Servo voltages question

[Gebbly]

I have been reading/watching about battery voltages and matching voltages to the operating voltages of ESCs and motors but started to get a little confused by servos. Most servos I look at seem to be designated as "NiMH" servos which have an operating voltage of 6v or "LiPo" servos which have an operating voltage of 7.4v.

This would make sense to me if a NiMH battery was 6v but there are a lot of 7.2v NiMH batteries. If I were to plug, say, a 9.6v battery into a motor that had an operating voltage of 6v I think it would gradually overheat the motor wouldn't it?

So if I had a setup that uses a NiMH 7.2v battery and match it with an ESC and motor that run with 7.2v but one of these "NiMH" servos with an operating voltage of 6v would it damage or overheat the servo? Or perhaps the ESC would drop down the voltage it passes on to the servo to 6v or something?

I have found a single servo in a single webstore that mentions running at 7.2v here.

[It feels like I'm posting lots of questions on these forums recently but I do try searching the web for answers first honest ]

[sosidge]

Most electric cars will use some kind of BEC (battery eliminator circuit) that steps down the voltage that the receiver and servo sees.

So a typical ESC will take the 7.2V (or whatever) input and step it down to 6V which it sends down the receiver cable. It's this voltage that the servo runs from.

6V is the classic standard (5 cell NiMH/4 cell Alkaline) from the days when receivers and servos were powered by a separate battery pack (still the case for engine powered cars).

7.4V is a newer option based on the higher voltage of a 2s LiPo battery. It means you get a bit more servo performance for free if your servo and receiver can handle it.

7.4V servos will still run on a 6V input. But 6V servos might overheat at 7.4V.

[Gebbly]

Sorry Sosidge, I was with right up until the last sentance.

7 minutes ago, sosidge said:

So a typical ESC will take the 7.2V (or whatever) input and step it down to 6V which it sends down the receiver cable. It's this voltage that the servo runs from.

Great, that makes sense. But then I got lost when you said

7 minutes ago, sosidge said:

But 6V servos might overheat at 7.4V

Wouldnt the ESC step the 7.4v down to 6v to suit the servo as you mentioned?

[sosidge]

2 minutes ago, Gebbly said:

Sorry Sosidge, I was with right up until the last sentance.

Great, that makes sense. But then I got lost when you said

Wouldnt the ESC step the 7.4v down to 6v to suit the servo as you mentioned?

I was using the example where you have chosen to send 7.4v to the receiver.

[Gebbly]

16 minutes ago, sosidge said:

you have chosen to send 7.4v

So when setting everything up I have to set a din switch or something on the ESC to tell it to only pass on 6v to the servo, it doesnt do some sort of auto sensing?

I apologise if this is obvious to everyone else. I seem to have a blind spot here.

[sosidge]

31 minutes ago, Gebbly said:

So when setting everything up I have to set a din switch or something on the ESC to tell it to only pass on 6v to the servo, it doesnt do some sort of auto sensing?

I apologise if this is obvious to everyone else. I seem to have a blind spot here.

Check the ESC specs to see what options you have.

[Jonathon Gillham]

36 minutes ago, Gebbly said:

So when setting everything up I have to set a din switch or something on the ESC to tell it to only pass on 6v to the servo, it doesnt do some sort of auto sensing?

I apologise if this is obvious to everyone else. I seem to have a blind spot here.

Often the ESC will have a programming card which allows you to set the BEC voltage. Older ESC woukd give 4.8v or 6v options, but newer tend to offer 6v or 7.4v. 7.4v is considered high voltage for servos. More volts generally means more torque and faster, so HV servos are 'better'

These are nominal numbers too. A fully charged 2S lipo is around 8.4v but a 7.4v servo would handle this ok. Most nitro cars run the battery straight to the receiver and the 7.4v rated servos and receivers can handle a fully charged 2s lipo fine.

[Gebbly]

Thats brilliant, thanks. I think I've got it now.

[alvinlwh]

IIRC, you are running brushed motor with NiMHs right? Only a few brushed ESC have the BEC voltage setting, those using program cards abd/or PC are generally brushless ESC. 

One brushed ESC that has such a feature is the Bluetooth enabled ISDT ESC70. The BEC can be set from 5.0 to 7.5v, in 0.1v steps. 

[Gebbly]

Yes, I'm preparing to build a GF-01. I am planning on using the motor that came with it (a Tamiya torque tuned) which I believe is brushed and I was going to set it up with a 7.2v NiMH battery (about 5000mAh maybe), a Hobbywing 1080 as suggested on these forums as a reliable ESC and then whatever receiver and servo I could find that would be happy working with those components. For the servo I am just looking for anything waterproof and with metal gear that will be happy plugged into that Hobbywing 1080 powered by 7.2v NiMH.

Alvinlwh, an ESC you can control from your phone via bluetooth? Very cool toy

.....

As I typed the above everyones previous advice all clicked into place, including the fact it is the "BEC" that is controlling the power sent to the servo. Looking at the details of the Hobbywing 1080 on various sites it sounds fairly  programmable so digging I found this which shows all the settings you can adjust on the 1080 and I noticed that you can set the BEC output voltage to either 6v or 7.4v.

Now, thanks to everybody above it all makes sense. I make sure that I alter the settings in the 1080 to set the "BEC Output Voltage" to 6v and then I can use any of the cheaper 6v servos.

Brilliant, thanks everyone!

[alvinlwh]

2 hours ago, Gebbly said:

Alvinlwh, an ESC you can control from your phone via bluetooth? Very cool toy

It is rather cheap too, same price or even cheaper than a 1060.

[Nikko85]

On 6/13/2022 at 2:25 PM, Gebbly said:

Yes, I'm preparing to build a GF-01. I am planning on using the motor that came with it (a Tamiya torque tuned) which I believe is brushed and I was going to set it up with a 7.2v NiMH battery (about 5000mAh maybe), a Hobbywing 1080 as suggested on these forums as a reliable ESC and then whatever receiver and servo I could find that would be happy working with those components. For the servo I am just looking for anything waterproof and with metal gear that will be happy plugged into that Hobbywing 1080 powered by 7.2v NiMH.

Alvinlwh, an ESC you can control from your phone via bluetooth? Very cool toy

.....

As I typed the above everyones previous advice all clicked into place, including the fact it is the "BEC" that is controlling the power sent to the servo. Looking at the details of the Hobbywing 1080 on various sites it sounds fairly  programmable so digging I found this which shows all the settings you can adjust on the 1080 and I noticed that you can set the BEC output voltage to either 6v or 7.4v.

Now, thanks to everybody above it all makes sense. I make sure that I alter the settings in the 1080 to set the "BEC Output Voltage" to 6v and then I can use any of the cheaper 6v servos.

Brilliant, thanks everyone!

I have this exact set up on the GF01s but just with the HW 1060. Personally I think the 1060 is fine with these voltages and power if the torque tuned and so easy to use.

I use an eTronix waterproof 15 kg servo as it is sturdy and strong. No issues at all and works perfect on NiMH 7.2v. On my heavy dump I run two servos, one additional servo for the bed mechanism. Zero issues. 

 

 

 

 

 

[Gebbly]

Ah yes I read your thread about the truck with the tipping bed, very cool. I'll checkout that eTronix servo. Its always reassuring if someone has already used a component and proved it works.