14LikesTrying to understand FDR vs. Motor timing
05-09-2017, 08:26 AM
#1
Trying to understand FDR vs. Motor timing
If increasing spur or decreasing pinion equals an increased FDR which equals increased torque/decreased speed which leads to decreased motor temps that allows you to increase timing.
If the above is true and the ideal FDR for my car on a given track is 4.0. I put the appropriate gears in it to get an FDR of 4.0. I then run the car several laps with the motor timing at zero and gradually increase timing till I reach the appropriate operating temp. When finished motor is only at 15 degrees.
Question: Would it be beneficial to increase the FDR so I could increase the motor timing? is there a general rule or is this done on a motor/car specific bases? and lets assume everything else remains the same. Thanks
If the above is true and the ideal FDR for my car on a given track is 4.0. I put the appropriate gears in it to get an FDR of 4.0. I then run the car several laps with the motor timing at zero and gradually increase timing till I reach the appropriate operating temp. When finished motor is only at 15 degrees.
Question: Would it be beneficial to increase the FDR so I could increase the motor timing? is there a general rule or is this done on a motor/car specific bases? and lets assume everything else remains the same. Thanks
05-09-2017, 08:32 AM
#2
If increasing spur or decreasing pinion equals an increased FDR which equals increased torque/decreased speed which leads to decreased motor temps that allows you to increase timing.
If the above is true and the ideal FDR for my car on a given track is 4.0. I put the appropriate gears in it to get an FDR of 4.0. I then run the car several laps with the motor timing at zero and gradually increase timing till I reach the appropriate operating temp. When finished motor is only at 15 degrees.
Question: Would it be beneficial to increase the FDR so I could increase the motor timing? is there a general rule or is this done on a motor/car specific bases? and lets assume everything else remains the same. Thanks
If the above is true and the ideal FDR for my car on a given track is 4.0. I put the appropriate gears in it to get an FDR of 4.0. I then run the car several laps with the motor timing at zero and gradually increase timing till I reach the appropriate operating temp. When finished motor is only at 15 degrees.
Question: Would it be beneficial to increase the FDR so I could increase the motor timing? is there a general rule or is this done on a motor/car specific bases? and lets assume everything else remains the same. Thanks
05-09-2017, 08:36 AM
#3
get the motor tuned for the application and gear it to the track. way much simpler.
a team scream motor i had in my 12th i had tuned and geared it to the track, way easier. you dont have to worry about timing anymore. gear it to how it feels on the track and temp
a team scream motor i had in my 12th i had tuned and geared it to the track, way easier. you dont have to worry about timing anymore. gear it to how it feels on the track and temp
Last edited by phatboislim; 05-09-2017 at 10:39 AM.
05-09-2017, 12:42 PM
#4
If you have some time, there's some really good tips and info in this series of articles. Brushless motors have some quirky torque and hp characteristics, so adjusting timing and FDR can be counter-intuitive sometimes.
Hope this helps.
https://pphaneuf.github.io/rccars/ar...timing-blinky/
Hope this helps.
https://pphaneuf.github.io/rccars/ar...timing-blinky/
05-09-2017, 12:54 PM
#5
Correct, but gear it for the infield more than the straight....
05-09-2017, 03:51 PM
#8
Allowing timing adjustment has helped level the playing field in classes where different motors are being run. In slower classes like VTA, even the older Novak 25.5 motors can still be competitive when people can adjust the timing on each individual motor and find where the motor performs the best. The individual racers can find the gearing that suits the individual track and be relatively close.
The only way a fixed timing motor class would work is if it was ONE manufacturer only AND the manufacturer was willing to stake their reputation that each and every motor was the same. Of course this is never going to happen as motor manufacturers are happy to sell motors that vary because they know there are suckers out there that will buy multiple motors just to find the "best" one.
If someone wants to race a locked timing motor, several motor manufacturers make motors with locked end bells. All someone has to do is create a class (or mandate locally) that used those motors. But then people would complain that there are too many classes.
05-09-2017, 04:02 PM
#9
Just like the days of 27 turn locked timing motors where people changed brushes, changed springs, cut comms every run, used comm drops, polished bushing, and all other types of ways to fine tune the motor. It was never a level playing field with motors during the 27turn locked timing days.
