2 wire Servos???

According to Tower Hobby, their System 2000 Dual-BB Giant scale Servo
TS-80 comes with 2 (NOT 3 wires).
They also say that the third wire is not necessary.
Please, someone enlighten me as to how this works.
Also, how to wire it to the battery plus the receiver for its higher
current draw,
Does one place the full voltage across it in parallel to the receiver
output?
Please unconfuse me.
Reply to
BoyntonStu
Loading thread data ...
I'll try ;-)
That servo depends on the same electrical connections as any other: power, ground, and control signal (with the standard 1500 us neutral spec as any other servo).
That said, because the high power requirement for this servo could damage standard receivers (which simply may not have enough metal in the power path to the output connectors) the servo must be connected directly to a power source (battery) as well as the receiver output.
To accomplish this you attach a Y cable to the servo, with one lead going to the receiver (for control signal and ground reference) and the other going to the battery pack (for power and ground reference).
Cheers
/daytripper
Reply to
daytripper
| | | >According to Tower Hobby, their System 2000 Dual-BB Giant scale Servo | >TS-80 comes with 2 (NOT 3 wires).
No, that's not what they say. Not on the web page, anyways.
| >They also say that the third wire is not necessary.
They don't say that either.
| That servo depends on the same electrical connections as any other: power, | ground, and control signal (with the standard 1500 us neutral spec as any | other servo).
Yup. It just has two sets of power connectors, so it can get more power.
The item is actually here --
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... though to be fair, it does sort of look like, in the picture, that the servo only has two wires. But it's hard to tell -- it could just be that two of the wires are black, and the third red.
Either way, I'm pretty sure it has the usual three wires.
`Running w/No Load: 700mA' ... wow, that's a lot. Imagine if you actually put a load on it! :)
Reply to
Doug McLaren
" Either way, I'm pretty sure it has the usual three wires."
Nope, only 2!
I called Tower Hobby and they confirmed that the middle signal wire is NOT on a TS-80 or is it necessary.
EVERYONE thinks otherwise, hence my confusion.
If you parallel the 2 wires to the receiver and the battery, I believe that this comment below would be problematic because the servo would continuously turn due to the applied DC voltage.
"That said, because the high power requirement for this servo could damage standard receivers (which simply may not have enough metal in the power path to the output connectors) the servo must be connected directly to a power source (battery) as well as the receiver output."
How do you connect a servo directly to a battery and not have it turn?
What am I missing?
Reply to
BoyntonStu
On 02 Aug 2007 14:46:18 GMT, "Doug McLaren" wrote in :
I'll bet that it just has two as a safety feature--if plugged into a receiver directly, it probably won't work.
The magic is in the Y cable that is supplied with the servo:
COMMENTS: Universal Y-Harness: Because This Servo has a High Current Drain, the Y-Harness is Used to Plug the Servo Into the Receiver and Also to Wire Directly to the Battery Pack for A Power Sorce. This is Done so the High Current Does Not Damage the Receiver. It is Up To The Modeler to Hook Up the Power Supply Wire to the Battery. Diagram-> (F end) Servo-\---->Receiver (male end) \-->Power Sorce Battery (male end)
I'm not going to put a lot of money on this bet. :o)
Marty
Reply to
Martin X. Moleski, SJ
jeeze, having a little trouble with your newsreading today or what?
/daytripper (who had everything he said clipped - then repeated ;-)
Reply to
daytripper
| I'll bet that it just has two as a safety feature--if plugged | into a receiver directly, it probably won't work. | | The magic is in the Y cable that is supplied with the servo:
No, there's no magic at all.
It's a standard servo, with standard wiring, but comes with a Y harness so you can get power directly from a battery rather than getting it _through_ your RX.
They could have made it with four wires coming out -- two go to your battery, and two go to your RX (signal, ground) -- but certainly there is not only two wires total. Perhaps the harness only has two wires going to the battery and two wires going to the RX -- but it certainly has three wires going to the servo.
