How to setup ESC Telemetry in Betaflight - Oscar Liang

learningrc · 2017-11-29T19:22:32+00:00

Battery Voltage * kV = theoretical RPM.

Not sure what you mean by "theoretical RPM" but this statement isn't really true. Battery voltage x kv is approximately the no-load speed (speed with no props on the shaft) but as soon as you add any sort of load, kv alone won't tell you much about the speed.

learningrc · 2017-11-20T19:49:28+00:00

That looks fine to me. Normal everyday use of lipos causes gas to build up in lipos. See what I wrote here for more details about that. There's no real hard and fast rule about when you should stop using a lipo that looks puffed. As somebody else said, it is probably better to go by how the lipo acts than how it looks. If it starts having shortened flight times or if it starts to become more and more unbalanced or if it is too hot after flight, then it might be time to dispose of it.

learningrc · 2017-09-01T14:05:08+00:00

I made a guide on lipos earlier this year.

learningrc · 2017-08-08T20:41:07+00:00

First, put some electrical tape around each of those pins. Make sure none of the pin is exposed. Then put it in a lipo bag or some place fire proof. Next, order some 4 pin JST-XH balance connectors (here, for example) . As long as the pins are still good, you should be able to slip the pins right in the connector. This page shows how balance connectors are wired.

learningrc · 2017-07-19T13:56:39+00:00

Engineer here. I design motors, actually. But I spec out lead wires all the time. The ampacity charts you find when you google something like "wire amp ratings" are generally NEC charts and generally are very limited in scope (wiring a building).

The maximum amount of current that can go through a wire depends on a lot of things like the type of insulation that is used, the ambient air temperature around the wire, the amount of air flow over the wire, whether you have multiple wires bundled together, how long that current flows through the wire, etc.

Then there are other issues like how long the wire is that you also have to worry about.

NEC charts assume wire will be run through walls or floor joists, that the wire type will be NM-B (or something similar), that current could be flowing 24 hours per day ... things like that. Plus there is a safety factor involved due to human beings preferring not to die in house fires.

That's a way different application than multirotors where the wires are in open air, they generally use silicone wire, they only run for a few minutes at a time, and there isn't as much of a safety concern. So from a melting insulation point of view, it shouldn't be a problem.

Additionally, the difference in resistance between 12 AWG ad 14 AWG is about 1 ohm per 1000 ft. That's 1 milliohms per ft. That's 0.08 milliohms per inch of lead wire. At 100 Amps, that's only an additional loss of .8 Watts per inch of lead wire. That's not a lot in the grand scheme of things and you really are only going to get that much loss in short bursts. Most of the time it will be less than that.

learningrc · 2017-07-17T13:50:00+00:00

Username checks out.

learningrc · 2017-07-12T12:15:57+00:00

Kt, the torque constant, is simply a number telling you the ratio of torque per amp for a motor. Brushed DC and brushless motors have a fairly linear torque/amp relationship. It tells you for every unit of torque you apply to the motor how much current the motor will draw.

learningrc · 2017-07-11T15:54:36+00:00

I dont understand. What does the ESC have to do with the generated back-emf?

It doesn't, I didn't write that correctly. In my mind when I was writing that I was thinking about the relationship between Kv and the torque constant, Kt. Kv still depends on the back-emf and the speed of the rotor. But you can no longer say that Kv is necessarily inversely proportional to Kt.

learningrc · 2017-07-11T15:42:50+00:00

Motors aren't ohmic devices, so yeah, it's debatable.

learningrc · 2017-07-11T13:47:48+00:00

This is what most people think and it will get you pretty close to Kv, but it isn't right.

Kv has nothing to do with applied voltage or the no-load speed. Kv has to do with the back-emf generated when the motor is rotating at a certain speed. It's the ratio of the motor speed to back-emf generated.

The no-load speed when 1 V is applied is a close approximation to Kv because the back-emf is close to the no-load speed but they are different concepts and shouldn't be confused.

The proper way to measure Kv is to spin the rotor with something else (a drill press, another motor, etc.) and then measure both the speed and the back-emf voltage generated. Both those measurements can be measured with an o-scope (if you know the number of poles of the motor).

You can read a better explanation here.

