Motor Analyzer

[Nvr_Fst_Enuf]

Fairly new to RC and currently running dirt ovals...i have a motor analyzer that I have been playing with and comparing different motors of the same type...ie just stock 13.5, 17.5

But, i really dont know what the results should be. The three 13.5t had different rpm's from 25k to 20k, 2.6a to 1a.....

So, when I tune my ext timed motors, what am I looking for? Low RPM with low Amps??

 

[Tunedfrog]

Welcome in @Nvr_Fst_Enuf

 

[Greywolf74]

Fairly new to RC and currently running dirt ovals...i have a motor analyzer that I have been playing with and comparing different motors of the same type...ie just stock 13.5, 17.5

But, i really dont know what the results should be. The three 13.5t had different rpm's from 25k to 20k, 2.6a to 1a.....

So, when I tune my ext timed motors, what am I looking for? Low RPM with low Amps??

Welcome to RCT!

I'm no expert on racing but from what I understand you want the highest KV with the lowest amp draw. In other words you want to run the fastest motor that uses the least amount of amp draw. The motor analyzer allows you to compare these aspects, and others, of different motors to see which ones perform better and to let you see the exact gains your getting when adjusting the motors timing.

For example if you have two 13.5T motors and Motor A is (grabbing numbers out of thin air) hitting 3500kv and pulling 1.5A and motor B is hitting 3300kv and pulling 2A then motor A is clearly the better motor. Not only is it a faster motor (higher kv) but its also pulling less Amperage. Amp draw is important in racing because the lower your amp draw the longer you can maintain higher voltage on your lipo. The higher your voltage is the faster you're motor will run because higher RPMs will be maintained for longer allowing you to churn out faster lap times.

Where it can sometimes be confusing is When motor A is 3200kv and 1.5A and motor B is 3500kv and 2A. Motor A has the advantage in the amp draw category but motor B has the advantage in the KV category. So which one is better? The best way I know of to answer that question would be to take them out and run practice races with each of the motors. Each practice race should be done using fully charged identical battery packs or the same battery pack. You want to keep the results as consistent as possible between the test races. Ideally youd want to run a datalogger and capture the average battery voltage from your best races. Once you have the battery's averaged maintained voltage of each practice race then you can use those numbers along with the KV numbers from the motor analyzer to get an RPM rating. Whichever motor shows the highest average RPMs would be the better motor to use.

For example. Lets say Motor A (3200kv/1.5A) maintains an average voltage of 7.3V on a 2S pack during the course of the test race and Motor B (3500kv/2A) maintains an average voltage of 7.0V on a 2S pack. Again pulling numbers out of thin air. So now that we have our average volatges we can plug those numbers in to see which motor had the higher average RPMs for the test races.

Motor A: 7.3V x 3200kv = 23,360 Average RPM for the test race.
Motor B: 7V x 3500kv = 24,500 Average RPM for the race.

Motor B would be the faster motor and would be the one youd want to use in a real race. Of course this doesn't take in to account tuning the motor and playing with things like motor timing etc to get the highest performance possible out of the motors first.

If you didnt have access to a datalogger you could also compare the motors by running the same types of test races using the 2 motors only just make note of your race completion times and go with the motor with the faster times.

Hope this helps.

 

[Nvr_Fst_Enuf]

Okay, that makes sense. I omittted that the analyzer shows the rpm. But I was told by a local racer that the lower RPM motor with low amps would be the better motor. I was thinking the opposite...

Attached are 5 different Juststock 13.5t motors I was playing with...

 

[Greywolf74]

Well I'm no racer so i could be off base but I do know a fair amount about electronics, motors, and batteries and If I was racing I would want to turn as fast of lap times as I could and the best way to do that (at least in my mind) is to be able to maintain the highest rpms possible throughout the course of the race. That being said if your KV/RPMs are to high for the track (for example a small tight track) you might not be able to utilize the full KV of the motor and you'll burn more amps going on throttle coming out of corners which in turn will lower battery voltage faster. Lower the battery voltage the less RPMs you'll be able to make later in the race.

The RPMs on the analyzer wont tell you the same information as the average RPMs for the course of a race like I was talking about above. What I was talking about above has more to do with maintaining the highest possible RPMS throughout the whole race where as the only thing the RPM meter on the analyzer shows you in max possible RPMs given the batteries current voltage. What I was talking about above is whats important.

Have all of those motors been tuned for optimal timing? I would think youd have to do that before the comparisons would be meaningful.

 

[Nvr_Fst_Enuf]

Well I'm no racer so i could be off base but I do know a fair amount about electronics, motors, and batteries and If I was racing I would want to turn as fast of lap times as I could and the best way to do that (at least in my mind) is to be able to maintain the highest rpms possible throughout the course of the race. That being said if your KV/RPMs are to high for the track (for example a small tight track) you might not be able to utilize the full KV of the motor and you'll burn more amps going on throttle coming out of corners which in turn will lower battery voltage faster. Lower the battery voltage the less RPMs you'll be able to make later in the race.

The RPMs on the analyzer wont tell you the same information as the average RPMs for the course of a race like I was talking about above. What I was talking about above has more to do with maintaining the highest possible RPMS throughout the whole race where as the only thing the RPM meter on the analyzer shows you in max possible RPMs given the batteries current voltage. What I was talking about above is whats important.

Have all of those motors been tuned for optimal timing? I would think youd have to do that before the comparisons would be meaningful.

The track is an oval, a tight, banked oval. A 65 lap main means your on and off the throttle a minimum of 130 times and thats really only feasible if you had a clear track all 65 laps....i underatand the difference in average rpm vs. the max the motor is capable of.

These 5 motors inparticular are fixed timing from hobbywing. I do have others for different classes that have external timing. So, I am trying to determine what is the optimal equation (high KV + low RPM + low amp), so I can optimaly tune my other motors....

 

[Greywolf74]

Your equation is contradictory. KV and RPM proportional to each other. The higher the KV the higher your RPMs are going to be at a given voltage. If it were me the main 2 things Id be looking at is highest kv for the lowest amp draw. I wouldnt worry about trying to look at average RPMs unless you end up in a scenario like I painted above where you have two motors who are close in KV but the higher KV has a higher amp draw. The only way to figure out which of those motors is going to be faster is to either time them or datalog average voltage to figure out which motor had higher average RPMs through a race. If you're never really stretching the motors legs though, if its just constantly back and forth between say 15% throttle to say maybe a max of 60% throttle then Id probably just look for the lowest amp draw as the kvs wont matter nearly as much. In the pics above Id probably go with the 2498kv/1A motor. An extra 1/10 of an Amp draw isnt worth an extra 20kv in my mind and if you can't get the cars up to 3/4 throttle or faster then the extra 600kv wont be helpful and the extra 1.6A draw would be detrimental I believe. I'm starting to see why that guy at your track said go with the lowest amp draw lowest kv although Id go with the higher kv if the amp draws were the same or maybe if I could get a lot more kv for very little amp draw difference. Not 100% sure about that last part. Id have to do some testing to be sure.