Lots of giant scale plane guys wire their servos like this, with power for the servos not going through the RX at all.
It would be possible to make a servo that really does only have two wires, getting both signal and power through these two wires, but it wouldn't be compatible with our current gear, so why bother?
| I'm not going to put a lot of money on this bet. :o)
Probably wise.
Reply to
Doug McLaren
| jeeze, having a little trouble with your newsreading today or what? | | /daytripper (who had everything he said clipped - then repeated ;-)
If you're referring to my post, I didn't clip everything you said, and didn't repeat everything you said either. Though I did agree with you.
I don't have to disagree with you to follow up to your posts, do I? Did I miss the memo?
Reply to
Doug McLaren
If I read the Tower website description, I would expect a servo with three wires. Because of the very high consumption, the signal and ground wires only are conected to the rx and I would assume that the rx connection must be made before the power supply connections are made to the battery.
At these extremes I think you need to consider the earthing of this lot carefully, high power motor circuits usually get wired to a single earthing point. I'd also worry about lead lengths, lead layout and noise, because I'm not skilled in thiese things but do know they matter when you start "pushing the envelope". Be interested to hear what the expert view is.
Steve
Reply to
Steve W
| At these extremes I think you need to consider the earthing of this | lot carefully, high power motor circuits usually get wired to a | single earthing point.
Earthing doesn't mean much in a R/C plane. The Earth is a few hundred feet thataway :)
If you're talking about everything going through the negative wire, then it might need to be bigger -- but still no bigger than the positive wire, since the current through the signal wire is still negligible in comparison.
| I'd also worry about lead lengths, lead layout and noise, because | I'm not skilled in thiese things but do know they matter when you start | "pushing the envelope". Be interested to hear what the expert view is.
Just use thicker wires and bigger batteries and you'll be fine.
Sure, the servo might use a few amps under load, but that's still nothing compared to the motor on a big electric plane.
Reply to
Doug McLaren
| > | > | > | | > | | > | >According to Tower Hobby, their System 2000 Dual-BB Giant scale Servo | > | >TS-80 comes with 2 (NOT 3 wires). | > | > No, that's not what they say. Not on the web page, anyways. | > | > | >They also say that the third wire is not necessary. | > | > They don't say that either. | > | > | That servo depends on the same electrical connections as any other: power, | > | ground, and control signal (with the standard 1500 us neutral spec as any | > | other servo). | > | > Yup. It just has two sets of power connectors, so it can get more | > power. | > | > The item is actually here -- | > | >
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| > | > ... though to be fair, it does sort of look like, in the picture, that | > the servo only has two wires. But it's hard to tell -- it could just | > be that two of the wires are black, and the third red. | > | > Either way, I'm pretty sure it has the usual three wires. | > | > `Running w/No Load: 700mA' ... wow, that's a lot. Imagine if you | > actually put a load on it! :) | > | > -- | > Doug McLaren, snipped-for-privacy@frenzied.us | > Take everything in stride. Trample anyone who gets in your way. | | " Either way, I'm pretty sure it has the usual three wires." | | Nope, only 2! | | I called Tower Hobby and they confirmed that the middle signal wire is | NOT on a TS-80 or is it necessary. | | EVERYONE thinks otherwise, hence my confusion. | | | If you parallel the 2 wires to the receiver and the battery, I believe | that this comment below would be problematic because the servo would | continuously turn due to the applied DC voltage. | | "That said, because the high power requirement for this servo could | damage | standard receivers (which simply may not have enough metal in the | power path | to the output connectors) the servo must be connected directly to a | power | source (battery) as well as the receiver output." | | How do you connect a servo directly to a battery and not have it turn? | | What am I missing? | |
The three wire servo powered through the receiver always has power supplied to it when the battery switch is turned on.
The difference is this servo is not being powered through the receiver buss which is only thin lands on the rcvr circuit board. The servo doesn't "do" anything until a signal is given to the servo amplifier to move one direction or the other. There has to be a signal lead somewhere.
