CAL Multirotor Blog

Today, I hosted a MEETUP group - the South Bay Quadcopters.  It was a good time, even though that only 8 of over 85 "members" showed up.  

I got to try some FAT SHARK goggles for the first time.  I was flying my little 6" "pocket rocket" (250 mm quad).  I had a 5.8GHz 600mW transmitter and a Sony HD camera sending the video to the ground. While wearing the goggles gave me a whole new perspective, it was disconcerting because while I could (only) what the aircraft could see, I didn't know where it was in relation to me.

I think that with a little practice, I could quickly overcome my disorientation.  So I'm going to buy some!

I did a test flight of one of my bigger quads (12" props, 6 lbs, full gimbal, FPV, GPS, etc.).  I noticed that when I first armed it, the right rear prop didn't spin.  So I disarmed it and armed it again.  It started this time.  I should have known that something wasn't right and tied it to something heavy and cranked up the motors - but I was at the meetup, so I sent it into the air.  All was fine for a little while.  Then the quad came plummeting to the ground.  At about the same time it hit the ESC controlling the right rear motor was ON FIRE! I ran over and blew out the flames.  I wanted to make certain that nothing else burned. Fortunately, I got there before several hundred dollars of "stuff" burned.

So what happened?  I am convinced that the ESC was defective and led to the mess. The ESC was an expensive, (supposedly) high quality one.  Of course, it was made in China - but they all are.  I have attached a picture of the burned ESC, and another picture of a new one.  Note how the label calls it "Bulletproof". I somehow question that designation.

At the MEETUP 2 weeks ago, I saw some of the participants flying FPV with Fat Shark goggles.  I asked if I could try on a pair, and one guy let me.  We changed the transmitter channel on my little 6" (prop - 250mm frame) quad and got a picture. I put my little quad in the air, and wow!  It was neat, and it was scary.  Neat in that I could see everything in front of the craft.  Scary because I had no idea where the copter was in relationship to me. I need some experience before I'll be anywhere as good as several of the people there.

The fact that I wear +3 glasses for reading is also a problem:  The Fat Shark goggles were designed for people who don't wear glasses - or wear contacts.  When I took off my glasses and put on the Fat Sharks everything looked very blurry.  But the possibility of flying around obstacles and controlling the craft like a fighter pilot intrigued me.

So, I bought a pair of Fat Shark Dominator V2 googles and a "beta" radio, which allows me to tune to the same frequency as my BOSCAM transmitters. 

I went to Rite-Aid and bought a pair of +3 reading glasses.  I removed the lenses and cut them down to a suitable size for the Fat Sharks.  I put the lenses just behind the Fat Shark lenses and took a peek.  Although I haven't installed the added lenses permanently, the preliminary results are promising - very promising.

I was eager to try out my new FPV goggles.  So I went to the park and put my little 6" (prop) quad in the air.  The video was great.

But I had no idea of where I was in space. I so I reached up to remove my goggles.  

At that time, my remote control transmitter fell out of my hand.  The lanyard around my neck caught it, but not before it jammed the throttle to max.  

Did I ever mention that little quad climbs AWFULLY fast?  By the time I got my hands back on the controls, it was nearly out of sight.

Crisis #1 averted!

I tried again.  I put the glasses on and had a better Idea of where it was this time.  At least for awhile.  I went higher and higher.  So far so good.  Then I brought it back down.  But it comes down just as fast (probably faster) than it goes up.  At one moment I was at 150' altitude.  About a second later, I was at 6".  At the rate I was falling, the throttle did no good.  In fact, it was the wrong thing to do, since I hit the ground at full throttle.

Crisis #2 NOT averted!

I broke an "arm" on the frame.  Fortunately, I can print another.  But it is still a hassle to fix.  At least 2 hours of work.

It is going to take me a little while to learn to fly with my new goggles.  Hopefully, I won't break too many more things before then.

I balance my props dynamically, so they generate very little vibration.  Still, nothing is perfect, and there is always the vibration caused by AERODYNAMIC unbalance that is hard to correct.  Aerodynamic unbalance occurs when one blade has more lift than the other. As the blade rotates it pulls on the motor shaft in a circular motion.  This twists the motor mount in a sort of "Calypso" movement and excites resonances.  

The bottom line is - it is impossible to stop every vibration at every possible motor RPM.

I bought a decent gimbal on-line for about $55.  It had the little black vibration dampening "balls".  It also had just a flat bar for the camera to sit on.  The flat bar had two slots for a strap that connected to a ring that went around the lens.  The problem is - the slots were in a place that put the USB port of the GoPro against the "pitch" motor.  It would be impossible to connect the camera to a video transmitter.

