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Old 12-19-2018, 10:38 PM
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Default power versus torque at rpm

I hope that a few people understand my intentions with this post. i chose to put it in its own thread so that people can feel free to disagree without the fear of me turning it into a contest. Iíll also do my best to help anecdotal understandings and comparisons but its much easier to share as a community if you are coming from a position that you and anyone in the thread could be wrong and its ok to learn.

Power in high performance electronics (batteries, motors, and ESCs specifically) is not a universal measurement to determine good from bad. power is a rule of thumb for some and a thermal limit quasi-anecdote for others.

most electronics publish a continuous duty rating. Marketing groups convince owners of the company to tell the engineers to rate the product to an industry standard or a common practice or market making ratings. continuous means continuous for some, 10 minutes for some, and 5 minutes for others.

Having allot of power doesnt help you win races unless its useable. The only way to make sure its useable if to break it down into its elements. Torque and rpm. Some torques and rpms are better than others as measured by the amount of heat they generate. Some torques and rpms are more important to the track than other torques and rpms. The motors job is to meet the requirements of the track as efficiently as possible.

​​​​​as a manufacturer you have to make a decision on what your max duty cycle is based on a curve. You pay the bills by selling motors or batteries or esc. you pay the bills for a long time when those electronics last a realistic amount of time. So a manufacturer picks a continuous rating based on previous limitations and needs. They publish a number that should be whatever they agreed continuous rating should be but there is a peak and an intermittent value that may or may not get published and there is certainly not a good explanation of what they are and why you care.

if an electric motor can burst to 120 amps but only runs at a constant speed of 5 amps what do you really understand about the motor. you could say power. If the motor is 5 amps at 30 degrees timing but 10 at 31 can you really say you understand power? in non rc engineering if someone calls and asks for a 1/2 horsepower motor nobody will answer unless the marketing department forces them to. they will ask you how much toque you need at what rpm. The biggest reason is because electric motors have an efficiency curve that goes beyond what the motor can continuously do but if the continuous rating is 10 minutes and you only need 1nm of torque for 30 seconds you can buy a motor much smaller because the smaller motor can cross over continuous for 30 seconds and rest for 9:30. This is a standard. its a standard because of economics. if a robot manufacturer asks 3 motor suppliers for quotes on a 1/2 hp motor who will have the lowest cost and be the most efficient? there is no downside unless you dont understand your own motor.

so there are 3 curves. continuous, peak and intermittent. they could represent arcing across insulators or thermal limits. they also apply to a battery. if you take apart a lipo and put it under a very powerful microscope and compare good to bad you will see granulation on the surface of the internal conductors of the anode or cathode (i cant remember). they know the rate of granulation increases with higher heat and that is all they can conclusively say right now (couple years ago). if you go above the continuous rating of a battery by allot for a short amount of time it will recover if it rests for awhile (maybe just lower consumption) but certainly less than the continuous rating.

torque is different at all rpms because efficiency is different. your loads are different and acceleration requires allot more torque than braking or continuous motion. power doesnt really help you build a lightweight dynamic cost effective product. if it help you to be faster great but you can have less failures, be faster, cheaper, if you understand that a rating isnt really anything if the mfg doesnt tell you what it means and the RC world is the wild west. getting what you want starts with an understanding of heat generation, efficiency, and dissipation. what the acceleration and continuous torque/rpm profile is needed for a track and load. ​​

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Old 12-20-2018, 12:57 AM
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You seem to be confusing power and amps. Motors, wires etc are generally rated by amps. A simple way to get more power output without exceeding the amperage rating is to use a higher voltage.
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Old 12-20-2018, 05:06 AM
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i think his logic comes from 1/10th scale racing being limited to 2S lipo , so the voltage is fixed at 8.4V max.
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Old 12-20-2018, 09:12 AM
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By definition, "Power" is a measure of Watts which is calculated (using Ohm's Law) by multiplying Volts times Amps to get Watts:
https://www.wikihow.com/Calculate-Wattage

By definition, "Horse Power" is calculated by multiplying Torque times RPM:
Power and Torque: Understanding the Relationship Between the Two, by EPI Inc.

