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Dynamic Torque VS Static Torque on Servos

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Dynamic Torque VS Static Torque on Servos

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Old 01-29-2018, 02:41 PM
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Questions?? Dynamic Torque VS Static Torque on Servos

So I was browsing the new Tekin line-up of servos and found this particular servo to be quite interesting: https://www.teamtekin.com/t250.html

According to the description, it is designed for 1/8 buggies and truggies and would make an excellent addition to your 1/8th scale project, or is it....?

There seems to be two different torque ratings on this servo, Dynamic Torque and Standard (or Static) Torque.

The Static Torque is 245 oz-in @ 6V while the Dynamic Torque is 325 oz-in @ 6V. Of course this model is also compatible with 7.4 and 8.4 Volts as well.

According to the almighty Google, Dynamic Torque is torque found during an acceleration or deceleration, while Static Torque is torque applied to an object that doesn't move (I.E. pressure against a wall, for example)

What is intriguing about this is determining which of these torque ratings applies to the hobby of RC, as this would determine weather or not this servo would be recommendable for use on larger 1/8th scale models (truggies or monster trucks). This is because larger 1/8th scale vehicles have always recommended 300 oz-in of torque or more.

One could argue that the hobby applies dynamic torque, as the servo turns the wheels of a vehicle and therefore puts the wheels under acceleration. However one could also argue that the hobby applies static torque as when the servo reaches its target angle, it then stops, becoming static torque holding it in place. I believe the answer is both, what do you think?

More importantly, which value is more important and pertains more to the hobby? This servo has the potential to be a real heavy hitter on the marketplace, as it is capable of 415 oz-in of Dynamic Torque at just 0.08 sec on 7.4V, the most common BEC setting for 1/8th scale models. This, combined with the fact it is a Tekin product and will undoubtedly have very high resolution and precision ability could make it a very serious contender in the Servo marketplace, competing with the very best such as ProTek, Savox, and MKS. However, if the Static Torque is the more applicable stat, then that puts the Tekin Servos at a massive disadvantage. 282 oz-in of torque on 7.4V is simply UNACCEPTABLE for a servo that according to pre-ordering vendors will cost $160.

Now there are other Tekin servos that will be available with higher torque ratings, but this particular servo is the only one with BOTH the torque and the speed required for a track racer. Will it be able to efficiently take an AE RC8TE around the track with a good lap time?

Another important question comes to mind: Just what specification have other servo manufacturers been giving us this entire time? Well if the Tekin servo is anything to go by, then it would seem that most likely they have been listing Dynamic Torque on their product specifications. What is their static torque? Well Tekin's Static Torque value at 6V of 245 oz-in is about 75% of its 325 oz-in Dynamic Torque value. Its 7.4V Static Value is about 68% of its Dynamic Torque value, and its 8.4V Static Torque Value is about 69% of its Dynamic Torque value, respectively. Therefore, it is safe to presume that about 70% of your servo's shown rating is its Static Torque value. For example this would mean that the Servo I currently want for my next truggy - the ProTek 170SBL, would have a Dynamic Torque of 535 oz-in and a Static Torque of about 375 oz-in at 7.4V.

So what do you guys think of Dynamic Torque and Static Torque? What do you think of the new Tekin Servos? Do you plan on trying them? Do you think these servos will be good for 1/8th scale truggy racers and monster truck bashers, or will it fall short and only be good for 1/8th scale buggies?

Last edited by wallacengineeri; 01-29-2018 at 03:03 PM.
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Old 01-30-2018, 06:18 AM
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I agree, something needs to be done to establish a common method for all brands to use, trusting these torque ratings is no different than trusting the C ratings on batteries, most manufacturers will inflate their numbers because there is no governing authority to keep them in check.

For me, I'll simply strap on some weight and benchmark servos myself for when I'm considering to switch to a new brand just to see if the servo meets my basic expectation:
https://www.youtube.com/watch?v=Ncg8qhtPSVs
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Old 01-30-2018, 11:43 AM
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Originally Posted by billdelong View Post
I agree, something needs to be done to establish a common method for all brands to use, trusting these torque ratings is no different than trusting the C ratings on batteries, most manufacturers will inflate their numbers because there is no governing authority to keep them in check.

