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TBM 8711 vs 5955 servo test...

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Old 06-02-2007, 09:39 AM
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Default TBM 8711 vs 5955 servo test...

Just wondering what you guys thing about the servo test TBM did on the 8711 vs the 5955.

I was pretty surprised that the servos dropped off so much after only 60 seconds of "intermittent use" and also surprised that the 8711 gets up to 120 degrees.. no wonder they put a heat sink on the thing.

40% drop off on the 5955 was a shocker also, maybe they (whoever they is) need to change the way servo torque is rated to power available after 60 seconds of intermittent use.

I was also quite surprised that there was such a big difference between ten 6" extensions verses the ten 48" extensions, I was always under the impression that the voltage drop in our particular applications was due to the connectors, now it is obvious that wire length has a lot to do with it as well. I know you probably wont ever use ten 48" extensions on one servo but it's nice to know information.
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Old 06-02-2007, 09:48 AM
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Default RE: TBM 8711 vs 5955 servo test...

I read that, too, Nick, and was only a *little* surprised at the current load, frankly. These honkin' powerful servos that we are "needing" come at a power price, for sure. I think it also confirms the connectors and wire gauge really *do* make a significant difference when loaded with high current draw. I run only 22 gauge wiring, and try to stay under 30" extensions, minimize connectors, etc., but maybe we are at a crossroads of connector and wire design parameters, as the engineers among us have prophesied for so long.

Tough part will be for the manf. to re-engineer the RX's for higher current capability through the power buss.

I appreciated TBM doing that testing.....

ORIGINAL: camss69

Just wondering what you guys thing about the servo test TBM did on the 8711 vs the 5955.

I was pretty surprised that the servos dropped off so much after only 60 seconds of "intermittent use" and also surprised that the 8711 gets up to 120 degrees.. no wonder they put a heat sink on the thing.

40% drop off on the 5955 was a shocker also, maybe they (whoever they is) need to change the way servo torque is rated to power available after 60 seconds of intermittent use.

I was also quite surprised that there was such a big difference between ten 6" extensions verses the ten 48" extensions, I was always under the impression that the voltage drop in our particular applications was due to the connectors, now it is obvious that wire length has a lot to do with it as well. I know you probably wont ever use ten 48" extensions on one servo but it's nice to know information.
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Old 06-02-2007, 10:14 AM
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Default RE: TBM 8711 vs 5955 servo test...

Hmm...

It seems to me from what I've seen posted on the various manufacturer's support forums that the limiting factor right now is not the rx power buss since most are saying that the rx can handle substantially more current that we normally use.

I thought the biggest hangup right now is the connectors and those hollow pins used in them, then the wire gauge/length issue?
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Old 06-02-2007, 10:16 AM
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Default RE: TBM 8711 vs 5955 servo test...

Yes - but to revamp the connectors/plugs, RX's will have to be re-designed. The actual PCB in the Spektrum and JR Rx's have been stated by manufacturers to be capable of the current loads. If the PCB foil can handle it, but the connector pin/socket cannot, we're back to "weak link" mode.

ORIGINAL: Zeeb

Hmm...

It seems to me from what I've seen posted on the various manufacturer's support forums that the limiting factor right now is not the rx power buss since most are saying that the rx can handle substantially more current that we normally use.

I thought the biggest hangup right now is the connectors and those hollow pins used in them, then the wire gauge/length issue?
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Old 06-02-2007, 08:18 PM
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Default RE: TBM 8711 vs 5955 servo test...

I was pretty surprised that the servos dropped off so much after only 60 seconds of "intermittent use" and also surprised that the 8711 gets up to 120 degrees.. no wonder they put a heat sink on the thing.
were does this scoop come from?
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Old 06-02-2007, 09:24 PM
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Default RE: TBM 8711 vs 5955 servo test...

ORIGINAL: krayzc-RCU

I was pretty surprised that the servos dropped off so much after only 60 seconds of "intermittent use" and also surprised that the 8711 gets up to 120 degrees.. no wonder they put a heat sink on the thing.
were does this scoop come from?
undefined

Troy Built Models in the servo section they have their comparison and test procedures.


You know what has been getting me lately is why do we have voltage regulators with giant heat sinks built in, some even with Fans, and yet the RX which is capable of what 30 amps current has none? ALL that current is passing through the RX and it doesn't get hot, weird. If i feel my regs right after a flight they are pretty toasty...

