Hot Motors!

[GlassKnees]

Okay, so this isn't my first build, but it's a scratch build - an Elev-8 built up from spare parts lying around - I call it my Frankenstein quad:

The frame measures around 28" or 711 mm. and AUW is around 1.4 Kg. The motors are Tarot 4006 620 Kv with 13"5.5 pitch carbon props. I'm using a small 3s lipo to power the video transmitter and Feiyu-tech mini 3D gimbal. Main power is a 4S 5500 mAh lipo.

I did a short test flight yesterday - hovering around for less than 2 min and landed - the motors were hot to the touch. Ambient temp was moderate - mid 70's (F.) fairly high humidity and light breeze. I fear that I'm overworking the motors, but specs seem to indicate max thrust is 1.3 Kg, so four motors should be adequate.

Also, endurance is an issue - previous flights only last around 6 min before the voltage failsafe kicks in. I tried two lipos in paralle, but I think the weight was too much - motors were reallyl hot after only a minute.

So, I'm shopping around for replacement motors, such as the T-Motor Antigravity 4008: http://www.rctigermotor.com/html/2015/Antigravity_Motors_0212/289.html

Besides the cost, I'm chafing at going from 4s to 6s power. So, I'm asking for advice - any suggestions?

 

[mozquito1]

Reset your pids, sounds like the I gain is high or low. I don't build that big so good luck.

 

[GJH105775]

When you come to your final build you should not be that close to your max thrust. For racers normally you want a minimum of a 1:3 thrust ratio. I like to keep my racers around a 1:5 thrust ratio (Weight:Thrust). These numbers are for racers which need to have a lot of acceleration, and be able to change directions a lot faster. For a bigger camera quadcopter most people suggest a 1:2 thrust ratio though you can achieve stabilization fly on at least a 1:1.2 as most flight controllers suggest 10% just for stabilization, but then you need to be able to increase altitude and have the overhead to pitch, roll, and yaw.
22
If you are fine with more docile flight you will probably need at least a 1:1.5 for your build, though I would suggest a little better to get nicer flight times.


It might prove cheaper to turn it into a hex or octo than to get four newer, nicer motors.

So when you say 1.3 you mean a piece or all together? Could you give a video of it's flight and maybe some blackbox data if available?

 

[GlassKnees]

For 1.3 Kg thrust, I assumed that the spec meant for a single motor. If this is the case, then 2.6 Kg thrust should be fine for my aircraft. Since it is intended to be a video platform, I want a docile, stable aircraft. The only video I captured was onboard stabilized video from the GoPro, which wasn't particularly helpful.

I actually have two Elev-8s that are set up pretty much the same, except the other has a Tarot two axis gimbal and it, along with the video transmitter draw power from main battery (via spare ESC ports on the autopilot).

I have some log data, but don't know how to interpret some of the parameters. Are you experienced in interpreting APM log files?

 

[GJH105775]

For 1.3 Kg thrust, I assumed that the spec meant for a single motor. If this is the case, then 2.6 Kg thrust should be fine for my aircraft. Since it is intended to be a video platform, I want a docile, stable aircraft. The only video I captured was onboard stabilized video from the GoPro, which wasn't particularly helpful.

I actually have two Elev-8s that are set up pretty much the same, except the other has a Tarot two axis gimbal and it, along with the video transmitter draw power from main battery (via spare ESC ports on the autopilot).

I have some log data, but don't know how to interpret some of the parameters. Are you experienced in interpreting APM log files?

Never tried for APM, but might be able to recognize some PID problems with it as they are not likely too different from Clanflight logs .

 

[GJH105775]

Found something to help with determining for you:

 

[Jackson]

For 1.3 Kg thrust, I assumed that the spec meant for a single motor.

It is. This chart shows a bit higher, same prop.

Here's a test, he may have slightly higher kv as he claims 680, same prop.

Do your ESCs feel hot? Are you sure about your AUW? 1.7kg sounds light, your battery alone is 500+ grams.