For me, I'll simply strap on some weight and benchmark servos myself for when I'm considering to switch to a new brand just to see if the servo meets my basic expectation:
https://www.youtube.com/watch?v=Ncg8qhtPSVs
I really enjoyed the video, great testing methodology man! Its simple and yet very effective. Might take some refining like finding a way to keep the weight from moving around to get absolute accuracy but other than that its a great idea! Those JX servos are really that good? I was about ready to spend $160 on the ProTek RC 170SBL for my racing truggy, but I found a JX servo capable of 450oz-in at 0.07 sec on 7.4V for $75!
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Old 01-30-2018, 12:36 PM
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Thanks

I've got a little over a year experience with the JX servos and I'm completely sold on their solid aluminum case brushless variants... it did take about 10 months of racing to strip a gear in my 1/8 truggy, I simply bought a cheap $8 servo and swapped the gear out with that servo which has been holding up fine for the past 4 months. In my 1/8 buggy, I'm starting to see some slop in the gears after 14+ months of racing, so I've got a couple more donor servos on order to swap out the sloppy gears on that servo next.... can't complain for the performance, I even logged 98.7% consistency with the sloppy JX servo too!
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Old 01-30-2018, 12:45 PM
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Originally Posted by billdelong View Post
Thanks

I've got a little over a year experience with the JX servos and I'm completely sold on their solid aluminum case brushless variants... it did take about 10 months of racing to strip a gear in my 1/8 truggy, I simply bought a cheap $8 servo and swapped the gear out with that servo which has been holding up fine for the past 4 months. In my 1/8 buggy, I'm starting to see some slop in the gears after 14+ months of racing, so I've got a couple more donor servos on order to swap out the sloppy gears on that servo next.... can't complain for the performance, I even logged 98.7% consistency with the sloppy JX servo too!
That isn't bad, but seeing how you are replacing gears on servos, the PorTek might actually be worth the money. I don't know, I will have to think about it. The fact is though that a high quality servo such as the ProTek or Savox or MKS will go years without a single thing ever failing. That is the good thing about going "premium" and spending the extra money.

Not gonna suggest for even one second that these JX servos are bad though, that is really good for nearly a year of racing. Very good value for the price, I would say. Its just that if you are truly serious and want consistent performance for years, then maybe you should try the ProTek or an MKS as some point.
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Old 01-30-2018, 01:12 PM
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I have heard of an occasional gear strip on the ProTek servos too, in fact pretty much all brands of servos will strip a gear eventually, big difference between brands is customer service and gear sets, etc... there are no gear sets for JX, but the cost for a sacrificial $8 servo is still less than $25 for most name brand gear sets

Another selling point is that there are more US based dealers for ProTek than JX, the only US dealer I know for JX is RCJuice, but I don't think RCJuice handles any warranty issues and that's where most folks don't want to take any chances on an occasional dud. I have heard of one guy who burned up a JX within minutes, and he swore he set their EPA properly, etc...

As far as sloppy gears go, I've heard all brands will get sloppy as they age too, there is no such thing as a gear set that lasts forever. I will admit that 1 year is a bit premature for slop on the JX though... I used to get 2-3 years on my Savox servos before those gear sets needed to be replaced in my 1/8 cars. Though some quick math shows me that JX is still more cost effective even if I have to replace a stripped/sloppy gear once a year... the break even point could be indefinite depending on how often a name brand servo goes through respective gear sets too.
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Old 01-30-2018, 02:08 PM
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Originally Posted by billdelong View Post
I have heard of an occasional gear strip on the ProTek servos too, in fact pretty much all brands of servos will strip a gear eventually, big difference between brands is customer service and gear sets, etc... there are no gear sets for JX, but the cost for a sacrificial $8 servo is still less than $25 for most name brand gear sets

Another selling point is that there are more US based dealers for ProTek than JX, the only US dealer I know for JX is RCJuice, but I don't think RCJuice handles any warranty issues and that's where most folks don't want to take any chances on an occasional dud. I have heard of one guy who burned up a JX within minutes, and he swore he set their EPA properly, etc...

As far as sloppy gears go, I've heard all brands will get sloppy as they age too, there is no such thing as a gear set that lasts forever. I will admit that 1 year is a bit premature for slop on the JX though... I used to get 2-3 years on my Savox servos before those gear sets needed to be replaced in my 1/8 cars. Though some quick math shows me that JX is still more cost effective even if I have to replace a stripped/sloppy gear once a year... the break even point could be indefinite depending on how often a name brand servo goes through respective gear sets too.
Well Ive seen 4-5 years out of name brand servos, even in racing conditions weekly. So based on that personal experience I have to say that the name-brand servos are better. I never really experienced slop from my Savox, either.
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Old 01-30-2018, 03:19 PM
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Interesting. Prior to this the only manufacturer who I had noticed to give static and dynamic servo torque separately was Highest. Never really looked at Tekin servos.

