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Old 10-28-2014, 05:59 AM   #1
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Default HV Servos - who's running one in a TC

There seems to be a plethora of HV servos coming onto the market, with most of the major brands - and even the smaller specialised ones - coming on board with a low profile offering with typical TC specs;



Standard footprint
25mm ish height
<0.10 60 deg (most well under when on 7.4v)
>7kg torque (most well over when on 7.4v!)

But how are they being powered?

I'm not aware of any top end ESCs with more than a 6V BEC, so to take advantage of the HV specs, would need either direct wiring to lipo, a dedicated RX battery (and a receiver that can handle HV) or a 7.4v external BEC

The former leaves you open to a servo that changes pace as the race goes on and voltage drops from full charge 8.4V to ~7.6V (or what ever you see after your runs) and latter two mean added weight & complexity, plus the possibility of the BEC wiggling out under acceleration and high motor current draw when voltage can drop sharply.

I use HV servos in my 5th scale with a dedicated receiver pack wired direct to them and it works really well - I barely seen 0.1-0.2V drop over a 20min run, so no performance drop off noticed.

Surely someone is using one?
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Old 10-28-2014, 07:42 AM   #2
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Quote:
Originally Posted by cplus View Post
There seems to be a plethora of HV servos coming onto the market, with most of the major brands - and even the smaller specialised ones - coming on board with a low profile offering with typical TC specs;



Standard footprint
25mm ish height
<0.10 60 deg (most well under when on 7.4v)
>7kg torque (most well over when on 7.4v!)

But how are they being powered?

I'm not aware of any top end ESCs with more than a 6V BEC, so to take advantage of the HV specs, would need either direct wiring to lipo, a dedicated RX battery (and a receiver that can handle HV) or a 7.4v external BEC

The former leaves you open to a servo that changes pace as the race goes on and voltage drops from full charge 8.4V to ~7.6V (or what ever you see after your runs) and latter two mean added weight & complexity, plus the possibility of the BEC wiggling out under acceleration and high motor current draw when voltage can drop sharply.

I use HV servos in my 5th scale with a dedicated receiver pack wired direct to them and it works really well - I barely seen 0.1-0.2V drop over a 20min run, so no performance drop off noticed.

Surely someone is using one?
Those specs aren't that impressive, even for 6V

I think most high voltage servo's are designed to be used in nitro vehicles where a lipo receiver pack etc is used.

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Old 10-28-2014, 09:39 AM   #3
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I use a new brand.
Power star PM-1610. Brushless, full metal case.
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Old 10-28-2014, 09:48 AM   #4
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I have that actual Futaba servo in my electric tc.

Its great, quite similar to a 551, and come nitro season, I can run lipo rx packs on them.
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Old 10-28-2014, 09:54 AM   #5
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Tekin RSX ESC have adjustable BEC voltage to 7.4V

Martin Paradis
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Old 10-28-2014, 10:04 AM   #6
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Most of the time the + wire of the servo can be re-routed directly to the battery.

But fast 6v servo's can be found with fast speeds up to 0.05sec so there is no need for a HV servo.
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Old 10-28-2014, 11:25 AM   #7
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The only logic behind a HV low profile servo in a tc, is that you will not have to buy another servo if you decide to put it in a nitro car that runs on a 7.4volt lipo... The protek 160SS is the best out there for the price....lol....
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Old 10-28-2014, 02:04 PM   #8
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Quote:
Originally Posted by Skiddins View Post
Those specs aren't that impressive, even for 6V
Sorry, misleading, I was merely quoting "typical" minimum TC specs, not the specs of that servo in particular!

Quote:
Originally Posted by Skiddins View Post
I think most high voltage servo's are designed to be used in nitro vehicles where a lipo receiver pack etc is used.

Skiddins
I think you are right for the moment. Means they can be used for either. But if you have one and get get more performance at higher voltage, surely would look to take advantage at some stage?

Quote:
Originally Posted by Ho1aw View Post
I use a new brand.
Power star PM-1610. Brushless, full metal case.
And how have you wired it?

Quote:
Originally Posted by R3VoLuTiOn View Post
I have that actual Futaba servo in my electric tc.

Its great, quite similar to a 551, and come nitro season, I can run lipo rx packs on them.
Yep, seems very similar specs to (my) 551, just more torque if you run it at HV

Quote:
Originally Posted by rhodopsine View Post
Tekin RSX ESC have adjustable BEC voltage to 7.4V

Martin Paradis
Ah, there we go, they are coming. I think this will start to be more common....

Quote:
Originally Posted by Roelof View Post
Most of the time the + wire of the servo can be re-routed directly to the battery.
Yep, you can do that, but servo performance - and likely your driving lines - will change dramatically from start to end of the run as the voltage of your main pack drops. That would be crap.

Quote:
Originally Posted by Roelof View Post
But fast 6v servo's can be found with fast speeds up to 0.05sec so there is no need for a HV servo.
If a servo can make the same speed, have more torque, but be more reliable, fit in a smaller, lighter case and use less power - would you consider it?

Oh, but it has to run at 7.4V......

Quote:
Originally Posted by bertrandsv87 View Post
The only logic behind a HV low profile servo in a tc, is that you will not have to buy another servo if you decide to put it in a nitro car that runs on a 7.4volt lipo... The protek 160SS is the best out there for the price....lol....
"Only" logic to you maybe.

Get used to all the big brands only having HV options at the top end of their ranges.

"Best" is also very subjective. On paper is one thing. Real world is often another.
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Old 10-28-2014, 04:04 PM   #9
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Quote:
Originally Posted by cplus View Post
If a servo can make the same speed, have more torque, but be more reliable, fit in a smaller, lighter case and use less power - would you consider it?

Oh, but it has to run at 7.4V......
Todays needed torque is highly overrated (in every class). I do run a stock S3001 on my touring. OK, it can be faster but it is not needed on outdoor tracks. The 3kg torque is enough. The 6v/0.05sec spec servo's do have 4 or 5kg torque, that is more than enough.
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