Direct power servo experiment

[Trucking in space]

So, my budget Yipin 70kg servo run at 7.4 volts is struggling. Under 50% throttle and above the servo has difficulty steering the truck.
At 8.4v BEC, the servo is draining the battery a lot. It is not very efficient.
I am already running an 8200 mah 6s pack, which is the largest I can fit. I had to cut the battery tray already.
So, I would like less battery drain and more torque.
Solution (?) a direct power servo. I ordered an AGF A75BUMW 62kg 16.8 volt servo.
This is my first try with a direct power high voltage servo.
At 11.1 volts, it should output 48kg at 0.125 seconds response time. I may experiment with higher voltages once I work out a better power input. The stock servo has a single jst plug, which I am very skeptical of it being able to draw 12+ volts without melting.
I will power the servo with a 2000 mah 3s lipo. The servo has a second cable for the receiver that will connect only to the signal and ground wires.
Dan B from the Arrma forums is advising me.
I will post update after I set things up. If things look exciting I will post a video for demonstration purposes.

 

[Horatio]

Personally, I find such high torque/voltage servos an absurdity on a 1/8th rig - even one with a 6S battery to run from.

I suppose the servo would be able to draw much more power directly with an XT60 or XT90 - 4-6S.

But - wouldn't it be easier to just select a servo with torque oriented gearing rather than speed? My 45kg servo responds 60°/0.08sec. I don't run it at 8.4v though - it's perfect on 6v and runs well within it's comfort zone.

I might add, that unless the servo is operating through an uprated servo saver spring, no amount of extra current draw will result in more force applied at the steerable wheels.

The Savage I have runs 40 series wheels/tyres running a 13kg servo through an uprated MP steering rack/servo saver. I raced it on this setup and the steering was excellent - even by buggy standards.

The XT8 runs Protek 170 SBL servo for steering - 32kg 60°/0.09 secs @ 6V. It's an awesome servo with excellent centering. If I really felt the need for more, I could run a lighter 2S lipo and regulate the voltage to the receiver.

Most of my nice Futaba FASST receivers are like unicorns now, but don't like higher than 6v.

A decent servo will provide you exactly what you need plugged into your receiver.

 

[Nelson.81]

So, my budget Yipin 70kg servo run at 7.4 volts is struggling. Under 50% throttle and above the servo has difficulty steering the truck.
At 8.4v BEC, the servo is draining the battery a lot. It is not very efficient.
I am already running an 8200 mah 6s pack, which is the largest I can fit. I had to cut the battery tray already.
So, I would like less battery drain and more torque.
Solution (?) a direct power servo. I ordered an AGF A75BUMW 62kg 16.8 volt servo.
This is my first try with a direct power high voltage servo.
At 11.1 volts, it should output 48kg at 0.125 seconds response time. I may experiment with higher voltages once I work out a better power input. The stock servo has a single jst plug, which I am very skeptical of it being able to draw 12+ volts without melting.
I will power the servo with a 2000 mah 3s lipo. The servo has a second cable for the receiver that will connect only to the signal and ground wires.
Dan B from the Arrma forums is advising me.
I will post update after I set things up. If things look exciting I will post a video for demonstration purposes.

Are you sure servo is the issue, lots have issues with steering due to servo nut being loose or weak servo saver spring. A 70kg servo you shouldn’t be having issues even with a budget servo.

 

[Trucking in space]

Are you sure servo is the issue, lots have issues with steering due to servo nut being loose or weak servo saver spring. A 70kg servo you shouldn’t be having issues even with a budget servo.

Servo nut LocTite-ed well. Not checked the saver yet. Not sure what to look for. I'll see if there's a video on YouTube. I've been afraid to mess with the servo saver, as I don't know what is "too tight" and am worried about damaging my servo from too tight a saver setting. I'll see if the manual has a section regarding servo saver adjustment. I didn't think to check the manual until now.

One of my thoughts was that I'm running 2 large 40mm fans, two sets of LEDs, and this likely inefficient servo. I'm thinking maybe at higher speeds, the servo cannot pull enough amps to apply full turning torque. I run a quality lipo rated for 150C, but I wonder if the dumboRC receiver is supplying enough amps to the servo.

I just got the AGF servo installed. This is a test without my endpoints set (they're 70% right and 65% left, where it was for my previous servo) properly yet.

I'm running at 12.6 volts right now, which is the minimum voltage for this servo, 3s 2000 mAh lipo connected to the servo, no external BEC.

I had a busy day at the animal shelter and then had to drop off my nephew's birthday gift. Too dark to run my truck outside.