Allowing timing adjustment has helped level the playing field in classes where different motors are being run. In slower classes like VTA, even the older Novak 25.5 motors can still be competitive when people can adjust the timing on each individual motor and find where the motor performs the best. The individual racers can find the gearing that suits the individual track and be relatively close.
The only way a fixed timing motor class would work is if it was ONE manufacturer only AND the manufacturer was willing to stake their reputation that each and every motor was the same. Of course this is never going to happen as motor manufacturers are happy to sell motors that vary because they know there are suckers out there that will buy multiple motors just to find the "best" one.
If someone wants to race a locked timing motor, several motor manufacturers make motors with locked end bells. All someone has to do is create a class (or mandate locally) that used those motors. But then people would complain that there are too many classes.
Allowing timing adjustment has helped level the playing field in classes where different motors are being run. In slower classes like VTA, even the older Novak 25.5 motors can still be competitive when people can adjust the timing on each individual motor and find where the motor performs the best. The individual racers can find the gearing that suits the individual track and be relatively close.
The only way a fixed timing motor class would work is if it was ONE manufacturer only AND the manufacturer was willing to stake their reputation that each and every motor was the same. Of course this is never going to happen as motor manufacturers are happy to sell motors that vary because they know there are suckers out there that will buy multiple motors just to find the "best" one.
If someone wants to race a locked timing motor, several motor manufacturers make motors with locked end bells. All someone has to do is create a class (or mandate locally) that used those motors. But then people would complain that there are too many classes.
21.5 Turn Monster Locked
if racers want to go fast then just run mod
05-09-2017, 09:40 PM
#13
There are more and more places where people have accepted a level playing field means controlled motors (locked timing and sealed motors) with the compromises attached to that choice. And it doesn't matter what motor is chosen, as long as everybody agrees they would only use that.
A pioneer of this solution was the Australian club where it was decided to run for Mini class the sensorless Hobbywing motor+ESC combo a while ago. They proved that level playing field racing was not only possible but also very successful. ETS followed soon after, now in Australia there are other clubs that have adopted this strategy with their own choice of motor for local racing and they all showed success. Reports from Europe show the same thing. It is a matter of political will at club level, that's all.
Our friend who opened the thread sounds like he might have a hard time ahead of him. Unfortunately, no level of understanding can help if you have a motor that just doesn't measure up against the motor of the week.
Back to torque versus power, the website linked above has some good explanation. I think if there was a little math in it, it would make the point more clear. Power is actually torque times RPM times 2pi. This is how the two are related. In the real world there are other things to consider, but this law is the fundamental constraint. Real factors only detract from this maximum achievable (keep RPM a given and measure the others and you'll find power a little bit less due to friction, heat, conductor imperfections, magnetic conductivity variation and so on). Also keep in mind some of the power is wasted in turning the rotor itself. As the explanation shows in the linked website, at some timing, this power becomes significant (i.e. the motor is wasting more power to turn its rotor than there is available to spin the wheels = heat).
Unfortunately, we don't have any means of measuring on board what happens with the motor, our only option is an indirect measure by monitoring temperatures. There are other means but they're also indirect (like measuring the current draw with an onboard logging device). This tells you something again, but it is still an indirect measure (you don't know if the higher current draw is because you're accelerating or because the motor is simply out of its power band).
As demonstrated above, the temperature you're measuring is the cumulated effect of the effort the motor has to expend to spin its own rotor AND the wheels of your car. Hence the problem with this strategy. You don't know what is causing the temperature you read to be what it is. Is it the too advanced timing, or is it the effort of accelerating the car and maintaining the top speed (assuming you get there)? The short answer is that you don't know and the only way to (sort of) find out is to test until you get a lot of data. Time consuming and not always practical. You may not have the track to yourself long enough to collect enough data in one sitting, next day the weather may be different, track and air temperatures changed, your data is no longer directly comparable/consistent with yesterday's data.
