kiyoung

Hi,

I like the spec of 7940 and 7950. Can I use them without a voltage regulator?
When are they going to released?

Thank you very much in advance

MikeMayberry

My Feedback: (1)

Yes, as seen here: http://www.hitecrcd.com/servos/show?name=HS-7950TH

Due: May/June

Mike.

I Buy Houses

That is Awesome!
Does Hitec have any smaller servos that can run on 7.4V. So you don't have to spend $150 on a throttle and choke servo?

MikeMayberry

My Feedback: (1)

The 7954SH will be the least expensive @ $109.99. It's essentially the same exact servo as the current 7955TG but with Steel gears. Yes, the 7955TG can handle 7.4v too!

Mike.

I Buy Houses

Hi Mike,
Thanks so much! That will end up being some expensive throttle and choke servos for planes. I'll consider it

Spooker1

Hi,

Just to understand it right, the HS-7955TG is cable of taking 7,4v from a LiPo? If yes, why isn't it in the spec? And how many oz in does it then take with 7,4v?
I probably recieve my 7955's tomorow, and I would hate to connect a 7,4 LiPo, and the see it "explode". I thougth I had to use a voltage limiter.

Best regards and thx.

tohm

We have tested the HS-7955 with 7.4V lipo packs and have not had any adverse problems. Many of our team drivers/pilots have been doing this for some time now. The spec sheets will probably not change, as they were written in 2007, way before we did actual testing with the higher voltages.

At 7.4V, the torque is 387oz/in and the speed is .13sec.

Tony Ohm
Hitec/Multiplex USA

Spooker1

Thx tohm.

Just the answer I was hoping for. I'll be the first danish driver with a LiPo setup for a 1:5 touringcar, with two 7955 and one 7950 i'll guess.
Just have to wait until the 7950 is on the market though..... Makes my dream come true ;o)

Best regards.

kiyoung

Hi, spooker1

I have the same idea. I am planning to install 4 7940 servos in my HARM SX3 with Ripo.
2 for steering, 1 for throttle, 1 for front brake.
I already bought carbon radio plate from HARM four month ago.

But, when they are going to release 7940 servos?

Spooker1

I have discovered a minor issue.

I´m gonna use 2 Hitec 7955 and 1 Hitec 7950 in my 1:5 car. The receiver im using (Futaba603FS) does only operate on 6v, but I'm interested in using a 7,4v LiPo for the servoes. Is there any way I can support my servoes with 7,4v and at the same time reduce voltage to 6v on the reciever?

Best regards

kiyoung

I will try a voltage regulator to reduce a voltage to a receiver. Maybe it works, maybe not. I am not sure.
If above method is unsuccessful, I will use Lipo without a voltage regulator. Some people in Korea use Lipo without a voltage regulator.
Yes, it is risky.

If you have another idea, please let me know.

Best regards

Spooker1

By using a voltage regulator, Isee a limitation in amp when operation with 3 servo´s. So far I have a regulator om 7A, but I think it´s insufficient - or what?

Then I´d rather use a 6v NiMhbatterypack.....

Best regards.

skubacb

On Hitec's site only the servos ending with a TH are rated for 2 cell lipo. It might be nice if Hitec would mention in the specs that the HS-7955TG or others can take a 2 cell lipo.

BTW what is the torque/speed of the 7955 with the higher voltage. I would expect it to be higher than its 6 volt rating.

kiyoung

Hi,

I have used 7940 servos for more than 6 months with lipo battery. They are extremly fast.
I don't use regulator for receivers. My receiver are Futaba 603fs and 604fs. The receivers are working just fine with regulator.

A.T.

<dt>Servo - Operating Voltage Range - usuage with Lipol & A123 batteries. </dt><dt>Servo - Operating Voltage Range - Hitec Pre-HV Servos useable with unregulated 2S Lipo </dt><dt>Servo - FAQ : Torque Tester - DIY
and more at
Alan's Hobby, Model & RC FAQ Web Links</dt>

Regards
Alan T

skubacb

Interesting A.T. but still doesn't quite answer the question.