So I printed a different camera holder. One that wraps around the camera on 5 sides. And it leaves the USB port accessible.

I flew the gimbal, and it worked well to hold the camera level, but there was too much "Jello".  I had some super-soft dampening balls that I had bought from Hobby King.  I put those on the gimbal and tried again.  This time there was very little wiggle in the picture.

Moral of the story:  Get some very soft dampening balls of various sizes.  They will come in handy.

I was doing some upgrades on one of my bigger quads (12" props, 910KV motors, 4Cell battery), and I was watching the current meter climb past 70 Amps as I ran up the throttle.  70A X 16V = 1120 Watts!   And I was feeling the wind blow EVERYTHING in the room that weighed less than 1b. - screwdrivers, knives, a cereal bowl that I had been eating Cheerios from.  And of course, every paper in the room.

And as I was working with the motors, I realized just how much torque they had.  These are not little motors: They are 36mm diameter, with a magnet height of 18mm.  

And then I used my optical tach to find out just how fast they were spinning.  6,920 RPM!   Nearly 7,000 RPM on a 12" prop. These motors and props could easily cut an arm or leg to the bone, or cut a jugular vein or nearly rip off someone's face.

The all-up weight of this quad is nearly 7 lbs.  Imagine if it was at 400' and fell.  Not a pretty sight - even if it didn't hit a person.  It would put a large dent in someone's car.  It might even go partway through someone's roof.

And the 4Cell battery is 5Amp hours (5000mAH at 16V).  The battery is a "40C" type, meaning it will output at least 5Amps X 40 = 200 Amps during a short circuit.  200A X 16V = 3200 Watts.  That will get the battery (or anything that is carrying the current from it) really hot, really fast.  The lithium used in the battery is flammable.  You get the idea.

If my quad fell on someone's roof, I might not know exactly where it landed. If it shorted the battery in the crash (fairly likely), then SOMETHING is going to catch fire.

While the little 250mm and smaller "racer" quads are fast, they have a much smaller motor, smaller props and smaller wiring (which will hopefully act as a fuse during a short circuit), so they aren't nearly so dangerous - although I won't state that they are "safe" by any means.  

If you fly big, heavy craft like I do.  Please keep all of this in mind.  A pic of the quad I was working on is below.

From time to time, I have had quads simply "fall out of the sky" for no good reason.

Today, I took a small quad out and armed it.  When I gave it a little throttle, all the motors started spinning - except the right rear one.

It just jerked a bit.  I dis-armed the craft and armed it again.  Same thing.  

I looked at all the connections. They were tight, but I knew something was not right.  If one of the two wires that feeds battery power to the ESCs was loose, the motor wouldn't spin at all, but if one of the three wires that went between the ESC and the motor were loose, it would jerk - just as I had observed. 

I got out my ohm-meter and did some checking.  I had earlier fashioned some special probes for my voltmeter that consisted of two MOLEX style female crimp pins that fit over the meter probes, but instead of crimping wires into "wire end" of the MOLEX pins, I crimped (and soldered) two medium-sized sewing needles.  The needles allow me to probe very small parts, and also to puncture insulation without damaging it.

Two of the 3 wires between the ESC and the motor had very good connection.  The third was flakey - I moved the wire back and forth and sometimes I got good connection, sometimes not. The problem seemed to be the 3.5mm bullet-style connectors themselves. But they were tight.  I inspected them carefully and noticed one thing:  The expandable parts of the male connector freely rotated on the rest of the connector.  The connection between the expandible part and where the wire was soldered was not a good electrical connection.  I replaced the connector with what is normally considered to be a more "crude" type and got a great connection. 

A picture of the BAD type is shown below

Note that the expandable part is a separate piece that is put onto the connector.  Then the end of the connector is "mushroomed" out to hold it in place.  The key item is that the expandable part has no guaranteed connection to the rest of the connector.

A picture of the GOOD type is shown here:

This connector is one piece.  the 4 "fingers" are attached to the base and do not rotate.

I was working on the details of my Santa Cruz Project and I was looking for some different motors.  By chance, I found a deal on line for some little 1804 (=tiny) motors.   $25 for 4, shipping included!   So I bought them.  I had a spare 250mm quad frame lying around, and I certainly have extra receivers, controllers (KK2, NAZE32, MiniAPM, CC3D) that I could put on it, so why not?  The only other thing that I would need would be props, and those are available in Santa Clara for less than $3 each.