For tuning mechanical timing on the end bell for stock racing, most manufacturers will provide a recommended current draw at 8.4V for use with a motor analyzer like this one here:
https://www.rcjuice.com/skyrc-brushl...r-checker.html

For example, I run a Trinity motor in 13.5T stock buggy and they recommend setting the timing to 5.6A draw. The digital timing takes an average across 3 phases measured independently and they almost never match up to what the reading on the end bell says regardless of the brand of motor. Anyway, you want to periodically check/adjust your timing as the end bell can shift in a crash and magnetic strength will fade over time which will require you to adjust the timing to get max optimal power
draw without wasting energy/heat.

If you want to find optimal gearing in addition to optimal timing, then you would want to invest in a dyno similar to this product here:
https://www.minipro.com/products/chassis-dyno
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Old 12-20-2018, 01:35 PM
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Originally Posted by Bry195 View Post


torque is different at all rpms because efficiency is different. your loads are different and acceleration requires allot more torque than braking or continuous motion. power doesnt really help you build a lightweight dynamic cost effective product. if it help you to be faster great but you can have less failures, be faster, cheaper, if you understand that a rating isnt really anything if the mfg doesnt tell you what it means and the RC world is the wild west. getting what you want starts with an understanding of heat generation, efficiency, and dissipation. what the acceleration and continuous torque/rpm profile is needed for a track and load. ​​
So when will your line of motors be available for sale?
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Old 12-20-2018, 08:28 PM
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Originally Posted by UK.hardcore View Post
i think his logic comes from 1/10th scale racing being limited to 2S lipo , so the voltage is fixed at 8.4V max.
Maybe... but 1/10th scale racers don't talk about 1/2 horsepower motors either.
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Old 12-20-2018, 09:19 PM
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Originally Posted by gigaplex View Post
You seem to be confusing power and amps. Motors, wires etc are generally rated by amps. A simple way to get more power output without exceeding the amperage rating is to use a higher voltage.
Im not confused. If you dont understand you are welcome to ask. power is electrical and mechanical.
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Old 12-20-2018, 09:29 PM
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Originally Posted by billdelong View Post
By definition, "Power" is a measure of Watts which is calculated (using Ohm's Law) by multiplying Volts times Amps to get Watts:
https://www.wikihow.com/Calculate-Wattage

By definition, "Horse Power" is calculated by multiplying Torque times RPM:
Power and Torque: Understanding the Relationship Between the Two, by EPI Inc.

For tuning mechanical timing on the end bell for stock racing, most manufacturers will provide a recommended current draw at 8.4V for use with a motor analyzer like this one here:
https://www.rcjuice.com/skyrc-brushl...r-checker.html

For example, I run a Trinity motor in 13.5T stock buggy and they recommend setting the timing to 5.6A draw. The digital timing takes an average across 3 phases measured independently and they almost never match up to what the reading on the end bell says regardless of the brand of motor. Anyway, you want to periodically check/adjust your timing as the end bell can shift in a crash and magnetic strength will fade over time which will require you to adjust the timing to get max optimal power
draw without wasting energy/heat.

If you want to find optimal gearing in addition to optimal timing, then you would want to invest in a dyno similar to this product here:
https://www.minipro.com/products/chassis-dyno
I mentioned some torques and rpms are better than others and matching the motor capabilities to the track.
If a motor has an efficiency bell curve from say 30 to 90 back down to 30 and efficiency is e-power in versus m-power out what is 5.6 amps? Efficiency is plotted on a torque rpm curve. Its a series of points that create a bell. If we understand that current is torque, not 1 torque but lots of torques on this efficiency curve a deep understanding of amps doesnt help.

once you understand torque/rpm and the corresponding efficiencies for each torque rpm you might get a feel for what to do next. The next thing to do is understand the torque/rpm requirement of the track (each time slice) and align the the curve of the motor to the curve of the track requirements.

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Old 12-20-2018, 09:55 PM
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Originally Posted by 071crazy View Post
So when will your line of motors be available for sale?
Motors are my job and rc is my passion. The minute RC becomes work Iíll spend more time doing my real job...it pays better and its still a pretty good gig. Im who a machine builder comes to when he wants to sort packages at 17000 per hour or synchronize 1000 servos to control the curvature of a satelite dish or accelerate a roller coaster. I even consult on making sure you dont have to flush twice for municipalities.