That said in his test @ 50% throttle he got 580 grams of thrust X 4 = 2.32 kg.

 

[GlassKnees]

I weighed my copter earlier today to confirm, and to my astonishment, it weighed in at 5 lb, not 3 as I originally stated. So, it's not surprising that my Tarot motors were getting hot.

Looking at motors with more power seem to require 6S lipos, but I'm pretty much constrained to 4S, as I have an APM power module plugged inline with the battery and power distribution harness and the power module limitation is 4S. I don't want to mess with redoing power distribution and splicing resisters, etc. to lower voltage to the power module, so I'm restricting my search to a motor that can handle a 2.3 KG AUW quadcopter.

Right now, I'm looking at the T-Motor MN3110 KV780 motor: http://www.rctigermotor.com/html/2013/Navigator_0910/35.html

According to the specs. at 4S and using 15"propellers, I can expect to get thrust to weight ratio of 1.6 @75% throttle and 2.1 @100%. If the numbers are true, that should be enough for my needs.

 

[Jackson]

so I'm restricting my search to a motor that can handle a 2.3 KG AUW quadcopter.

What's your approximate throttle % for a hover?

It seems that your current setup should work.

That said in his test @ 50% throttle he got 580 grams of thrust X 4 = 2.32 kg.

Your numbers aren't all that bad. If for the motors we use 1.4kg X 4 = 5.6kg. So basically that's 2.45X your AUW. Can you lighten your beast up a bit?

 

[GJH105775]

What's your approximate throttle % for a hover?

It seems that your current setup should work.


Your numbers aren't all that bad. If for the motors we use 1.4kg X 4 = 5.6kg. So basically that's 2.45X your AUW. Can you lighten your beast up a bit?

Good point also how hot is hot? Your build in theory should be able to handle this. Bad PIDs could be overworking the motors too.

 

[GlassKnees]

I will have to fly again to take not of throttle % for hover. Will examine PIDs...

 

[GlassKnees]

Have some news since I posted last.... I tried a short flight with one of my two video platforms - and again the motors were really hot. It was calm air just after the sun went down and the air was cool. I decided I don't want to risk a crash so both copters are grounded, pending motor replacements.

I checked the specs on the new DJI Matrice 200 and found that it weighs about the same as my modified Elev-8's - found that the motors they use are essentially T-Motor MN3515's. I was all set to buy them when I discovered 7 t-Motor MN3520's for sale on Amazon for $46!!! These are $110 motors! The seller has had them for awhile and weren't selling so he discounted them to get rid of inventory.

Given the specs, these motors should provide enough thrust and I won't have to worry about overheating them. But I have to go from 4S to 6S lipos. This is a problem because the power module that supplies 5V to my APM flight controller can't handle 22 V. So I will have to use a 5V BEC to power the flight controller and replace the power module with a small current/voltage sense board that samples the voltage - will plug into APM and recalibrate it so I can have reliable voltage monitoring during flight.

Will have to get something like a 10000 - 15000 mAh 6S lipo and a suitable charger.

 

[GlassKnees]

Today, I installed one of the T-Motors on my quad. I was concerned about having mounting holes that would match the motor to the mount, but there were four holes that matched. I connected the copter remotely to my computer, via telemetry, and ran a motor test to check the spin direction and then I secured the motor/ESC leads with a zip tie:

I had previously installed a 5V BEC which I will use to supply power to the APM flight controller. I am waiting on a voltage sense board to arrive which I will install in place of the APM power module - the sense board will provide the APM with voltage/current info from the 6S lipo and trigger the voltage failsafe if the battery voltage drops too low.

I hope to have it ready for a test flight in a week or so.

 

[GlassKnees]

Latest Update 5/01/2017: I installed the T-Motors on Frankenstein today and I received the 16000 mAh 6S lipo I ordered from GetFPV - it is a monster! I put it on my APM #2 ship, which will be the first to test the new motors. I cannot power up the aircraft yet as I need to remove the APM Power Module and replace it with a voltage/current sensing module that is still in transit.

This aircraft is really heavy and the battery barely fits underneath:

 

[GlassKnees]

Before I can power up the ship, I need to remove the APM Power Module as it's max voltage tolerance is 16V. In it's place, I will use a 5V BEC to supply power to the F.C. and use an Atto Pilot Voltage/Current sensor to provide the APM with voltage and current info in order to trigger the voltage failsafe should I let the battery pack run down too low.

The Atto Pilot sensor is a small circuit 0 I ordered two from Sparkfun.com out in Niwot, Colorado:

I had to solder leads for the battery on one side and leads to the power distribution on the other. I also had to solder the small ground, voltage and current leads:

I need to get some shrink wrap for the circuit board and crimp servo connectors on the ends of the small leads before I can install it on the aircraft.

 

[GlassKnees]

Latest update: 5/16/2017...

The aircraft looks like some sort of pregnant spider with the huge 16000 mAh lipo hanging underneath. It basically rests on the battery pack! I've done a few short test flights - it is unstable and tricky. The first flight was under windy conditions - a gust came along and the aircraft yawed 90 degrees, facing me and drifting with the wind backwards towards my neighbor's house. I had to set it down quickly - a hard landing which popped part of the gimbal off the rubber balls and the battery pack was dislodged but remained connected to the aircraft. No damage.

I put it back together and waited for a calm morning. The 2nd flight was not much better - very twitchy. Landed safely in the grass.

I decided to lower the pitch/roll response in Mission Planner and tried a 3rd flight, again under calm conditions. Still twitchy but a little better. Put it in Loiter mode which was okay except it started drifting downwards and I had to goose the throttle a tad. Landed safely.

I've got to do something about the landing skids. Decided to install the skids I salvaged from my totaled Tarot FY680 Pro. The problem is there is no way to mount them on the Elev-8 chassis. I bought a piece of 1 1/4" wide, by 1/16" thick aluminum stock, so I can cut into squares and drill four holes in each corner; using these I can mount on one side of the bottom chassis plate and mount the landing gear underneath and secure with screws/nuts.

But I need to drill precision holes. Looking at a Proxxon Micromot MB 140/s Drill Stand, but it's $64 plus anther $130 for the drill! So, for the time being, things are on hold.

 

[GlassKnees]

Latest Update and bad news....

I just completed fabricating mounting plates for the landing skids and installed them. The aircraft is now completed:

You can't see it very well from this angle, but the 6S lipo is installed and there is plenty of clearance. But there is bad news.
The total weight of the aircraft (10 lbs) is supported by the two landing skids which are attached to the bottom chassis plate; it is flexing due to the strain:

I don't think that this is safe and I'm going to have to scrap it. I think I will have to build a new aircraft and transfer all the components over.

 

[Jackson]

I don't think that this is safe

I don't think it's balanced, way too ass heavy. More the battery forward till it sits level.

 

[mozquito1]

10lbs bloody hell. From a 100' drop that weight will double. Err let me know the day you maiden it. I'm off to the kola deep.

 

[GlassKnees]

I don't think it's balanced, way too ass heavy. More the battery forward till it sits level.

I was in a hurry when I snapped the photo - it looks unbalanced because I didn't hold the camera level. It could indeed be a tad unbalanced as I didn't check C/G when I attached it for the picture.

AS for it being too heavy, well, I've read that a rule of thumb (or as our POTUS would say - rule of covfefe), the battery should make up half of total weight. Given that the aircraft weighs 4.5 lbs and the lipo weighs 5, then I'm within the RoT. For a 5 lb lipo, what would you expect an aircraft to weigh anyway???

The thrust from these motors is sufficient as well as the current draw and with a 16000 mAh lipo I can expect 20 - 25 min. endurance.

At any rate, I'm thinking of buying a Tarot 650 Sport carbon frame and transfer everything over to it. I can get one online for around $85.