I would like Hitec to let us know. Again on the website only TH are rated for a 2 cell lipo.

Don't get me wrong. I think Hitec produces the best servos and their service is outstanding. Futaba's service is not even in the same league with Hitec.

Brendan Lugo

The 7955TG was only rated for 6 volts and so thats what will be stated on the web site. Off the record, we have used it in 7.4 volt (2s) setups and have not had any issues with it in doing so. So if you have those servos and need to run them at the higher voltage, there is not a problem in doing so but the specs on the web site will remain as they are since it was only designed to be run with a max 6 volt (5 cell) setup.

skubacb

Ok,
I noted what was being said on this site versus the Hitec site. So that is now clear.

BTW, I would love to see Hitec produce a servo with the same torque as the Futaba S3114 (24 oz/in). At the AMA show Hitec was telling me that the HS-55 (18 oz/in) was good enough for my foamies. The HS-55 has .333 less torque than the S3114. The other Hitec choices in that area even the 5056MG at a whopping $42 has less torque. But it is fast.

Bottom line is I prefer the Hitec servos but in the case of my foamies I am using the S3114 unless it is an indoor or very light foamie. Everyone else in our club of about $250, that flies something like the Charger RC CR1/Fusion/CR260, are using S3114s since it meets the torque and price point they want. We can feel that the 55 just can't move the controls adequately.

If I can get a Hitec servo equal to the S3114 then I can stick with Hitec.

FreedomFlier

My Feedback: (8)

Background and Problem Statement:

Installation of this system is in a Chief Aircraft purchased Pilot RC Sbach 342 with a DA120 install. The servo configuration is 5 HS-7950TH, one for each control surface, and one HS-7954TH for the throttle. Batteries include two Li-Ion 2S 5200 mAh packs. Initially the RX of choice for this installation was the JR R922 50-Amp Powersafe receiver. I first installed the elevator servos and throttle servos, and then left the aileron and rudder servos uninstalled but plugged into the RX in the plane. The aileron servos are installed on 24” extensions, and the Rudder, and two elevator servos are terminated to 36” extensions. All extensions are β€œheavy” 22 gauge units. I did not want to install the rudder servo at this point, since I had not checked CG with this configuration. So the aileron and rudder servos were on the test bench next to the plane, but not installed.

After installing this system in the mocked up configuration, on power up and cycling the gimbals a few times, I noticed immediately that the tail servos were erratic in ether direction. They would jump 5-10 degrees in ether direction. The Ailerons were not as jumpy, and would marginally glitch, but not as bad. The throttle servo on 18” extension was stable and accurate and I did not notice any jumping. Obviously, this is not an airworthy configuration.

Youtube video link below:

http://www.youtube.com/watch?v=Ubu6wPKPi_Q

After disconnecting all of the extensions, and plugging into the receiver directly to isolate possible connector attenuation as a source of the problem. I powered up the system, synced to the TX DSM2 bound signal, and the servos moved graceful and accurately. Hitec told me i had a voltage drop on the signal across teh extention... Now in attempt to isolate the source of the problem(s), I omitted the JR R922 from the system, and replaced it with a Spektrum AR7000 receiver without regulators. It’s specification sheet is published to have a input voltage of 3.5v to 9.6v. After installing the receiver, including the extensions, the jittery-jolting-inconsistently-radical behavior was minimal on the 36” leads only! (95% glitch free) When installing a 6.0v Fromco regulator, these ill behaviors disappeared and the system seems to run healthy. I then decided I wanted to measure the voltage of the signal from the RX to teh servos, and attempt to qualtify how much of signal was degrated across teh extention.

Now, connecting HS-5955TH servos to the 36" extentions, JR R922 RX, they work perfect...??? I know they are not reated for > 6.0 volts, but I needed to know how they work with the JR setup.