20 years ago i was the guy doing design work drudgery and now I help those guys solve a problem that nobody else could help them with. im not going to sell a motor. That is my job. How many car mechanics get excited about selling their products or services in their free time?

Im here to help because i enjoy it, its easy, I get to trade what I know for what i dont know. The same thing helped me get where i am in my career and has made me happy to return....the way i believe is right.

honestly, i make this offer because it makes me feel good and I get something but I have strong reservations about how much information I provide to those who dont give a person the benefit of the doubt first. There is a massive language gap and at times i hear allot of stuff that sounds like people are satisfied not understanding more.

The good news is that there are just as many people that are close and want to evaluate something new or in depth that they dont get a chance to evaluate.
I will attempt to help the over zealous beginner and the guy in the middle with way too much cynicism and the senior guy who understands logic but has a system. Just keep in mind what im trying to provide can become work but it has passion behind it. We all make mistakes and even do good things that have unintended results for ourselves and others. Give me and the others around you a chance and Iíll do the same.


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Old 12-20-2018, 10:22 PM
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Originally Posted by Bry195 View Post

you are on to something. If a motor has an efficiency bell curve from say 30 to 90 back down to 30 and efficiency is e-power in versus m-power out what is 5.6 amps? Efficiency is plotted on a torque rpm curve. Its a series of points that create a bell. If we understand that current is torque, not 1 torque but lots of torques on this efficiency curve a deep understanding of amps doesnt help.
I believe that 5.6A is the point at which both lines intersect when measuring max efficiency crossed with max power... I trust that Trinity has already spent a great deal of testing their equipment before coming up with the 5.6A setting for their motors. I also believe different brands of motors will yield different optimal timing settings, and gearing too! I recently switched from a Trinity Monster Max to Trinity Punisher (both set to 5.6A) but I had to bump up from a 27T pinion to 31T pinion with the Punisher. I don't have a dyno, but I can feel the Punisher has way faster acceleration which tells me it offers far more torque and power, but I have no method to measure this other than looking at my lap times and taking temp readings... perhaps someday I might have enough disposable cash to invest in a dyno which would provide accurate measurements of each component we are discussing.
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Old 12-20-2018, 10:43 PM
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I spoke of an efficiency curve like a bell that sits in an x-y plot of speed and rpm. Lets say timing is dynamic and always perfect. Your bell would be wide. Lets say timing is not dynamic but its perfect for some arbitrary narrow band of rpms that we will call x. If you add a load you know the torque. Now you can say x=1 and y=2 and see where it sits inside the bell. We dont have 1 efficiency for the motor its a range of efficiency with several bands that are varying degrees of ok, good, better, best and bad. The drive train is designed around the application and the work it does (power requirement) has a mass.

Mass requires torque to move it. Acceleration means you need allot more torque. Torque equals current and acceleration means you need allot more torque for a short amount of time. If a 1hp motor can convert 1amp of current into 1nm all day long how do i help you understand that 100 amps in a motor 30mm in diameter has no relevance in a conversation about power? The numbers i used are common in figures in motors with specifications. i probably pushed a little more current through my 30mm motor but its not that big of a leap. When I explain this inequality my hope is that you see 100 amps is only relevant for acceleration for a very short period of time. Lets say that a 30mm motor is a 1/20hp motor. Do you need 100 amps to do work with a 1/20 motor? No. You needs it to accelerate it. If the motor goes through a band of efficiency that is bad, better, good, best where is all the current going that is the difference between 100% and the band? Its turned into heat. So what is optimal? When you accelerate you want to minimize heat generation and make sure you bypass bad and better and accelerate through good and best most of the time. Less heat and more mechanical conversion happens. If i know i have 5.6 amps (torque) at 18000 rpm do i know how efficient I am? Maybe but i doubt it. you know the motor wonít overheat under some situations but 5.6 amps is allot of current for a 1/20 motor and its certainly not 5.6nm. Its an average power that is not continuous and not peak so what is it? Its a rule of thumb for the motors ability to dissipate heat for an average amount of load, accelerations, and efficiencies. If its on the average 60% efficient all the time while going through the bell curve the motor can dissipate the other 40% as heat without cooking. 5.6 amps times 40 percent is the amount of heat the motor can dissipate into air based on its thermal efficiency. Its a good number to understand to keep things from breaking but you are building a system that wont burn and you should be building a system that accelerates to an rpm first and then narrowing the choices by the motors thermal efficiency. Even if you only have 1 motor. Because the point is to average the efficiency, torque and rpm requirement for a 1450 gram mass accelerating 20 times to 25mph in 12 seconds. Then you use the torque/rpm and efficiency curve to put your track and timing dead center in the middle of the curve. 100 amps at 40% is way different than 100 amps at 80%. You know you can change the mass or the FDR and timing to move the curve to that average requirement and low efficient accelerations are a thing of the past.
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Old 12-21-2018, 12:27 AM
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Originally Posted by Bry195 View Post

