Kraton Steering servo - How much torque do we really need?

[Thumper33]

How much torque does a Kraton or Talion really need? I'm sure it depends on the tires, but I think a good discussion on this would be healthy.

Also, out of curiosity while on the subject, is there a such thing as too much torque? I mean, if we put 1000 oz-in in there, do we start breaking steering linkages when the tires get unknowingly stuck or something and we try to turn?

 

[Monster Dork]

Too much torque, and your rig will push the earth out of its way instead of turning the car.

I think every 6s Arrma needs exactly 444 oz-in of steering torque.

 

[Clubin]

Speed is another factor. Too fast makes it hard to control too. I like a fast servo!

 

[Mazin]

From a standing position if you move your steering back and forth really fast it should dig to china.

 

[Adiabatic]

Exactly 666oz-in and Satan will reach up through the ground and help your wheels turn.

 

[Monster Dork]

Yeah, but Reef's doesn't sell a 666 oz-in servo (yet).

 

[SrC]

Can you ever have enough torque???
I think a 35 kg servo is a minimum. And fine for all for all the stock 6s rigs.
If you anticipate very heavy large and belted tires, you could always use more torque.
I find the higher the torque, the slower the servos are for the most part.

 

[Infraction666]

I like the Savox 2290 in my Kraton, set at 7.4v and it's hav 50.0kg/694.4oz torque, i add a ekstra shims to the servo saver .

It's nice with those badlands mx38 belted

 

[dazed1]

I like the Savox 2290 in my Kraton, set at 7.4v and it's hav 50.0kg/694.4oz torque, i add a ekstra shims to the servo saver .

It's nice with those badlands mx38 belted

View attachment 207878

Does it rotate them with ease?

 

[Infraction666]

Does it rotate them with ease?

It's works fine for me

Also runs those Katar belted

 

[Kingpin]

Who needs a servo when you have the power of Telekinesis.

 

[morrjr71]

I use a Powerhobby 729MBL servo in my Kraton 6s. It is a brushless, waterproof servo that has 500 oz-in of torque and a speed of .100 seconds at 7.4 volts. Like many things in the world of RC, in the past month they went up in price from $89.95 to $94.99.

https://www.powerhobby.com/powerhobby-729mbl.html

I have two of these servos in crawlers and one in my Kraton.

 

[Thumper33]

I appreciate the input guys, but I don't want to focus on which servo model or brand is best, but more so what specs we should be looking for. Teach a man to fish ya know...

I realize that there are variables like how big of a tire are you trying to turn, and how heavy those tires are. I appreciate the comment about speed. I didn't realize that there was such a thing as too fast of a servo. Seems like the answer there would be "well just slow down your fingers". LOL But it makes sense. Maybe making an analogy to real cars, show me the race car that can turn the wheels lock to lock in .1 seconds anyway, let alone faster than that.

Is there some kind of accepted objective test to see if a servo is strong enough? I'm just throwing this out there as an example guess of a test... take the tires off and turn full lock to lock and note approximate time. Put the tires on and the car on the ground and repeat. If the lock to lock time slows down then your servo isn't strong enough. Again, guessing. I suppose one could also account for gyroscopic force and spin the tires up to speed and do a 3rd test. Though I might also suggest that the faster the car is going, the slower you want it to turn so you don't make huge corrections at high speed.

One thing that would also be constructive is a comment such as "I tried servo xxx with xxx tires and it wasn't strong enough. I could tell it wasn't strong enough because..." That would help us dial in min torque req's.

Thoughts?

 

[morrjr71]

What you propose is not an objective test, but a subjective test. You would have to do hundreds of tests to come to any kind of conclusion, if you even could.

There are objective tests for servo torque and speed, which is how servos are rated. They are performed on a calibrated machine so there are no variables (tires, vehicle weight, etc.) that enter the picture. Check out RC Review on YouTube: you will find test of servos in various price ranges and recommendations.

What one person thinks is strong enough might be different than what another person thinks is strong enough for the same vehicle. I think you will find that a lot of people go for higher torque servos than are actually needed for a given situation. Crawlers generally need a more powerful servo because they may not be moving when the steering is engaged, whereas a basher is almost always moving and requires a servo with less torque and speed.

 

[MambaSenton]

I think we all can attest to the stock s652 being underpowered for a K6 out the box..

when looking for stronger I took the 265oz it allegedly puts out and decided I needed to double that for my liking of turning and mobility.

Therefore to answer the main question I feel you need 400min to 500 to adequately turn those copperheads. I’d probably go for a another 505 or 630 being I like pro-modeler n they only make certain Oz’s.

Also must keep in mind majority of the max output whether 400-700 is usually ran at full tilt 8.4 bec?

 

[morrjr71]

MambaSenton makes a good point: when looking at servo specs look at the specs for the BEC voltage you will be running at.

 

[SrC]

I appreciate the input guys, but I don't want to focus on which servo model or brand is best, but more so what specs we should be looking for. Teach a man to fish ya know...

I realize that there are variables like how big of a tire are you trying to turn, and how heavy those tires are. I appreciate the comment about speed. I didn't realize that there was such a thing as too fast of a servo. Seems like the answer there would be "well just slow down your fingers". LOL But it makes sense. Maybe making an analogy to real cars, show me the race car that can turn the wheels lock to lock in .1 seconds anyway, let alone faster than that.

Is there some kind of accepted objective test to see if a servo is strong enough? I'm just throwing this out there as an example guess of a test... take the tires off and turn full lock to lock and note approximate time. Put the tires on and the car on the ground and repeat. If the lock to lock time slows down then your servo isn't strong enough. Again, guessing. I suppose one could also account for gyroscopic force and spin the tires up to speed and do a 3rd test. Though I might also suggest that the faster the car is going, the slower you want it to turn so you don't make huge corrections at high speed.

One thing that would also be constructive is a comment such as "I tried servo xxx with xxx tires and it wasn't strong enough. I could tell it wasn't strong enough because..." That would help us dial in min torque req's.

Thoughts?

Understand that with hobby grade servos, The speed and torque specs listed by the Mfr are usually overrated by as much as 30%.
If you consider what Arrma installs as stock, the torque is very minimal. To save coin, I am sure. They are just $5.00 cheap servos in reality. Doesn't even pay to warranty them at all. Until you install a real proper servo, you won't appreciate the performance and drivability of your rig.
I found that 35 kg servos are just about right as a minimum requirement. If you slam your rig with alot of alloy, it becomes much heavier, so more torque in a servo is paramount. And if your Servo saver is too weak and not shimmed properly or not using the optional "X-Hard" SS spring, your servo and steering will not perform at its best. Many overlook this part and feel the servo is the issue. NOT.
And I also don't like servos that are too fast when it comes to bashing. Any decent radio worth its salt can dial down servo speed and Expo. to your liking IF needed. That is subjective to us all.
More servo speed, the better, out the box. And I just dial in my servo where I like it sometimes. With Larger MT wheels and off road, this is less important. With my Lim and Infr. and On Road rigs, this is more important.
Super fast servos are most beneficial at the track for confined technical driving. And that takes a different skillset when driving like this. And even the track guys will dial in their servos using Steering Exponential and speed trims at the radio.

 

[dazed1]

One thing that need to be mentioned is that the usual recommend servo on this forums are the Amazon ones, and they are like 40% less powerful them what they are rated for, so when one is stating the minimum requirements he should say real 25kg of torque instead of I guess Inflated 35. I have big doubts that real 25kg is not enough for 95% of 6s line up, knowing the performance of stock brands servos are like 1/2 of the the claimed numbers. So even with 25kg you are 2-3x above the current stock offerings

 

[Thumper33]

Dazed has a point. Makes me want to make a test rig and buy a bunch of servos to test. Makes ya wonder though. Anyone live near pro modeler or some other "top end" manufacturer? I'm sure they have test rigs for qc, and maybe would be willing to put some other manufacturers' gear on their rig for a "whip it out" contest. LOL

 

[21STalion]

450oz is plenty, your already easily moving the EXB servo saver spring out of the way at that point. More might be nice but your probably not getting much more steering without doing other things.