At 12v it has 48 kilos of torque and is 0.125 seconds in response time.

And I gotta say, this is the first servo I've run that I fully believe the numbers in the spec sheet. I think this cost me $68 approximately after tax. I'm a happy customer.



Check it out:

 

[Horatio]

What model of AGF servo are you running at 12.6v?

 

[Horatio]

Just for reference - even their 1/5th scale servos are:

I think over-powering them will result in magic smoke under load.

4.8 - 8.4v.

Anything higher than that will burn out the FET's in the servo. And fairly soon on that sort of voltage.

Or have I missed the memo on a new range of servos that run on 240v?

 

[Nelson.81]

What model of AGF servo are you running at 12.6v?

Sa75

 

[Nelson.81]

Servo nut LocTite-ed well. Not checked the saver yet. Not sure what to look for. I'll see if there's a video on YouTube. I've been afraid to mess with the servo saver, as I don't know what is "too tight" and am worried about damaging my servo from too tight a saver setting. I'll see if the manual has a section regarding servo saver adjustment. I didn't think to check the manual until now.

One of my thoughts was that I'm running 2 large 40mm fans, two sets of LEDs, and this likely inefficient servo. I'm thinking maybe at higher speeds, the servo cannot pull enough amps to apply full turning torque. I run a quality lipo rated for 150C, but I wonder if the dumboRC receiver is supplying enough amps to the servo.

I just got the AGF servo installed. This is a test without my endpoints set (they're 70% right and 65% left, where it was for my previous servo) properly yet.

I'm running at 12.6 volts right now, which is the minimum voltage for this servo, 3s 2000 mAh lipo connected to the servo, no external BEC.

I had a busy day at the animal shelter and then had to drop off my nephew's birthday gift. Too dark to run my truck outside.

At 12v it has 48 kilos of torque and is 0.125 seconds in response time.

And I gotta say, this is the first servo I've run that I fully believe the numbers in the spec sheet. I think this cost me $68 approximately after tax. I'm a happy customer.



Check it out:

Don’t be afraid of tightening it

Servo nut LocTite-ed well. Not checked the saver yet. Not sure what to look for. I'll see if there's a video on YouTube. I've been afraid to mess with the servo saver, as I don't know what is "too tight" and am worried about damaging my servo from too tight a saver setting. I'll see if the manual has a section regarding servo saver adjustment. I didn't think to check the manual until now.

One of my thoughts was that I'm running 2 large 40mm fans, two sets of LEDs, and this likely inefficient servo. I'm thinking maybe at higher speeds, the servo cannot pull enough amps to apply full turning torque. I run a quality lipo rated for 150C, but I wonder if the dumboRC receiver is supplying enough amps to the servo.

I just got the AGF servo installed. This is a test without my endpoints set (they're 70% right and 65% left, where it was for my previous servo) properly yet.

I'm running at 12.6 volts right now, which is the minimum voltage for this servo, 3s 2000 mAh lipo connected to the servo, no external BEC.

I had a busy day at the animal shelter and then had to drop off my nephew's birthday gift. Too dark to run my truck outside.

At 12v it has 48 kilos of torque and is 0.125 seconds in response time.

And I gotta say, this is the first servo I've run that I fully believe the numbers in the spec sheet. I think this cost me $68 approximately after tax. I'm a happy customer.



Check it out:

you’ll not over tighten it, see how tight mine is on my buggy, and another pic someone else’s where they’ve put a 17mm wheel nut on also nearly completely locks it. If you put your hand on one wheel hold it down and turn the other wheel if your servo is to loose you will see it split under the load hard to describe without a video but it in 2 pieces a v design, you want it to move a bit under a heavy load but not so easily that it effects steering.

 

[Horatio]

So am I right in saying that the AGF 81BHMW has a better spec at 6-8.4v than the SA75 does running at 10-13v?

There are possibly other aspects regarding the differences between the brushless motor in the 81BHMW Vs the Coreless motor in the SA75.

But the Coreless servo is great bang per £€$....

 

[Nelson.81]

So am I right in saying that the AGF 81BHMW has a better spec at 6-8.4v than the SA75 does running at 10-13v?

There are possibly other aspects regarding the differences between the brushless motor in the 81BHMW Vs the Coreless motor in the SA75.

But the Coreless servo is great bang per £€$....

I’m not sure in later videos he adds a correction to the results when making pulls think it was something to do with length or servo horn or tie rod can’t remember is a while ago I went down the servo rabbit hole watched these., but any agfrc servo u not gonna go wrong. Not sure if he maybe tests the A86 in another vid.