I made sure to get 60+ seconds of Intermittent use on my single 8711 rudder servo today and I don't know if it was just because I was looking for it, but it did seem that knife edge stuff was easier at first and then I lost power.. I have a second 8711 and an already programmed matchbox sitting in the toolbox, I'm going to drop it in and see if I notice a difference.







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Old 06-02-2007, 10:04 PM
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Default RE: TBM 8711 vs 5955 servo test...

wow interesting scoop u all are providing
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Old 06-03-2007, 10:06 AM
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Default RE: TBM 8711 vs 5955 servo test...

In the static load testing I did two years ago I found that temperature rise limits the output of the servo very quickly. You have to reduce the load quickly or you might damage the servo. The 8611A would last only about 15 seconds at full load before the motor burned out. The 5955 would last a lot longer but it would only produce about 70% of the torque Hitec claimed. Since I am told they used the same motor, I think Hitec found that out and limited the output of the amplifier to prevent this.
I would be interested in a load test of the 8711.
I also found that you cannot use the high torque of the 8611A anyway. It requires such a high error signal to get it that it is unusable. Not so of the 5955.
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Old 06-03-2007, 10:11 AM
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Default RE: TBM 8711 vs 5955 servo test...


ORIGINAL: camss69



You know what has been getting me lately is why do we have voltage regulators with giant heat sinks built in, some even with Fans, and yet the RX which is capable of what 30 amps current has none? ALL that current is passing through the RX and it doesn't get hot, weird. If i feel my regs right after a flight they are pretty toasty...


Because the regulator is stepping a higher voltage down to a lower voltage, the only way it does this is by releasing heat....
(hence the BEC on ESC's get so hot)
while the RX is just using the voltage that it is provided... it doesn't do any regulation
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Old 06-03-2007, 10:54 AM
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Default RE: TBM 8711 vs 5955 servo test...

Slowly the sun comes up---
increased power from servos comes from increased power delivered to them --
some points to ponder .
The LiIon batts which supply power thru regulators are an assembly of bottlenecks
a resistive regulator gets hot - and will fail and will crash you -
solution - shi-t can the setup .
use cells which put out all the power YOUR servos ask for. They do exist.
Connectors we use, were designed for far , far lower loads than we now have available . (they heat at 4 amp loads ).
solution- parallel paths -at least until better connectors and busses become available
The easy setup would be for someone to make n market a small piggyback buss/signal bar which pushes onto existing RX buss - and has 8 amp flow type connectors . Yes I know about the power distributing units on the market.
wiring and the new bus would of course have to be a mating set. a simple setup.
A small mfg could do this -basically a battery to servo system which is double present setups.
anything under 33% has no need for this kind of a fix but 40+ % stuf could use it.
Ben thar-------
One more thing-- good switching regulators don't heat like the cheapos - The present BECs in ESC s -are behind the curve on the higher power motors using higher voltages- get an external BEC- Dimension Eng has some dandy ones .
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Old 06-03-2007, 10:57 AM
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Default RE: TBM 8711 vs 5955 servo test...

The receiver does in fact have a built in regulator. But since it only uses s few milliamps its not going to get hot.
You would be better off to use a voltage the servos are designed for and get rid of that regulator. It just wastes power and is a source of trouble. In fact all of the failure modes of that regulator would mean the loss of your aircraft.
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Old 06-03-2007, 11:03 AM
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Default RE: TBM 8711 vs 5955 servo test...


ORIGINAL: dick Hanson

Slowly the sun comes up---
increased power from servos comes from increased power delivered to them --
some points to ponder .
The LiIon batts which supply power thru regulators are an assembly of bottlenecks
a resistive regulator gets hot - and will fail and will crash you -
solution - shi-t can the setup .
use cells which put out all the power YOUR servos ask for. They do exist.
Connectors we used were designed for far far lower loads than we now have available . (they heat at 4 amp loads ).
solution- parallel paths -at least until better connectors and busses become available
The easy setup would be for someone to make n market a small piggyback buss/signal bar which pushes onto existing RX buss - and has 8 amp flow type connectors .
wiring and the new bus would of course have to be a mating set.
A small mfg could do this -basically a battery to servo system which is double present setups.
anything under 33% has no need for this kind of a fix but 40+ % stuf could use it.
Ben thar-------
One more thing good switching regulators don't heat like the cheapos - The present BECs in ESC s -eare behind th curve on th higher power motors - get an external BEC- Dimension Eng has some dandy ones .
undefined

Fromeco makes a regulator with up to 3 JR type connectors to go directly into the RX. I'm using two regs with two connectors each for a total of 4 to the RX. If you read the review power supplied to the servos was not the problem, it was load on the servos for an extended amount of time (60 seconds) and also note that this is not in a stalled condition but in a simulated normal use condition.
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Old 06-03-2007, 11:11 AM
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Default RE: TBM 8711 vs 5955 servo test...