To build a correct graph of power and torque versus RPM for any given motor involves more than just a motor analyser (I don't have one, but looking at the construction, I would say it's all done in software by using some assumptions you do not control). You would need a proper motor dyno, just like the real car dynos, and you would need to know what is in the software to be able to construct the graph. Once you have the graph, you're on easy street. Set timing and gearing to keep the motor at peak torque (= choose timing curve that has the highest torque and pinion/spur combo that keeps motor RPM always at or near this point all the way around your track) and bob's your uncle.
This is of course based on another assumption, i.e. that your track is technical with more corners than straights. If your track is open, you want max power, of course. Not that easy, eh?
All of that does however serve to make the point that if you want level field racing you need everybody to have a motor dyno and select their motor, timing and gearing for the track every time a new motor comes on the market, or you can just specify the motor, lock the timing (the best gearing will become obvious after quick test) and go have fun.
From what I have seen people are not yet prepared to accept this simply because some have invested piles of money in the motor of the week. All the other stuff you hear about, too slow, too many classes, etc, it's just excuses.
A pioneer of this solution was the Australian club where it was decided to run for Mini class the sensorless Hobbywing motor+ESC combo a while ago. They proved that level playing field racing was not only possible but also very successful. ETS followed soon after, now in Australia there are other clubs that have adopted this strategy with their own choice of motor for local racing and they all showed success. Reports from Europe show the same thing. It is a matter of political will at club level, that's all.
Our friend who opened the thread sounds like he might have a hard time ahead of him. Unfortunately, no level of understanding can help if you have a motor that just doesn't measure up against the motor of the week.
Back to torque versus power, the website linked above has some good explanation. I think if there was a little math in it, it would make the point more clear. Power is actually torque times RPM times 2pi. This is how the two are related. In the real world there are other things to consider, but this law is the fundamental constraint. Real factors only detract from this maximum achievable (keep RPM a given and measure the others and you'll find power a little bit less due to friction, heat, conductor imperfections, magnetic conductivity variation and so on). Also keep in mind some of the power is wasted in turning the rotor itself. As the explanation shows in the linked website, at some timing, this power becomes significant (i.e. the motor is wasting more power to turn its rotor than there is available to spin the wheels = heat).
Unfortunately, we don't have any means of measuring on board what happens with the motor, our only option is an indirect measure by monitoring temperatures. There are other means but they're also indirect (like measuring the current draw with an onboard logging device). This tells you something again, but it is still an indirect measure (you don't know if the higher current draw is because you're accelerating or because the motor is simply out of its power band).
As demonstrated above, the temperature you're measuring is the cumulated effect of the effort the motor has to expend to spin its own rotor AND the wheels of your car. Hence the problem with this strategy. You don't know what is causing the temperature you read to be what it is. Is it the too advanced timing, or is it the effort of accelerating the car and maintaining the top speed (assuming you get there)? The short answer is that you don't know and the only way to (sort of) find out is to test until you get a lot of data. Time consuming and not always practical. You may not have the track to yourself long enough to collect enough data in one sitting, next day the weather may be different, track and air temperatures changed, your data is no longer directly comparable/consistent with yesterday's data.
To build a correct graph of power and torque versus RPM for any given motor involves more than just a motor analyser (I don't have one, but looking at the construction, I would say it's all done in software by using some assumptions you do not control). You would need a proper motor dyno, just like the real car dynos, and you would need to know what is in the software to be able to construct the graph. Once you have the graph, you're on easy street. Set timing and gearing to keep the motor at peak torque (= choose timing curve that has the highest torque and pinion/spur combo that keeps motor RPM always at or near this point all the way around your track) and bob's your uncle.
This is of course based on another assumption, i.e. that your track is technical with more corners than straights. If your track is open, you want max power, of course. Not that easy, eh?
All of that does however serve to make the point that if you want level field racing you need everybody to have a motor dyno and select their motor, timing and gearing for the track every time a new motor comes on the market, or you can just specify the motor, lock the timing (the best gearing will become obvious after quick test) and go have fun.
From what I have seen people are not yet prepared to accept this simply because some have invested piles of money in the motor of the week. All the other stuff you hear about, too slow, too many classes, etc, it's just excuses.
Last edited by niznai; 05-09-2017 at 10:07 PM.
