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New Bat Bone setup, battery position & hot motor - PICS

#1
Here's my setup:
HK 30A ESC's w/simonk, Turnigy 2730-1300kv motors, 8x4.5 props, 2350mah 20c batt.

I've had the battery near the front (side-to-side, pic 1) of the copter for a several flights and then saw that placing the battery lengthwise (2nd pic), closer to the back may be better.
For my short time with the battery as in pic 2, I thought it flew better.
Both front motors do not get over 110[SUP]o[/SUP]F.
My battery in pic 1 position, tail motor gets about 130[SUP]o[/SUP]F.
Battery in pic 2 position, tail motor gets about 160-170[SUP]o[/SUP]F. Both, I think are too hot.

I'm wondering if anyone knows why this may be happening. Should I try a different prop/motor? And, what battery position is better?
Thanks,
JD
2013-07-14 18.17.21.jpg 2013-07-14 18.14.34.jpg
 

earthsciteach

Moderator
Moderator
#4
I can't imagine that battery position is the reason for the temp difference. Just thinking here... Did any wires get looped around the esc wiring?

Does the hot motor sound any different than the others? I'd pull it apart to make sure its not rubbing on anything Check the stators to see if there are any spots where the magnets are rubbing. Check the bearings. Make sure there is no dirt in the motor.
 
#5
I'd say the battery position is the main reason for the temperature difference...

Think about it, on a tricopter, the back motor is constantly spinning at a little higher rpm than the front motors, because it is tilted to keep the yaw constant. Now, when you shifted the weight a little backwards, that rear motor has to work a little more than before, or spin a little faster, thus the higher temperature.

Best battery position? The one that gets your tricopter CG true.

Make sure your bearings are good and lubed!
 

colorex

Rotor Riot!
Mentor
#9
how do you find true CG? just balancing the tri on the tip of your fingers?
This is a question that still eludes me. On a normal quad it's easy just draw a line between opposing motors. But on a tri it's different I guess. I mean it's the point from where you have equal distances to all the motors, but how you find it I can't tell you.
 
#11
how do you find true CG? just balancing the tri on the tip of your fingers?
Something close to that, the lateral balance is easy to check, for the front to back balance I usually use a round cardbord tube, or you can use the top of a chair back rest, use your imagination :)

This is a question that still eludes me. On a normal quad it's easy just draw a line between opposing motors. But on a tri it's different I guess. I mean it's the point from where you have equal distances to all the motors, but how you find it I can't tell you.
On a tricopter should not be harder ;)
On a normal tricopter, draw an imaginary line between the front motors (you could use a piece of string here, a line, a wooden dowel, etc). The CG is at a third up the line that goes from back motor perpendicular to this imaginary line (or two thirds down from the back motor). Even a T copter should have the same characteristics.
 
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Cyberdactyl

Misfit Multirotor Monkey
#12
You've got my curiosity up.

Tonight I'm going to overload one of the motors by placing some mass way out on an arm and see if I get a large increase in battery temperature and if that particular motor's temp also increases.

Without seeing the results before hand, my guess would be the particular motor under the extra load would run hotter, but the battery temp being so terribly high, sounds very odd indeed.
 

colorex

Rotor Riot!
Mentor
#13
You got it, Andre. The cg should be the point equidistant do each motor, assuming the motors are arranged in an equilateral triangle. If not, you can use this:
http://www.dummies.com/how-to/content/how-to-pinpoint-the-center-of-a-triangle.html
Yeah that is the centroid. Silly me, I knew how to do that.

What bugs me is how do you calculate the centroid on a quad like the TBS Disco? I've found several possible methods but never tested or proved any.

My most intricate method was probably this one:

"Divide the four-sided polygon into two triangles by drawing a line between two diagonally opposing motors. Find the centroids. Then repeat step one but with the dividing line between the other two motors. Find the centroids. Now you have four centroids, draw lines between them that cross and that is the point."

I also tried balancing the torques along the roll-pitch axes but it didn't quite work out.

Another method which is more likely to be correct and is also based on torque calculations is to draw lines between the two front motors and the two back motors and then draw a line between the midpoints of the previously drawn lines. Center of this line would be the balance point of the pitch axis. Rrepeat the process for roll axis.

Again, all these are just theories I've formulated.

Untitled101.jpg
 
#14
earthsciteach,
Would you clarify the "wires wrapped around the esc's. I have a bat bone, so I attempted to hide my esc's in the frame. I' don't know if this a contributing factor.
btw, last flight motor got much hotter an started to perform badly.
PIC of esc locations. Back/tailrotor is to the right.
2013-07-15 13.56.38.jpg
 

earthsciteach

Moderator
Moderator
#15
I doubt it is anything to worry about. I was wondering if a wire could be looped around the motor wire inducing some weird current. I had an esc catch on fire once and I think it may have been due to that reason. But, I'm no electrical guru, so I very well could be wrong.
 

Carbon

Elemental Madness
#17
^true, ish. With a tricopter you want it to be a little bit nose heavy. Mostly because you get better tail response and the front two motors support more of the load.
 

Tritium

Amateur Extra Class K5TWM
#18
Why would anyone want to calculate anything when it is easier and absolutely accurate to MEASURE!
Calculations are fine for design but measurements are for the REAL WORLD and frequently do not match calculations!
C.G. ---- The point of balance. The chair back, knife edge or tube approach is best on small craft like the multi's we fly.
High temps can damage NdFeB magnets very quickly unless they are a high temp version and I doubt that the better magnets get used in cheap motors.

Thurmond