Hobbywing Tunalyzer VS SkyRC Motor Analyzer - The Stock Racing Rant Part 1

[@mike._.feliciano6782]

Question, that Yowoo battery you have is a 2S so, your volt reading at 16:32 was showing 8.4V. When you put the lead into your Hitec Lipo Checker at 17:36 one cell was showing 4.16v and the other at 4.17v, combined is 8.33v, still not 8.4V but closer to it. I say this because I don't think it's a true inaccuracy. Great video though and I'm learning a great deal.

[@EMU1]

You bring up many good topics in this video. Spec racing is basically pushing the powertrain and car setup to the absolute limits. Which is why it typically has a much higher ceiling but lower floor than mod racing as far as tuning is concerned. What I mean by that, spec racing is easier to enter than mod, so it has a low floor. But, to race at the front, the knowledge of EVERY area of the car is VERY important. Maximizing power deliver, efficiency, reducing rotating mass, and coming in as close to the weight limit as possible is pretty much par for the course to race in the A main at big events. The variance between different SkyRC analyzers is noticible. Enough that a "pro" stock driver would want to tune multiple motors with about 50kv difference between them. Test one at an event to see what the offset is between their analyzer and the one at the event, so they can use the fastest motor that will pass. You can notice in your test, that motor temperature matters in testing. Testing cold, the analyzer showed 3602. By the end of the test, it was showing 3620. If you let it run longer, it will test even higher. When we first implemented motor checks with a KV limit, top 3 were tested after the race, and many failed because the motors were hot and showing higher KV's than they would when cold. Generally, as the bearing warms up, it offers lower resistance. (also pro drivers are often replacing the bearings with ceramic in the cans). Test voltage can also change the result, which is why I always like to test with a power supply to control the voltage more accurately. The HW running at a static 7.4v does increase repeatability as it doesnt rely on higher source voltage for "accurate" results. As with any ESC, there is always slight variance in the speed that the motor runs. Similarly, these motor testers have that same variance since they are basically ESC's that read the KV. Your sample size is small, and to have a definitive trend, one would need to test many units to see if the 60kv delta between testers is par for the course. When tuning, you tune to your analyzer, but have to expect that other testers may read higher or lower than the one you have, and prepare for that difference.

[@karlobobiles2968]

Good tip on checking with the local club you’d race at. If they use a particular motor tester, use the same so you’re at least on the same page.

[@mattgrieve774]

I'd be more leery of the constant changing Kv on the Hobbywing more than the 8.5v register on the SkyRC model. I have a SkyRC discharger and the voltage registers differently on that as well but it performs the operation that it's made to do so there's that. I'm pretty sure Kv is something that doesn't change the longer you hold the motor on the Tunalyzer. You're also not using the sensor wire which is going to make a huge difference when it comes to accuracy. EDIT: You may want to try another battery because I've watched 3 or 4 more videos using the SkyRC Analyzer and it's reporting the correct voltage of the battery. None of them are showing 8.5v

[@fuzzfreak1967]

I always thought the point of re-shimming the motor was to get the rotor into its magnetic center for optimal performance….. 🤷‍♂️

[@BASHERSUNITED]

@fuzzfreak1967 that's one thing you can do as well. Sometimes you can even over-shim and have to dial it back.

[@TheRCBuildersPost]

I love both of these units. Like you, I have no idea which is more accurate but I do love my hobbywing tunalyzer more simply for the ESC programming. I don't think I'd spend the money I have on 1/28 motors though but to each their own 😂

[@iansadkovich197]

Can the Hobbywing test at 8.4V?

[@BASHERSUNITED]

Not that I know of. Really the test voltage isn't an issue as long and it's static and consistent. 7.4 volts is the minimum voltage of a 2S lipo so the testing is less affected by a lipo batteries charge status. What would be better is the skyrc being lower.

[@ganeshgavara893]

Hobbywing is around 300$, what does it do more than skyrc?

[@EMU1]

One of the biggest differences is the sensor wire for the HW. Unfortunately we dont have a compatible wire at this time.

[@BASHERSUNITED]

I assume it's just more accurate. A compatible sensor wire may even things up a bit but SkyRC isn't a super accurate based company. They make budget stuff mostly.

[@ganeshgavara893]

Since Kyosho motor uses 10th scale sensor wire, should that work for PN compatible motor or Kyosho motors

[@blessrc1]

The sky RC only works with 2S, not 1S. Hence the incorrect voltage reading when using a 1s battery. I made the same mistake before realizing this.

[@BASHERSUNITED]

I'm running a 2s battery, what i was saying was you can't pull 8.4v out of a 3/4 full 2s battery. The hobbywing one shows the actual voltage of the input battery.

[@Glocktologist]

I think the test voltage could cause this difference. The KV rating of a motor is a nominal number. How many RPMs you actually get per one volt will vary depending on the motor load. Even an unloaded motor is not 100% free of load. It has to overcome friction and air resists the movement of the rotor. At a higher RPM the resistance from these factors is higher so the KV figure will be lower. I bet if you could get the HW to put out 8.4 Volts it would read a lower KV value. Or, turning the SkyRC down to 7.4 Volts would result in a higher KV reading. Based on this test, I’m not even sure these analyzers are off compared to each other. It might very well be that they are both accurate and the difference we observe is caused by the difference in the input voltage.

[@BASHERSUNITED]

Possibly. kv shouldn't change based on voltage. If it did the meter is the issue not the motor. What I was showing is the the skyrc input voltage was incorrect. You can't pull a constant 8.5v from a 8.2v source.

[@Glocktologist]

Do you think anything can cause the KV to change?

[@BASHERSUNITED]

@Glocktologist I think that meters can be incorrect. The kv should vary from motor and heat conditions can affect thus but it's exact range should be measurable by a good meter.

[@Glocktologist]

@BASHERSUNITED I have difficulty wrapping my head around this. As far as I know, Kv is not exactly the value we are told. It is the back EMF at a given rpm: if you run a 3300 Kv motor at 3300 rpm, the B-EMF will be 1 Volt. At 6600 RPM, it’s 2 Volts. This gives the impression that providing 1 Volt makes the motor turn at 3300 rpm and 2 Volts makes it turn at 6600 rpm, as the value is presented to us. However, it’s only true if there is zero load of any kind resisting the rotor movement. In real life, motors may be manufactured to overcome some of the resistance so it meets the value at some rpm, but I don’t know if it’s physically possible to build a motor that increases rpm on a linear slope in relation to the input voltage on an actual test bench. Because differing input voltage can throw off the measurements, I think the accuracy of the motor analyzers can be reliably compared only if you have a constant input voltage for both.

[@BASHERSUNITED]

@@Glocktologist a couple of guys have run this same test with a controlled voltage power supply and had the same results.

[@Jace1283xmod]

The skyrc are not consistent, they differ by as much as 50-60kv

[@pcparas1121]

Why you telling my speed secrets 😝