Frankly I see no need for regulated batteries --
what the simple LiIons now available cant handle --th e123 cells can -
as for the weight difference - let's get serious
unles you feel it necessay to pack around a weekends worth of battery power in one charge - why not have a simple monitor and recharge setup which you use as you refuel ?
either the 123 or the new NiMh cn be very quickly topped off -
or is everyone using 128 oz tanks?
I am sur this falls on many deaf ears who are sold on the current (drum roll), electrifying setups that cost an arm and a leg (rimshot).
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Old 06-03-2007, 11:19 AM
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Default RE: TBM 8711 vs 5955 servo test...

to do the static load test does the servo hold the postion for over a minute without being moved?
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Old 06-03-2007, 11:30 AM
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Default RE: TBM 8711 vs 5955 servo test...

That is a NASTY way to test --in actual practice it is not going to happen.
Personally I use setups which simply can't stall ANY servo on th model . to do so is folly by golly.
I use multipe servos on ailerons and max out servo rotatiuon to surface movement -always
my 33% Extra has 4, 55 in ounce 811 servos operating on 3 123 cells and the thing has extremely fast roll speed .
for th elevators -you need more but never do a setup which stalls the servos under flight loads
ad servos add higher voltage but don't stall the servos.
hysterisis is not a medical procedure - it is a case whre the servo position is not balanced to the input and if it is excessive - it will smoke em
any of em
all of em
anytime
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Old 06-03-2007, 11:48 AM
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Default RE: TBM 8711 vs 5955 servo test...

Dick,

Have to admit it you OUTDID yourself with this one----{Quote} hysterisis is not a medical procedure

Bravo (which happens to be the positive statement vs Oh Sh** !)
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Old 06-03-2007, 01:18 PM
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Default RE: TBM 8711 vs 5955 servo test...


ORIGINAL: dick Hanson

That is a NASTY way to test --in actual practice it is not going to happen.
Personally I use setups which simply can't stall ANY servo on th model . to do so is folly by golly.
I use multipe servos on ailerons and max out servo rotatiuon to surface movement -always
my 33% Extra has 4, 55 in ounce 811 servos operating on 3 123 cells and the thing has extremely fast roll speed .
for th elevators -you need more but never do a setup which stalls the servos under flight loads
ad servos add higher voltage but don't stall the servos.
hysterisis is not a medical procedure - it is a case whre the servo position is not balanced to the input and if it is excessive - it will smoke em
any of em
all of em
anytime
undefined

You are right in actual practice the servo is never stalled. Well at least almost never.
But then that is the way the specs are stated. The maximum torque is at the maximum stalled condition. The maximum stalled condition is thus useless except for comparison of the servos.
The maximum stalled condition will burn out most servos if kept there long enough but some burn out much quicker than others. A three pole servo will last much longer because of the built in heat sink in the motor winding. Some three pole servos might not burn out at all depending in the capability of the amplifier. BTW hysterisis has nothing to do with it.
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Old 06-03-2007, 02:34 PM
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Default RE: TBM 8711 vs 5955 servo test...

hold on -- I was describing the situation where the servo is commanded to be in a given position but the servo load prevents that from occurring.
What do you call that?
I see the difference in commanded position - to balanced position -as hysteresis .
No so?
What is proper term?
BTW- if you want to check out a servo I really like -- check out the JRSport 126 -a 3 pole , 140 in ounce, all metal gear train servo.
I use these with my 123 two cell packs on elevators on my 33%Edges they are -in my book - very good.
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Old 06-03-2007, 04:47 PM
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Default RE: TBM 8711 vs 5955 servo test...