Test and Measurement instrumentation modules:

Servo Lead β€œBreakout box” or modified 22g 6” jumper
General Purpose Digital Multi-meter
Tektronix 2225 Oscilloscope

Test Case Scenarios:

1. JR R922 Power Saver Receiver, no regulators

Measure Battery output voltage __8.14v_
Measure output power of RX Voltage _8.10v__
Measure signal voltage at RX with Oscilloscope 3.5v___
Measure output of power Voltage with 36” _8.10v__
Measure signal voltage at 36” ext w/Oscilloscope _3.5v__
Note drop in voltage with 36” extensions. ~0 ???

* Very erratic servo behavior!

2. Spektrum AR7000 Receiver, no regulator

Measure Battery output voltage __8.14v_
Measure output power of RX Voltage _~8.10v__
Measure signal voltage at RX with Oscilloscope 3.5v___
Measure output of RX Voltage with 36” _8.10v__
Measure signal voltage at 36” ext w/Oscilloscope _3.5v__
Note drop in voltage with 36” extensions. ~0

*Remarkably improved performance over the JR RX.

3. Spektrum AR7000 Receiver, Fromco 6v regulator, set to 6.00v

Measure Battery output voltage __6.10v_
Measure output power of RX Voltage _6.10v__
Measure signal voltage at RX with Oscilloscope ~3.45v___
Measure output of power Voltage with 36” _6.10v__
Measure signal voltage at 36” ext w/Oscilloscope _~3.45v__

Note drop in voltage with 36” extensions. ~0

*Silky smooth modulation and crisp servo response.

Conclusion(s) and remarks:

Is the Signal to Power level ratio detection threshold in the servo to high? I noticed that regardless of what input voltage, or extension length that the signal voltage was always approximately 3.5vDC. What is the signal detection threshold for Hitec servos? What about JR Hi-Voltage servos? Below is an illustration barrowed from Servo city that illustrates the servo PWM signal. One could also argue that the signal to power ratio is too low from the receiver if running higher input voltages. An example would be the transition manufactures made to support 6.0vDC from 4.8v, there were issues with some models of receivers that would output a peak of 2.7vDC for the signal which was fine for 4.8vDC packs, but would cause problem with a fully charged 6.0 battery pack. As the charge wore off, the system would stabilize and become less erratic.

http://www.servocity.com/html/booste...xtensions.html

The other observation, is that there was negligible (as predicted) reduction on the signal voltage using a 36” extension per the oscilloscope readiness. (I measured .3 Ohms across the 36” extensions) I took pictures of each test scenario , but they all yield basically the same 3.459ish signal. I was surprised to see this and initially expecting to see a more proportion rise in signal voltage, relative to the input power. But on the other hand it makes sense to move the hefty juice to the muscle bearing the burden of the power leads driving the motor.

Other comments>>

If I run my batteries through a switching harness, then into the R922 w/servos extentions, gliching is minimal. measured voltages are the same at RX and end of ext.

I used the HS-21 and changing deadband and resolutiuon does nothing to fix the glitching.

I'll post more as I learn more from JR/Hitec. For now I'll run the AR7000 and 6V reg.

Once again, the old 5955TH servos work fine with the JR reciver.

Would somebody from Hitec pLease help! I spent good $$ going to "High Voltage" and now I'm back running a 6.0 setup.

Giln

Good post FreedomFlier - thank you.
I look forward to an update.

I am buildng a 100cc Sbach.
Plan 5 x HS7950H, Fromeco a123's unregulated through a R1222 50-Amp Powersafe receiver.
You can see why I have an interest.

Regards
Gil

Karman

Hi,

we often have "interferance" on helicopters when the servo wires are neatly coiled up to the gyro. My theory behind this is the EMF is amplified due to coils and gyro picking this up.

what i'm now wondering is, when you up the voltage on the system, your EMF will go up, and might explain why the "old" rx is picking up more noise, where "newer" rx is not. (better shielding bla bla bla).

have you tried single servo and tested in different locations from the rx? also did you try moving battery packs around?

the fact that its better with switch might be that it acts as "suppressor".

just few thought you might try... my bet is still on increased EMF due to higher voltages

L: