DJI Mavic Pro vs Platinum Flight Times What Caused the Increase?


I have followed the technology advances like farm drones observing water drainage to crop decay, construction degradation monitoring, and potentially drones placing building frames instead of people. But the other day, something caught my eye with DJI Mavic Pro and its sibling DJI Mavic Pro Platinum.  What was interesting, is that the flight time between the two drones, (27 minutes increased to 30 minutes) and how they drive their motors. See the below diagrams.

Sine Drive vs Trap Drive

According to the the above picture they say the propellers and the motor ESC drivers improve noise control and stability. It is true that if the motor commutation is done with Sine drive (right diagram) vs trap-drive/6 step drive (left diagram), the system will have improved stability. An improved shape and material can also improve noise reduction also. But what also happens is that the motor will perform more efficiently giving the motor more thrust for the same amount of current commanded.

What is the different between trap-drive and sine-drive?

Quick info:
In a brushless motor that is in most drones, there are 3 phase lines. Each will be controlled independently but in combinations.

Trap-Drive:
-Commands the next phase combination to turn the motor when the motor state changes, usually by reading hall effect devices or x-y sensor data.
Pros:
-Easy to implement in code quickly and effectively
-Does not need extra hardware to read voltage on the phase lines of the motor.
-Does not necessarily need hall effect devices or xy sensors to move the brushless motor.
Cons:
-Does not command the motor at the right time. This won’t allow optimal torque out of the motor.
-Less efficient = More heat and Less flight time.
-Less consistent with torque output.

Sine-Drive:
-Continually commands the phase lines of the motor to allow the current and Voltage to follow the back EMF curves (see right diagram from above) of the motor to provide optimal torque at all times.
Pros:
-Makes the use of a motor very efficient by allowing the same amount of current to be used and achieve the best torque  the motor can provide.
-Better efficiency = less heat on board and more flight time possibly less weight.
-Near perfect consistency with torque output.
-Less current ripple on circuit board means less noise getting on radio lines which means farther flights.
Cons:
-Harder to implement in code.
-Need more components because more information is needed to be able to commutate in sine-drive.
-Motors can be sensitive if not coded correctly.

It is cool to see commercial companies start putting in software and hardware architecture to improve flight times, reduce weight, and increase flight distances.

Even though the Mavic Air just came out which has some pretty cool features, I am probably going to get the Mavic Pro Platinum with the FPV Goggles because of the farther flights and longer flight time. Hope I can get a hold of one and get flying again soon.

Credit: All pictures are from DJI.com website and not of my own making.
Disclaimer: This blog is solely Tinee9’s opinions through electrical engineering experience and does not have exact knowledge of the inner workings of DJI products that would compromise IP, or patent infringement. DJI is not a sponsor of Tinee9 but Tinee9 is apart of DJI affiliate program to help earn revenue to keep the website going.

Tinee Lesson #1: Series Resistors

Picture of Tinee9: Resistors in Series

Tutorial Level: Entry Level.

Disclaimer: Please have a parent/guardian watching if you are a child because you can cause a fire if you are not careful.

Electronic design goes way back to the telephone, light bulb, powered plants in AC or DC, etc. In all of electronics you run into 3 basic components: Resistor, Capacitor, Inductor.

Today with Tinee9 we are going to learn about resistors. We won’t learn color codes for resistors because there are two package styles: Thruhole and SMD resistor which each have there own or no codes.

Step 1: Materials

Picture of Materials

Materials:

Nscope

Resistor Assortment

Computer (that can connect to Nscope)

LTSpice (software

Below is a link to the Nscope and Resistor Assortment:

Kit

Step 2: Resistors

Picture of Resistors

Resistors are like pipes that allow water to flow through. But different pipe sizes allow a different amount of water to flow through it. Example a big 10 inch pipe will allow more water to flow through it than a 1 inch pipe. Same thing with a resistor, but backwards. If you have a big value resistor, the less electrons will be able to flow through. If you have a small resistor value then you may have more electrons to flow through.

Ohms is the unit for a resistor. If you would like to learn the history of the of how the ohm became the unit named after German physicist Georg Simon Ohm go to this wiki

I will try and keep this simple.

Ohm’s Law is a universal law that everything abides by: V = I*R

V = Voltage (Potential Energy. Unit is Volt)

I = Current (Simple terms number of electrons flowing. Unit is Amps)

R = Resistance (Pipe size but smaller is bigger and bigger is smaller. If you know division then pipe size = 1/x where x is the resistance value. Unit is Ohms)

Step 3: Math: Series Resistance Example

Picture of Math: Series Resistance Example

So in the above Picture is a screen shot of an LTspice model. LTSpice is software that help electrical engineers and Hobby people design a circuit before they build it.

In my model, I placed a Voltage source (ex. Battery) on the left side with the + and – in a circle. I then drew a line to a zig zag thing (this is a resistor) with R1 above it. Then I drew another line to another resistor with R2 above it. I drew the last line to the other side of the voltage source. Lastly, I placed a upside down triangle on the bottom line of the drawing which represents Gnd or reference point of the circuit.

V1 = 4.82 V (Nscope’s +5V rail Voltage from USB)

R1 = 2.7Kohms

R2 = 2.7Kohms

I = ? Amps

This configuration is called a series circuit. So if we want to know the current or number of electrons flowing in the circuit we add R1 and R2 together, which in our example = 5.4 Kohms

Example 1

So V = I*R -> I = V/R -> I = V1/ (R1+R2) -> I = 4.82/5400 = 0.000892 Amps or 892 uAmps (metric system)

Example 2

For kicks and giggle, we are going to change R1 to 10 Kohms.

Now the answer will be 379 uAmps.

Path to Answer : I = 4.82/(10000+2700) = 4.82/12700 = 379 uAmps

Example 3

Now R1 = 0.1 Kohms

Now the answer will 1.721 mAmps or 1721 uAmps

Path to Answer : I = 4.82/(100+2700) = 4.82/2800 = 1721 uAmps -> 1.721 mAmps

Hopefully, you see that since R1 in the last example was small the current or amps was bigger than the previous two examples. This increase in Current means there are more electrons flowing through the circuit.

Now we want to find out what the voltage will be at the Probe point in the picture above. The probe is set in between R1 and R2……How do we figure out the voltage there?????

Well, Ohms law says Voltage in a closed circuit must = 0 V. With that statement then what happens to the voltage to from the battery source? Each resistor takes away the voltage by some percentage. As we use example 1 values in example 4, we can calculate how much voltage is taken away in R1 and R2.

Example 4

V = I * R -> V1 = I * R1 -> V1 = 892 uAmps * 2700 Ohms = 2.4084 Volts

V2 = I * R2-> V2 = 892 uA * 2.7 Kohms = 2.4084 V

We will round 2.4084 to 2.41 Volts

Now we know how much many volts are being taken away by each resistor. We use the GND sysmbol (Upside down triangle) to say 0 Volts.

What happens now, the 4.82 Volts produced from the battery travels to R1 and R1 takes 2.41 Volts away. Probe point will now have 2.41 Volts which then  travels to R2 and R2 takes away 2.41 Volts. Gnd then has 0 Volts that travels to the battery which then the battery produces 4.82 Volts and repeats the cycle.

Probe point = 2.41 Volts

Example 5 (we will use values from Example 2)

V1 = I * R1 = 379 uA * 10000 Ohms = 3.79 Volts

V2 = I * R2 = 379 uA * 2700 Ohms = 1.03 Volts

Probe Point = V – V1 = 4.82 – 3.79 = 1.03 Volts

Ohms Law = V – V1 -V2 = 4.82 – 3.79 – 1.03 = 0 V

Example 6 (we will use values from Example 3)

V1 = I * R1 = 1721 uA * 100 = 0.172 Volts

V2 = I * R2 = 1721 uA * 2700 = 4.65 Volts

Probe Point voltage = 3.1 Volts

Path to Answer Probe Point = V – V1 = 4.82 – 0.17 = 4.65 Volts

Probe Point alternate way of calculating voltage: Vp = V * (R2)/(R1+R2) -> Vp = 4.82 * 2700/2800 = 4.65 V

Step 4: Real Life Example

Picture of Real Life Example

If you have not used the Nscope before please refer to Nscope.org

With the Nscope, I placed one end of a 2.7Kohm resistor in a Channel 1 slot and the other end on the +5V rail slot. I then placed a second resistor on another Channel 1 slot and the other end on the GND rail slot. Be careful as to not have the resistors’ ends on the +5V rail and GND rail touch or you may hurt your Nscope or catch something on fire.

What happens when you ‘short’ +5V to GND rails together? The resistance goes to 0 Ohms!!!

I = V/R = 4.82/0 = infinity (very large number)

Traditionally, we do not want current to approach infinity because devices can’t handle infinite current and tend to catch on fire. Luckily Nscope has a high current protection to hopefully prevent fires or damage to nscope device.

Step 5: Real Life Test of Example 1

Picture of Real Life Test of Example 1
Picture of Real Life Test of Example 1

Once all set up, your Nscope should show you the value of 2.41 Volts like the first picture above. (each major line above channel 1 tab is 1 Volts and each minor line is 0.2 Volts) If you remove R2, the resistor that connect Channel 1 to GND rail, the red line will go up to 4.82 Volts like in the first picture above.

In the second picture above you can see LTSpice prediction meets our calculated prediction which meets our real life test results.

Congrats you have designed your first circuit. Series Resistor connections.

Try out other values of Resistance like in Example 2 and Example 3 to see if your calculations match real life results. Also practice other values too but make sure that your current does not exceed 0.1 Amps = 100 mAmps = 100,000 uAmps

Initial Development of a Medical Device

While on my journey to educate people about electronics, technology, and drones, I came across an idea, which was inspired by the death of a co-worker at my aerospace company during work.

The idea so far in development is a glorified sports watch/band that tracks your heart rate and oxygen stats. Eventually it will include and track a more health stats. All these stats combined will help save the lives of those like possibly my co-worker if place on the patient.

IMG_20180519_215614

IMG_20180519_203836IMG_20180519_215607

Unfortunately, as seen above the proof of concept circuit is bulky and thick. Not very convenient of a product, but luckily this not the end product and very early in its development.IMG_20180519_220906

To start the development process, I have decided to start with the arduino nano platform which I am familiar with. With the arduino platform I am flexible with the software, it is familiar, also there is a lot of libraries out there for the devices I want to use. The devices I have initially picked are a Bluetooth device to connect my phone so the user can read the health stats, a particle sensor, and a battery. Below are pictures with links to Amazon for the modules I used. (no battery in the links)

After putting it all together I was able to get  a heart rate reading sent to my phone via bluetooth. My goal is to get enough money to hire a patent lawyer to patent the idea which I hope to share with you my readers in the future. But for now I will just show the progression of what it looks like and basic functions of the eventual product that will save people’s lives.

Below is a practical use of the device.IMG_20180520_115509