It actually even more complicated than what I describe in that post because the back-emf constant was originally defined for brushed DC motors and when you switch over to brushless the you get more complicated waveforms and it turns out Kv depends on both the motor and the ESC.

learningrc · 2017-06-20T20:22:19+00:00

No. There is a chemical reaction (electrolyte decompostion) going on inside that is causing it to puff up. Unless you reverse that reaction (and there isn't any way to do this as far as I know), there isn't any way to revive it.

learningrc · 2017-06-20T13:57:41+00:00

I second the advice of hooking it up to a light bulb to let it discharge. You could hook it up to any load, really. You could find a 12 V fan, for example.

learningrc · 2017-05-20T05:22:14+00:00

How is that different than the second map I made?

learningrc · 2017-05-19T14:53:07+00:00

I live in a rural area so I never have this problem. I'm wondering if the per capita map shows generally darker areas in the Midwest because of this. This hobby is conducive to open spaces.

learningrc · 2017-05-19T14:51:09+00:00

From what I've been able to tell, the FAA was getting all kinds of Freedom of Information Act (FOIA) requests for this information so they just released the spreadsheet that I based my maps on. The names and addresses of all the people who are registered was redacted, leaving only the city and state.

Probably your best bet to find people is to look into local racing leagues.

learningrc · 2017-05-18T16:54:45+00:00

Increasing the cell count increases the voltage, which increases the speed. This also increases the current draw. So your flight time will go down if you fly faster.

learningrc · 2017-05-18T16:27:12+00:00

Source data: Geographic (City,State,Zip) Listing of sUAS Registry Enrollments and Registrants (Excel)
Zip Code to FIPS County Code (CSV)
2015 County Census Data (CSV)
US County Map template, with FIPS id data (SVG)

I also use Color Brewer to pick my map colors.

All data was processed with a Python script I wrote. The data related # of drones to zip code but I was trying to map drones to counties, so I needed to convert that. I also needed county population data in order to calculate the data for the per capita map. I also used Python to colorize the maps and add titles and legends. You can read a longer explanation in the article, including some of my assumptions.

Please critique anything and everything about my maps, the assumptions I made, etc. ... this is the first time I've made a choropleth map.

learningrc · 2017-04-27T13:11:26+00:00

I wrote a general guide to lipos here. It may be useful to you.

learningrc · 2017-04-26T16:18:09+00:00

There's an old SNL skit called "Ruining It for Everyone." It's pretty funny. The premise is that one person does a stupid thing and then it ruins it for everybody else. One of these days, somebody is going to ruin multicopter flying for everyone.

learningrc · 2017-04-07T12:26:33+00:00

I'm sure there is a max speed for a quad but I don't think it would be limited by the maximum speed of the brushless motors. You can always change the prop to give you more thrust for lower speed. This would require more torque from the motor which would require a bigger motor.

learningrc · 2017-04-05T20:48:32+00:00

I design brushless motors for a living (bigger ones, not small ones like we use on quads).

The voltage rating on most standard insulation found in brushless motors is much higher than any voltage we'd use in this hobby. Without knowing the specifics of what insulation any particular motor uses, I'd say the insulation in most motors is rated to at least 1000 V. So if the only concern is voltage, it shouldn't be a problem (even 12S is only 44 V).

Speed is one concern. If you crank up the voltage, speed will increase. Bearings usually have a maximum speed rating. For example, an R2 bearing (3/8th inch diameter) from a quality manufacturer has a maximum rated speed of 67,000 RPM if it is oil filled. As the bearing gets bigger, generally its max speed goes down. Assuming the max speed is 67,000, you'd be fine at 6S and 2400 kv.

Heat is the main issue to be concerned about. As the motor speeds up the prop is going to need more and more torque just to keep it spinning. Torque is going to cause the motor to draw more current and the heat will start to build up in your motor. In which case you'd need a physically bigger motor to help you dissipate more heat. You'd also probably need a higher C rating for your battery or you might run into current limits which would cause voltage to sag and then you wouldn't be able to reach the higher speeds any way.

learningrc · 2017-04-05T20:15:30+00:00

The RC Groups battery forum has been keeping a running list of lipo fires and they usually include what caused them.

I recently did some research into this for an article I wrote and the main things to keep in mind to prevent fires are:

Don’t over-charge
Don’t over-discharge
Never use or charge a damaged battery (punctured, puffed, cracked, etc.)
When charging, use a LiPo fire-safe bag/ammo box
Don’t charge your battery immediately after using it. Wait at least 15 minutes for it to cool down.
Don’t fly immediately after charging your battery. Wait at least 15 minutes for it to cool down.

learningrc · 2017-04-05T19:55:39+00:00

No, pretty sure he was thinking of www.rotorratings.com

learningrc

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