gmsl

[&o]
Built a large scale Katana, all high torgue Futaba servos (9304). Using a 6v NiMh battery the servos flutter and generally misbehave as if the receiver was getting interference. The throttle servo does not function at all. Elevator servos do different things even though connected together with y-lead and servo reverser. Rudder flutters when coming back to centre position, but stops with a light force applied. All radio gear in aircraft is brand new. When a 4.8v NiCd battery was installed, all problems went away! Transmitter is Futaba 7UAPS.

Has anyone else experienced this problem and if so what could be the solution when using a 6v rec bat?

Another question is when should you use ferrite cores on servo leads? These are about 700mm/30in log.

Thanks.

Greg M

blikseme300

My Feedback: (118)

Hi Greg

I have had this kind of behavior when one of the servos I was using did not like 6v. When I connected S148 standard servos to the same RX and used 6v there was no problem. Try to eliminate this by starting with one servo and adding them until this occurs. It might not be the case with what you are experiencing but try to eliminate the cause.

Safe flying

gmsl

The problem only started as I added more servos and testing throws etc. Wasn't evident with only one servo connected! The eird part is how the throttle servo won't function at all.

hilleyja

My Feedback: (3)

gmsl,

Read between the lines of blikseme300's post. He is saying that one of your servos might be the overall problem. Is your throttle servo also a Futaba 9304?

Is your receiver new or an older vintage like your TX? I know there are Futaba gyro/servo combinations that definitely will not work with 6 volts -- their instructions are clear in that fact. Is your battery kosher -- have you cycled it to make sure it is performing at its rated capacity?

Test your setup by connecting and disconnecting servos in combinations. Try a different RX. Try a different switch. Heck, try a different 6 volt battery.

NOTE: One bad servo can effect the entire flight pack. Something might be wrong with your RX. Even your power switch could be the culprit.

gmsl

Jim,
Yes, the throttle servo is different however the problem occurs when its not connected. The Rx is new as is all the radio gear in the aircraft, plus I think the bulk of the rx, switch etc must be OK if it all works fine with a 4.8v battery. The 6v NiMh is also new and has been cycled. I'll keep isolating bits to narrow down the problem, but was interested to know if anyone else has had any issues with 6v on the Futaba receivers.

Greg

Bax

My Feedback: (11)

Please see if you get the same problem with an NiCd pack. A lot of high-torque servos can pull a lot of current. NiMH packs usually don't have the ability to push as much curent as NiCd packs.

You may also need to go to larger-diameter wires, especially with the long wiring runs. A heavy-duty switch harness might also be a consideration.

When going to heavy-duty servos with longer runs, standard wiring isn't up to the task. You're running higher current, and the resistance of the wiring can pose difficulties. Multiply this if your battery pack just can't deliver the current needed.

gmsl

Bax, Thanks. Is there a distance/length of servo lead when the larger diameter wire is needed, just a ball park number? Also do you have an opinion on the use of ferrite RF filters on servo leads?

Greg M

gmsl

Bax,
Another thing I was thinking about re your comment on larger wires. If we use a higher voltage battery 6V in lieu of 4.8V then the current will be less for the same power output. Do you think we need to use the larger wire on all high torque servos regardless of the batery pack?

Greg M

BillS

Greg,

If you search and read through the entire servo searching problems in this forum I think that you will conclude:
1. Most servo searching occurs on a fully charged 6-volt battery when the battery is about 7 volts.
2. After the edge is gone from the fresh charge the searching will stop.
3. Some servos will exhibit the problem while some will not even though they may be the same type from the same manufacturer.
4. The cause is almost always too many servo connectors or resistance in the crimp connections.

My experience has shown that removing the resistance in the connectors will stop the problem entirely. I use a solder station and put a minuscule amount of solder in each crimp connection.

Hope the information helps.

Bill S.

gmsl

Thanks Bill, I'll run the battery down a little to see what occurs. I hve already soldered all the connections to cut down on the joint resistance.
Do you have an opinion on using the larger servo cable for these high torque servos and RF filters on the cable?

Greg

BillS

Greg,

My experience has been that neither filters nor a voltage regulator helped the searching problem.

My guess is that at about 6.6v searching will be gone.

Heaver cable seems logical to prevent voltage drop but I have been unable to observe any difference in operation. I prefer heaver cable for runs over 18”.

Actually I think the problem exists in the signal line and not in the power lines.

It is good to remove the number of connections. But to clarify the crimp joint was soldered. It requires carefully taking each connector apart and soldering the three crimp joints with a miniscule amount of solder so they will go back together. Even with a solder station and magnifier occasionally a connector is damaged. Occasionally a crimp will pull apart with the slightest pressure and it should have been a reject. Resistance as low as 0.4 ohm across the crimp seems to cause the searching problem. Generally JR cable has seemed better than Futaba.

Hope the information helps. Have fun.

Bill S

Geistware

My Feedback: (16)

I have a wire load calculator on my site to help to understand the voltage loss for particular gauges of wire.

laryboy

My Feedback: (2)

the current will be more if you use 6v