What's more is that Highest's servos have much higher static than dynamic torque, while Tekin seems the opposite. The DT750 servo I have in my SCTE 3.0 has 20.7kg/cm static and 13.8kg/cm dynamic torque on 6V. That is a big difference and it's hard to say which one I'm supposed to compare to other brands! I suppose in this instance it's not such a big deal since it is good enough for that regardless, which is the most important thing of course. But it'd still be nice to know.
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Old 01-30-2018, 03:42 PM
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Originally Posted by tvih View Post
Interesting. Prior to this the only manufacturer who I had noticed to give static and dynamic servo torque separately was Highest. Never really looked at Tekin servos.

What's more is that Highest's servos have much higher static than dynamic torque, while Tekin seems the opposite. The DT750 servo I have in my SCTE 3.0 has 20.7kg/cm static and 13.8kg/cm dynamic torque on 6V. That is a big difference and it's hard to say which one I'm supposed to compare to other brands! I suppose in this instance it's not such a big deal since it is good enough for that regardless, which is the most important thing of course. But it'd still be nice to know.
Huh, higher static torque? That is pretty weird to be honest.
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Old 01-31-2018, 07:32 AM
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Originally Posted by wallacengineeri View Post
Huh, higher static torque? That is pretty weird to be honest.
Mmm not really, at least if you think of it from a "biological" point of view. You could think of it like... well, let's say bench pressing. You maybe be able to get a heavy weight off the rack and hold it there (static), without being able to actually perform a lift (dynamic) with that same weight.
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Old 01-31-2018, 10:10 AM
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Originally Posted by tvih View Post
Mmm not really, at least if you think of it from a "biological" point of view. You could think of it like... well, let's say bench pressing. You maybe be able to get a heavy weight off the rack and hold it there (static), without being able to actually perform a lift (dynamic) with that same weight.
Ah that makes sense
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Old 01-31-2018, 10:53 AM
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What I would like to know about these servos, is the resolution.

Tekin claims to be using Digital Magnetic Position Encoder and from what I could find was a fancy way of saying hall effect sensor. They dont however offer what resolution this offers, and how they have mitigated the more fragile nature vs a potentiometer.

And god forbid you ask these questions on the Tekin thread. You called a troll when you compare a 150+ servo to something common like a savox.
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Old 01-31-2018, 11:08 AM
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My understanding is that digital servos are dependent on the resolution of the radio system, there comes a point where resolution is no longer humanly detectable and becomes nothing more than a marketing gimmick. I'm thinking 8 bit resolution will be perfectly fine for most folks.
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Old 01-31-2018, 12:23 PM
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Originally Posted by billdelong View Post
My understanding is that digital servos are dependent on the resolution of the radio system, there comes a point where resolution is no longer humanly detectable and becomes nothing more than a marketing gimmick. I'm thinking 8 bit resolution will be perfectly fine for most folks.
Let me clarify what I mean by resoultion.

Lets use the savox TG1258 because savox actually publish the resolution.

A 1258 has 12 bit resolution, this equates to 4096 steps of change when put through analog to digital conversion(ADC). We also know this happens over a maximum travel of 130. This gives you 31.5 steps per degree of movement.

Good primer on 12 bit and ADC

I think my assumptions are correct, but I'm open to being wrong. I would also agree this maybe over kill for most.

My questions and problems come around when Tekin makes the claim they have a superior solution with their DMPE, I just want to see if DMPE has better resolution over a given arc. It would also be nice if savox stated the servo's deviation when doing a full sweep. Tekin list this, but I cant find any other servo's to compare this to.
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Old 01-31-2018, 12:33 PM
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Radiopost offered 32 bit resolution:
Radiopost RP3009M - (Torque Type Servo)

I ran one of their servos for a while and I couldn't tell any difference, my lap times didn't change whether I ran a $120 servo or a $20 servo. There is a point of diminishing return on improved resolution and I believe 8 bit is where it's at, however, I believe you're limited to the lowest resolution between the radio and servo... for example: having a 32 bit servo will be limited to 16 bit if that's all the radio can handle.
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