Reply to
OldPhart
The following Statement by Tower Hobby Rep confirms it is a three wire servo
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Actually a Hitec RCD HS-805BB OEM for Tower Brand but which could have slight differences (as the Tower OEM digitals are not programmable etc) to the HS-805 Specification sheet .pdf = Modifying the internal potentiometer of the TS-80
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Modifying the internal potentiometer of the TS-80 will be of interest to many readers.
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The Negative and Signal leads (Yellow & Black or White & Black) must be used, the red is not used when using a positive bus or separate battery source as is recommended for this servo as current draw exceeds that available from many receivers, especially those with BEC.
Regards Alan T. Alan's Hobby Model & RC FAQ Web Links
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Reply to
A.T.
Mystery solved!!
As always, you guys were correct.
This is the story:
The TS-80 was given to me for a video boat project.
I need a BIG servo to turn steer the air prop and the motor.
The TS-80 was used in a robot as a wheel motor.
The user had wired a black and a red wire directly to the motor terminals.
When I opened it up, I saw only 2 solder points and nothing else.
After you guys convinced me that there really should be 3 wires, and after a call back to Tower Hobbies (Who had the 2 wire photo on their web site), who confirmed the 3 wires, I got serious.
It took me about =BD hour to unsolder the leads and to lift up the circuit board.
Lo and behold! The guy had tucked all the original 3-12" wires and the connector beneath the board.
He had 'floated' the potentiometer away from the shaft key to eliminate any stops.
I put it back together as designed.
FINALLY!!!
Thanks all for your input and for your patience.
BoyntonStu
Reply to
BoyntonStu
No memo - on first and second reading I missed the remaining quoted bit of my followup, and wondered why someone would go through all that trouble when they might as well have replied to the original post ;-)
Cheers
/daytripper
Reply to
daytripper
On Thu, 02 Aug 2007 14:09:10 -0700, BoyntonStu wrote in :
Thanks for coming back with information about what you found.
That's how it looked to me.
Well done!
That sure as heck seems to cover all the bases.
Marty
Reply to
Martin X. Moleski, SJ
:
Thanks,
First, Tower Hobbies NOW agrees that their photo is not correct.
Why/where/how the erroneous photo? Dunno.
Second and really important: The Tower Hobbies person who answered my first call BS'd me into believing that not only was the photo correct, but with a strong and very convincing voice said that the 3rd wire was not needed at all!
I am a newbie, I have never used a servo, I looked inside and I saw only 2 solder points and the 2 wires, I believed Tower Hobbies!
How the heck was I to think that underneath a soldered-in board were 3 additional wires and the connector?
Thumbs down for Tower Hobbies.
Thumbs up for rec.models.rc.air!
BoyntonStu
Reply to
BoyntonStu
On Fri, 03 Aug 2007 05:21:48 -0700, BoyntonStu wrote in :
I wouldn't be too hard on them.
They undoubtedly have experts as expert as anyone anywhere in the RC arena.
But their most expert experts aren't going to be tied down to answering questions at the help desk.
I pity the poor folks in the front line of customer service who are expected to know everything about everything TH sells. It's a daunting task.
Hear, hear! I've been reading it for almost 12 years. Google's archives make it a real treasure trove of information.
Marty
Reply to
Martin X. Moleski, SJ
Correction, HS-805BB specification sheet =
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duplicating pot mod in lieu of above link regretted, regards Alan
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Reply to
A.T.
Now that the smoke and flame has died down-- it is possible to have a two wire servo. Just not without major modification or redesign of the current servos. The problem is that the two wires also carry power to the servo motor. Because of this noise related to the servo motormust be filtered out of any control signal sent down the wires. I always liked the idea of using fiber optics to carry the control signal to the servos instead of a wire. This would allow the receiver and the servo power to be completely independent, and without a common ground. (if needed)
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Reply to
Chuck

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