18 replies to this topic

[Dave_12]

How is a brushless motor rev checked ?

[Wink Hackman]

Very easily . I made a disc from acetal that push fits onto the shaft. It's black with a piece of reflective white tape stuck on. Connect motor to power supply via ecom, point tachometer (few quid on ebay) at spinning disk and read the number! A 4000kv motor at 10 volts should be doing 40000rpm - usually it will be one or two thousand below the target figure, but pretty close.

[dalek]

I checked the no-load RPM of three KC 4500 Kv motors at 10 volts using a Remora ESC. I also tried an X89 ESC and the results were the same.

One of the motors spun at almost 49,000 RPM, another spun at about 48,000 and the third one at about 46,000.

When I tried each of them in the same car, the fastest motor gave me the fastest lap times and the slowest motor gave me the slowest lap times.

To take the RPM readings using an optical tach, I made a disc (to represent a two-bladed propeller) out of masking tape cut in a circle about the same diameter as the motor and put a hole in the middle of it so it slid over the motor shaft and stuck to the side of the motor. I then used a black magic marker to darken two areas of the tape across from each other.

I was able to reuse the disc on all three motors.

When I took the RPM readings, I turned off the room lights (because they blink at 60 hz) and used a headlamp (head mounted battery powered light) for illumination to make sure I got accurate readings.

Besides accurate readings, I like using a headlamp because it frees up both hands as well as letting me put light right where I need it.

[MSwiss]

Interesting.

 

The 3,000 RPM difference, top to bottom, made what difference in lap times?

[dalek]

Interesting.
 
The 3,000 RPM difference, top to bottom, made what difference in lap times?

In a lane at P1 raceway where the fastest motor might run a 3.2 second lap time the slowest motor would run about a 10th slower than that.

[MSwiss]

Thanks Dale.

 

I was going to guess a .1.

 

It's interesting to hear concrete evidence that they vary fairly significantly. 

 

I remember at the onset of brushless, some people here on Slotblog were convinced that removing brushes from the componentry of the motor would result in them all running the same.

 

IOW, you'll only need to buy one to run in the front of the pack.

[Dave Crevie]

Having been in manufacturing for, well, forever, I can assure you that not every motor that comes off an assembly line is going to be perfect. Even those assembled by robots. There will be peccadilloes on that line that will cause some motors to not be assembled perfectly. Doesn't matter if it is brushed, brushless, or turbo-jet. A certain percentage will have variances in how carefully they were put together. Add to that fact, that some cheaper manufacturers are going to cut corners to reduce costs, which also effects quality. Having built a lot of motors over the years, I have to admit that, when I built several motors to take to a race, that were supposed to be identical, they were all a little different in performance. I think any top open wing car racer will back me on that.

 

The only way around this is to have someone at the point of sale, test every motor, using very stringent criteria. And be willing to discard a lot of motors.  

[Hot Slots]

I thought brushless motors all pulled the same RPM? The future of slot cars, equal powered motors. Fair consistent racing.

That's the same variances the CR-102's pull.

And I don't have to worry about ESC issues with my CR-102's.


Interesting post Dale.

[bbr]

sure there r variations in rpm bc being cheap chinese products,  spec r not going to b tight

 

but what I value is the performace will not degrade over time, nothing to wear out but the bb, which are replaceable

 

no magic bullet here, but imo a better choice for me, but ymmv. choose ur poison and enjoy

[Ken Lenz]

Well well, again we have misguided information about brushless.  We go from WD-40 motor baths to dark room magic with miner’s helmets to support an expert with no experience claim.  Just the food Swiss is looking for to chew on negatively about brushless!  Dale, you cannot use masking tape and a black marker to get proper readings from optical tachometer, OMG read the instructions!  With lack of data to review and support the here-say I’ll bet the motors Dale tested were not brand new out of the box either.

Today, so you have firm information and data to review I invested the time to test three brand new out of the box 4500Kv BLDCs.  Mike there NOT a 3,000 rpm difference in brushless motors!  In fact the BLDCs have less than 1% variance in rpm from one to another and the X89 ESC is faster than the WestRock.  The full test results are attached for review.
 

