be any problems unless your Hitecs are not recent. Hitec will upgrade them for free so this may be your problem.

[JVDO]

with a powerbox or emcotec the problem will be solved too!

[wwurjant]

Thks for all the replies everyone!!
I purchased my Servos in the Summer of 2007, but I only used it in 1 flight.
If this were an issue of not enough current/voltage, how come it only happens with channel 6?

Is Futaba planning to adjust Ch 6 to make it behave like other channels?

If I were to go with adjusting the Servo to accept lower current/voltage, wouldn't this reduce the servo's torque and risk a flight failure?

In the meantime, I'll check out the powerbox solution.

Thks again!!

Wisnu

[JVDO]

You can have problems from channel 3- ....

[wwurjant]

Oh, I think I left out an important fact:
Ch 6 of the R608FS could drive a single Hitec 5645 without any problem. As soon as I plugged in the other 5645, the problem showed up.
I'm not too sure if I fully understand, but this seems to rule out the Hitec servo voltage problem doesn't it? Unless the voltage on Ch 6 would drop when 2 5645's are connected to it.

Wisnu

[Pale Rider]

The issue seems to be only if using 2 or more on a single channel. I have 2 R149 PCM rx's and have been using dual 5955's on channel 2 with no problems. The output voltage is 3.0 which is the same for the 608.

[crhammond]

Supposedly the 608 has a 3.0v signal so that should rule out the problem.

One way to check it is to put a Y-connector on one of the other channels and see what happens. If the servos stay still and then "go nuts" if you manually giggle them then it has the voltage problem.

I was told by Hobbico last week that the 608 didn't have the 2.7v issue... but maybe I was told wrong.

I think it's time to get out some equipment and check the levels on my 608's!

[Pale Rider]

	Quote: Originally Posted by crhammond
	Supposedly the 608 has a 3.0v signal so that should rule out the problem. I was told by Hobbico last week that the 608 didn't have the 2.7v issue... but maybe I was told wrong. I think it's time to get out some equipment and check the levels on my 608's!

Same here--I was told by 2 different Futaba reps as well that the only FASST rx that had this issue is the 6014. I have a 617 FAAST and tried dual 5955's on every channel and they work perfect.

[Spaz]

	Quote: Originally Posted by wwurjant
	current/voltage, wouldn't this reduce the servo's torque and risk a flight failure? In the meantime, I'll check out the powerbox solution. Thks again!! Wisnu

it's not the power (voltage and current) supplied to drive the servo, its the signal voltage that tells the servo where to go, i would send the servos in to get checked and or upgraded.. or get futaba servos

[wwurjant]

	Quote: Originally Posted by Spaz
	it's not the power (voltage and current) supplied to drive the servo, its the signal voltage that tells the servo where to go, i would send the servos in to get checked and or upgraded.. or get futaba servos

OK, I realize now that's it's the control, not the power. But, if it's really the control voltage issue, that doen't explain the fact that there's no problem with channel 6 if I only use a single Hitec 5645.
As somebody mentioned, the problem appeared only if 2 servos are used. Does this mean the control voltage dropped as soon as I connect the second 5645 ?

Wisnu

[crhammond]

Futaba says te [problem may show up with het (i.e. when the servo gets warm.) The problem shows with a Y-cable. I don't know the technical reason why.

Anyway - like I said if you want to test it then use any channel with a Y harness and 2 Hitec digitals and see what happens.

I haven't had a chance to test my 608's yet... but I will.

To be 100% sure use a buffer (amplier, power board, etc) and/or have Hitec make the modification to your servos.

[wwurjant]

	Quote: Originally Posted by crhammond
	Futaba says te [problem may show up with het (i.e. when the servo gets warm.) The problem shows with a Y-cable. I don't know the technical reason why. Anyway - like I said if you want to test it then use any channel with a Y harness and 2 Hitec digitals and see what happens. I haven't had a chance to test my 608's yet... but I will. To be 100% sure use a buffer (amplier, power board, etc) and/or have Hitec make the modification to your servos.

Thks for the suggestion.
I already mentioned channels 1 to 4 were okay with driving two 5645's. Didin't bother testing CH 7 and 8.
This seems to suggest to me that the problem is with the 608, not the servo.
But I'll dig more into it.

Wisn