Im not confused. If you dont understand you are welcome to ask. power is electrical and mechanical.
I'm quite aware of the distinction. However you kept refering to amps as unit of power. It is not.
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Old 12-21-2018, 07:28 AM
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Originally Posted by gigaplex View Post
I'm quite aware of the distinction. However you kept refering to amps as unit of power. It is not.
based on the level of my topic do you honestly think I dont understand power, amps, and torque?

Sometimes I move in and out of terms like I have a fluent audience but its ok to ask for clarification if you want to understand.

current and torque is almost an equality for the sake of our topic
efficiency-e-power in versus m-power out
acceleration-a change in speed per second per second
inertia-a resistance to change in speed
thermal time constant-heat dissipated per second
torque constant-unit of torque per amp
commutation (timing)-the relationship between the rotor and the sensors that changes over load, temperature and rpm.
peak (current)-for less than a second usually limited by the insulation of the stator
intermittant-usually a temperature limit for 10 seconds usually wrapped around the melting point of the insulation
continuous-the torque or power that a motor can do all day long
torque curve-x-y plot that visualizes efficiency, torque at an rpm, duty cycle, continuous, peak, power and rpm.

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Old 12-22-2018, 03:16 PM
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Originally Posted by Bry195 View Post

based on the level of my topic do you honestly think I dont understand power, amps, and torque?

Sometimes I move in and out of terms like I have a fluent audience but its ok to ask for clarification if you want to understand.
I can only comment against what you wrote. With posts as long as yours, it would be an easier read if we didn't have to second guess what you wrote vs what you meant by misusing some terms.
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Old 12-22-2018, 08:55 PM
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Originally Posted by gigaplex View Post
I can only comment against what you wrote. With posts as long as yours, it would be an easier read if we didn't have to second guess what you wrote vs what you meant by misusing some terms.
You dont need to second guess. You are allowed to ask questions. Iíd love to help you understand. Maybe read it in small chunks or with a friend. Make sure you are well rested but fully awake. If you were sentenced to read my posts by nature of some weird cyber crime and court Iíd much rather talk about that.

Motion control has 3 levels of control
1-Torque (current)
2-velocity (a little toque plus velocity gets you power)
3-position

Everything is a product of 1.

Really the way RC motors are rated is quite brilliant from a warranty and customer satisfaction perspective.
If you design a high performance motor and you want to communicate with your customers in a way that minimizes damage, complexity, and tools creating a suggested amp rating is pretty smart.

​​​​1-Tools to measure amps are easier to find than tools for most other control parameters (efficiency, power, ...)
2-The number can be selected to open the product up to more people in wider ranges of applications and still minimize self destruction ​.
3-5.6 amps is not what the motor would draw when its working at a constant load. Its not what​ it would draw during acceleration.
4-you could say its an arbitrary number to set timing but if you put more timing in the motor goes even faster so why wouldnt you just set the timing to a speed or set the timing really high to get more speed?
5-the only thing that i can mathematically connect 5.6 amps to is heat. Continuous heat to be specific

Im adding an eddy current brake to my minipro so when I get it back from the machine shop Iíll load the flywheel to a constant recommended current value and see if the motor temperature stabilizes or continues to climb.

Last edited by Bry195; 12-22-2018 at 09:11 PM.
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