I got the motors yesterday, and put them together with a KK2 controller, 6" props, 3Cell batteries, 30A ESCs (don't need them that big, but that is what I had.

I should mention that the motors are ZMR/RCX 1804 rated at 2300KV

With virtually no effort at all, the craft flies - and flies well.  I'm really impressed.

When I go to a new town (like New York City), I try to check out at least one local hobby shop to see what they have.  

I'm always disappointed.

Why?  Because most all have the same stuff they have had for years.  The same WWII replica plane or conventional helicopter.

They generally have few multirotors. But when I look around, I see multirotors being sold at Fry's electronics, they are in the news all the time, there are now 3-4 times (by my estimate) more MEETUPS that involve multirotors compared to conventional R/C.  

I'm certain that one reason for the popularity is the fact that you don't need a landing strip for a multirotor.  And they are easier to fly than a regular helicopter. Also the fact that you can buy a tiny, entry level craft for under $50 and "graduate" to bigger craft with cameras later.  The "cost of entry" of getting into quadcopters is cheaper than buying one of the old control-line airplanes that I tried to fly as a boy. The difference is dramatic if you consider inflation. And that control-line plane didn't do anything but go up and down while it was flying in circles around me. Boring!  

I bought some ESCs from China recently.  They were pre-programmed for LiPO batteries - but for defaults had very slow response to input changes, brakes ON and a "hard" cutoff at 11V.   Not something you would want in a multirotor!  And to top that off, you couldn't re-program it to be useful with a multirotor without buying one of their programming cards.  

And I saw a motor that would be great for a multirotor on EBAY.  It was at a great price, so I went to bid on it.  But the only quantity I could buy was ONE.  In order to buy more, I had to buy the one item 4 times. I tried to get the Chinese merchant to bundle the shipping, but they told me they couldn't do that (because they were already packaged for shipment in prepaid shipping boxes).  So now, the 4 motors would have a shipping cost of $40. I didn't place the order. Why don't they "get it" and sell these things either as one OR four (or maybe 5, so you have a spare)?

And when I'm at a hobby shop in the US, and I ask why they don't have more multirotors. The reason they often give is 

"We don't have that many people asking for them".

No wonder.  I often use a statement that probably fits well here:

A Chevrolet dealer might think that very few people want Fords, because no one ever comes in and asks for one.

I built a motor and propeller tester last week.  Here is video showing how it works if you should decide to build something similar.

I plan on characterizing many motor/prop combinations, and I'll publish the results starting in a week or so.

My wife and I very recently went to Switzerland.  Earlier this year, I built a small, foldable, 10" prop quad just to take on the trip.  At the last moment, I decided against taking it mostly because I had no idea of the laws in Switzerland regarding drones.I also thought that it would be just one more thing to look after and haul around as we went from city to city.

I made a bad decision.  Having a camera in the air would have been fantastic in such a beautiful country.  I was close enough the the Matterhorn that I could have landed on the summit.  I was close enough to Jungfrauyoch (highest mountain in Europe) to land in its summit as well. My control range is about 4 miles (my 2.4Ghz transmitter is boosted to 2 Watts), and I have a 2W 5.8Ghz video transmitter my helical antenna and FatShark googles to send video from the Sony 700TVL camera.  That has about a 5 mile range. I have a 2-axis gimbal and GoPro  mounted on that quad as well.

It will fly about 12 minutes going maximum horizontal speed of 35mph.  Its climb rate (at sea level) is about 2700'/min. My first thought is that If I took off at a point 3 horizontal miles from the summit and 7,500' lower in elevation, I could probably do it.  My thinking went as follows:

First, to make the calculations easier, I'll just plan to go straight for 7,500' first.  That will take 4 minutes (the climb rate will be reduced because of the altitude)  Then I'll go 3 horizontal miles at 35mph, which will take a total of 5 minutes and 8 seconds at sea level, but because I'm not at sea level, I'll add time due to the altitude. So lets say it will take 6 minutes to travel the 3 miles.  This gives a total of (4 + 6) = 10 minutes.  The return trip will be much easier, since the craft will be running at a lower-than-hover speed ( it will be coming down at a slope).  

But with only 12 minutes of 80% throttle airtime, it doesn't look like I'd be guaranteed to get "home" using the above scenario. So I thought that If I moved one mile closer to the mountain top, I could cut the time to get to the summit by 2 minutes.  On the return trip, the craft would have to go less horizontal distance and would have to come down faster.  This reduces power usage even more. 

So, if I go back to Switzerland, I'm going to take my foldable quad, hike to within 2 miles of the top of the Matterhorn and get some great pictures.