Consider a servo with a constant load well within its capability.The load curve when traveling in one direction would be displaced from the load curve when the servo traveled in the other direction dependant on the error in its position caused by the deadband at that load. That is the hysteresis loop.
See an electronic text on magnetism. Hysteresis is explained there as caused by the set taken by the magnetic material that must be overcome when the load is reversed. That is similar to what we call deadband.
What you call the difference between the servo actual position and its commanded position? I don't know. I call it the error signal. It is dependant on the load applied.
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Old 06-03-2007, 05:04 PM
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Default RE: TBM 8711 vs 5955 servo test...

semantics -- in common everyday English- hysteresis means the same thing as what ERROR means in electronics.
You can see a general definition in Wilkapedia.
on another note - I just put a hatch on an electric model, using rare earth magnets instead of screws. 196 dia. and incredibly strong. In reading the specs -I was taken waaay back to terms I have almost forgotten-Gauss- (residual induction)--Orsteads intrinsic coercive force. Magnets are Neodymium-Iron-Boron
we call em "strong little buggers" -
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Old 06-03-2007, 10:22 PM
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Default RE: TBM 8711 vs 5955 servo test...

Here is an explaination of hysteresis:

http://www.aacg.bham.ac.uk/magnetic_...hysteresis.htm

Let me know when you get it figured out.

Then you can tell me.
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Old 06-03-2007, 10:37 PM
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Default RE: TBM 8711 vs 5955 servo test...

Yes the technical uses of the word hysteresis, are quite extensive and used in many tech fields..
for the sake of addressing a general audience -I simply used the word in it's broad context.

From Wikipedia, the free encyclopedia

Hysteresis is a property of systems (usually physical systems) that do not instantly react to the forces applied to them, but react slowly, or do not return completely to their original state. The state of such a system depends on its immediate history. For example, if you push on a piece of putty it will assume a new shape, and when you remove your hand it will not return to its original shape, or at least not immediately and not entirely. The term derives from an ancient Greek word υστ*ρησις, meaning 'deficiency'. The term was coined by Sir James Alfred Ewing.

A high power drain occurs when the servo can't (or has not) reach command position.
that is " hysteresis" as the response is not completed.
A high power drain also occurs when an outside force tries to move servo from it's commanded position.
This is easily tested by any user - if a small v meter LCD type is inserted in the system.
I appreciate the tech explanation but the modelling audience really responds best to explanations which are pretty straight forward and easily applied and understood.
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Old 06-04-2007, 09:58 AM
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Default RE: TBM 8711 vs 5955 servo test...

Dick,

The purpose of the thread was about the performance of the servos, not what we choose to power them with, obviously that is an entirely different conversation.

I agree the power needs to be available for the servo to perform, in this case the power is available and it appears performance drops off anyway. If you read the test, they are testing for moving torque not stalled torque, the servo is not in a stalled condition and still performance drops off.
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Old 06-04-2007, 11:24 AM
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Default RE: TBM 8711 vs 5955 servo test...

I appreciate your asessment.
I don't like the idea of regs n LiIon's - anyones.
nothing personal at all .
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Old 06-04-2007, 11:27 AM
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Default RE: TBM 8711 vs 5955 servo test...


ORIGINAL: dick Hanson

Yes the technical uses of the word hysteresis, are quite extensive and used in many tech fields..
for the sake of addressing a general audience -I simply used the word in it's broad context.

From Wikipedia, the free encyclopedia

Hysteresis is a property of systems (usually physical systems) that do not instantly react to the forces applied to them, but react slowly, or do not return completely to their original state. The state of such a system depends on its immediate history. For example, if you push on a piece of putty it will assume a new shape, and when you remove your hand it will not return to its original shape, or at least not immediately and not entirely. The term derives from an ancient Greek word υστ*ρησις, meaning 'deficiency'. The term was coined by Sir James Alfred Ewing.

A high power drain occurs when the servo can't (or has not) reach command position.
that is " hysteresis" as the response is not completed.
A high power drain also occurs when an outside force tries to move servo from it's commanded position.
This is easily tested by any user - if a small v meter LCD type is inserted in the system.
I appreciate the tech explanation but the modelling audience really responds best to explanations which are pretty straight forward and easily applied and understood.
But the hysteresis does not cause the power drain. The load on the servo causes the power drain. You may call the displacement from the commanded position hysteresis but I don't. Hysteresis to me is a fixed displacement caused by the built in characteristics of the material and will occur independent of the load applied and will not cause an increase of the power drain.

On another subject.
I find it interesting that TBM found that most of the servos do not produce the torque the manufacturers claim. They found that the 5955 will produce only about 250 oz-in on 6V. Nowhere near the 333 Hitec claims. This is the same value that I found for the 5955 when I tested it two years ago. TBM says the manufacturers are specifying holding power not ultimate torque. If that is the case I can make a servo with infinite torque. Just replace the gear train with a worm gear or a lead screw
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