…end

Attached Files

•  4500 BLDC Test Report.pdf   301.29KB   14 downloads

[Samiam]

You guys will never achieve the perfection of the brushed motor and its flawless history in racing. Not a single issue ever with any of the dozens of classes of brushed motors. Throughout the history of slot car racing the brushed motor has proven itself as a flawless power plant with not a single controversy ever. Good luck trying to match that kind of perfection. 

 

 

Thread locked in 3......2.....1...... 

[MSwiss]

sure there r variations in rpm bc being cheap chinese products,  spec r not going to b tight

 

but what I value is the performace will not degrade over time, nothing to wear out but the bb, which are replaceable

 

no magic bullet here, but imo a better choice for me, but ymmv. choose ur poison and enjoy

Mike,

I'm pretty sure you've never raced one competively, week after week, where you can make that statement with 100% certainty. 

 

I read the chit chat on FB , especially the heated rhetoric while the ISRA Worlds was going on.

 

There were complaints of cars needing pushstarts(in both the brushed and brushless classes) brushless cars more prone to bending chassis, because of the freewheeling nature of them when they deslot, and one I was surprised to hear, rumors of top racers changing their brushless motors between races, after moving up, because the neo magnets were losing their oomph, due to heat. Again, IIRC, it was portrayed as a rumor.

If you look hard enough on FB, at ISRA time, I guarantee you'll find the comment.

[Dave Crevie]

Today, so you have firm information and data to review I invested the time to test three brand new out of the box 4500Kv BLDCs.  Mike there NOT a 3,000 rpm difference in brushless motors!  In fact the BLDCs have less than 1% variance in rpm from one to another and the X89 ESC is faster than the WestRock.  The full test results are attached for review.
 

 

 

1% of 40,000 is 400. That could be significant in a racing event. 

 

Before I will believe test results on anything, it will have to come from an outside source like UL or Consumers Reports, not a manufacturer. Allowing the food distributors to do their own testing is why we have recurring cases of food poisoning. 

[Ken Lenz]

Before I will believe test results on anything, it will have to come from an outside source like UL or Consumers Reports, not a manufacturer. Allowing the food distributors to do their own testing is why we have recurring cases of food poisoning. 

Coming from the heavy duty truck manufacturing industry as VP of Engineering I will tell you that that industry is self-tested.  Very little testing is done third party.  Since you are such a skeptic think of that next time you ride alongside an 18 wheeler.  Also, UL does not have a category for testing these motors.  Believe what you will.  In closing find a tin can that can produce 1% variance and I bet you are racing them.

[Dave Crevie]

Coming from the aerospace industry, I know more than you think I do. That aside, I don't race brushless, and have no plans to do so. So I am not going to argue this subject, as you believe I am. Slot racing is a hobby. Every participant can enjoy it however they want. But they should have accurate and unbiased info from which they can make that decision.

[Ken Lenz]

… I don't race brushless, and have no plans to do so.

… Slot racing is a hobby.

….But they should have accurate and unbiased info from which they can make that decision.

You don’t race brushless and yet pipe in your 2 cents.  Slot Racing is a hobby and KC Racing is a businesses that supports the hobby.  When you affect my business with your slander in a public forum it becomes personal.  You continue with slander in a claim the tests are inaccurate and unbiased.  I would stop now.

[Dave Crevie]

There has been no slander here. At no time did I say that you were selling a bad product. You attacked a person's possibly unscientific method of testing. Were you there when he performed those tests? In industry, when there is a possible question of the efficacy of test results, a third party arbitrator is brought in. But that is not necessary here. We are just trying to enjoy a hobby. From me, people are encouraged to buy your product if that is the way they want to go. 

[bbr]

thanks MS for ur insight,,, yay racers will destroy a items as long as it makes it thru a race 

 

KL nice test report

 

for me,,, I have not bought a brushed motor 4 1/24 in two years lol,,, but about over 100 bl motors n 25+ esc 

[vanges]

At the other end of the continent, Argentina, we are having these same discussions as well.