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Hitech 5645mg fails during installation

Old 05-20-2005, 09:59 PM
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Todd D
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Default Hitech 5645mg fails during installation

Hey guys,

I'm putting some new Hitech 5645mg servos in my funtana 90 and one of them failed after installation during rigging. Basically it started to move around on it's own quite a bit, not just little jitters but a lot of deflection. It didn't start this instantly when turned on, but maybe after 1/2 an hours worth of rigging and adjustments. I thought maybe the RX had a bad channel, I switched the servo to a different channel that worked fine with an identical servo and it had the same problems. I then shut everything off and let it sit for an hour or so and tried again and it seemed to work normally, perhaps being on for a 1/2 hour or so during rigging causeed the failure? I have to suspect the servo is bad and don't wan to fly it on a brand new plane. Anyone had similar problem with this servo?
I am running a 6volt battery that read 6.48 volts when the servo failed, I checked thinking maybe the battery is running down. Is running a 6 volt battery with these servos ok?
I'm new to digital servo's, am I doing something wrong?
Setup is 5645mg servos 5ea, Futaba 9cap radio and Futaba F149DP PCM RX, 5 cell (6volt) 1700mah battery.
Thanks for the responses.
Old 05-20-2005, 11:41 PM
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mglavin
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Default RE: Hitech 5645mg fails during installation

6.0V is fine...

Did you try another known working servo in the same location same time to verify the servo itself was the problem?

Charge the battery and try again. Did you check the battery voltage under a load, at least a 1/2 amp?

Cycle the servo connectors to ensure good contact.

Is a wye in line with this servo?

It's plausible the servo is defective if nothing else.
Old 05-21-2005, 08:38 PM
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Todd D
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Default RE: Hitech 5645mg fails during installation

Michael,

Thanks for the reply.

No I didn't try another known good servo in the same position (channel 8) onthe PCM RX. But, I did try that suspect servo in another channel on the RX, (channel 1) and it exibited the same behavior.

I checked the battery voltage with a hobbico digital voltmeter that supplies a load to thte battery. I'm not sure how much of a load it is. The battery started at 6.48 and dropped to 6.40 under a load for 15 or 20 seconds.

No y harness in use, just direct servo extensions to each elevator servo, from channels 1 and 8 on the PCM RX. (the suspect servo is on the right elevator half)

The thing that bothers me the most is that servo was fine for the first 30 minutes or so and then started to exhibit these glitches.

Wouldn't it make sense that if it were a connector problem that it would show up all the time, not just after being powered up for 30 minutes.

Thanks again for your reply.
Old 05-21-2005, 09:01 PM
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Default RE: Hitech 5645mg fails during installation

A connector or resistance problem will exhibit an increase in heat and electrical losses over time.

As I mentioned the servo maybe at fault and as it warms up it begins realize a problem. How about playing with the servo outside the model and or directly coupled to an RX to eliminate any electrical losses that might be realized of the extensions.

Try connecting the suspect elevator servo to the opposite side extension and test again.

The problem with extensions and wyes causing or propagating these problems is common place. Eliminate these things and try to recreate the problem before delegating fault to the servo.

Is there any binding or unnecessary resistance in the surface of the problem servo? Proper set-up with high power digitals is a must.

Another thing that may play a part in this; 1/2 hour set-up with the TX down will heat the RF section of the TX, this is a not a good thing.
Old 05-22-2005, 05:33 PM
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Default RE: Hitech 5645mg fails during installation

Mike,

Thanks again for the response. I will do some more troubleshooting and see what comes of it.

One more question. I usually extened the antenna of the TX the first segment when doing adjustments and such as I've heard elsewhere that I shouldn't leave it fully collapsed. Does it make a difference how much to extend it, 1 segment, 1/4, 1/2, 3/4, fully? Whats a good rule of thumb for this?

Thanks,
Old 05-22-2005, 06:06 PM
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Default RE: Hitech 5645mg fails during installation

Any extended time with antenna down will over heat the RF section. I don't know for sure but suspect the problem decreases as the antenna is extended.
Old 05-22-2005, 08:57 PM
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Default RE: Hitech 5645mg fails during installation

Okay, thanks again.

Problem is isolated to the servo.
Long story short, the servo started to exibit the same jittering again while installed as before. Removed servo and extension from aircraft. Attached to RX same channel outside plane and same problem, cycled connector at extension same result, removed extension and plugged servo directly to Rx same result, tried several different channels same result, conclusion, bad Hitec digital servo. I will return to them.

Thanks for the help
Old 05-22-2005, 09:50 PM
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Sailor
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Default RE: Hitech 5645mg fails during installation

Twist,

I had the same symptoms as you on a brand new 5945, and yes, it was the servo that was bad. It appears that the Hitec digitals will go bad on you, if they are going to go bad, with in a short time span. I sent it into Hitec and they replaced it was a brand new unit that has worked flawlessly. Just an FYI.
Old 05-22-2005, 10:20 PM
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Todd D
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Default RE: Hitech 5645mg fails during installation

Sailor,

Thanks for the reply. I certaintly hope these are isolated case's as I know quite a few people who fly Hitec digitals. I guess if it's going to fail, it's best to happen during setup and not in the air.
Old 05-22-2005, 10:43 PM
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Default RE: Hitech 5645mg fails during installation

It is a good practice to bench fly all new servos. I run all new servos in test mode on my 9C, usualy for one hour in 15 minute cycles, after all set up is complete. This will catch 99.9% of all electronic infant mortality.

At least I hope it does!
Old 05-23-2005, 11:09 AM
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MustangFan
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Default RE: Hitech 5645mg fails during installation

I agree wholeheartedly !
Bench test for 45 min to 1 hour

Old 05-23-2005, 04:42 PM
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Todd D
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Default RE: Hitech 5645mg fails during installation

Yes, that will be standard practice going forward for sure.

As stated before thankfully this manifested itself during setup as this would have certaintly brought down the plane if it happened in the air.

One last note to this; I ran the servo agian before packaging to return to Hitec on a 4.8 volt battery instead of 6 and a standard Futaba RX instead of a PCM, low and behold after 15-20 minutes, same results, servo moing all around by itself.

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