Pumpkinguy
Member
IMO their numbers lean heavily towards "optimistic".
KDE vs T-Motor -- Picking a Motor Based on Spec Sheets
- Thread starter econfly
- Start date
IMO their numbers lean heavily towards "optimistic".
Pumpkinguy
Member
Based on my tests the 55 amp is good for 16" max prop. Anything more you should use the 75+
Pumpkinguy
Member
A manufacturer can recommend anything they want but what is so magical about kde bearings that they last 5x's longer? I'm repeating myself here for the people that don't know my background but. I was a "Certified Bearing Specialist" for 20 years. Servicing various industries. My kde motors came with NMB bearings. NMB IMO is not the best quality.
Motopreserve
Drone Enthusiast
I thought the advantage was an extra bearing helping reduce the load/wear per bearing.
I am admittedly NOT a bearing specialist
I am admittedly NOT a bearing specialist
Pumpkinguy
Member
I thought the advantage was an extra bearing helping reduce the load/wear per bearing.
I am admittedly NOT a bearing specialist
Tmotor does not publish their motor bearing sizes but I believe they use 2 larger bearings vs 3 smaller ones. The whole idea here is to increase the radial load capacity.
Motopreserve
Drone Enthusiast
Pumpkinguy
Member
The kde 4215 and tmotor u7-490 are both rated for 3kg of thrust.
Some quick math tells me the u7 has a full 1/3 more stator surface area.
So, how is it possible the kde's are equal in output torque? Are they 30% more efficient?
Some quick math tells me the u7 has a full 1/3 more stator surface area.
So, how is it possible the kde's are equal in output torque? Are they 30% more efficient?
Pumpkinguy
Member
I will point out that based on my experience with the kde 4215 it is a perfect motor for 2kg thrust with a 16" prop. It will run cool at that load.
It starts to heat up around 2.5kg's using 18" props. I have not tested it with 17's as I didn't have them.
I believe the 5215 motor is a better choice in the 2.5-3kg range as is the U7's.
Now the u7's have other issues. The t80a apparently runs crazy hot at the higher loads. Hot enough to melt the heat shrink tubing off but no reported crashes from this. If I go that route I will be adding 25x50mm heat sinks and 25mm fans.
It starts to heat up around 2.5kg's using 18" props. I have not tested it with 17's as I didn't have them.
I believe the 5215 motor is a better choice in the 2.5-3kg range as is the U7's.
Now the u7's have other issues. The t80a apparently runs crazy hot at the higher loads. Hot enough to melt the heat shrink tubing off but no reported crashes from this. If I go that route I will be adding 25x50mm heat sinks and 25mm fans.
fltundra
Member
I never said KDE's have the best bearings
. Just sharing my experience. My tiger 470kv's that i once owned had bearing play within ten hours, to me completely unacceptable. Yes, NMB abec 7's are not the best, but so far better then what was in the tigers, and to top it all off the motors weren't even close when it came to vibration levels.learningrc
Member
For general sizing of motors, volume is more important than surface area. Some people use rotor volume and some use stator volume, depending on the type of motor and a number of other factors. D^2*L is often used to size motors.
Anyway, according to this the KDE motor is rated at 1375 W and according to this the Tiger motor is rated at 1300 W. Those are both continuous power ratings. That is closer to a 5% difference. I couldn't find any info on the outside diameters or lengths of the stators or rotors so I'm not sure what the D^2 * L is on either motor.
Also note that ratings are determined by the thermal capabilities of the motors, not the efficiency. If a motor has better insulation or dissipates heat better, then you could have a higher power rating while still having worse efficiency.
econfly
Member
Your experience has definitely influenced my thinking. It is just terrific to have a specialist in bearings posting here. Thanks a lot.
SchrodingersCar
Member
Sorry, not trying to sidetrack the thread, but quick question I never got resolved about this frame - It seems to be a really popular choice, but are people worried about performance due to the low CG? A flat rig with a heavy camera and gimbal hanging off of it is enough of a "flying pendulum" as it is, the z-arms look to drop the weight distribution even lower? Or is that not a big deal??...
SleepyC
www.AirHeadMedia.com
The weight on the bottom and the lower CG usually makes for a more stable rig. I've never had a pendulum issue.
SchrodingersCar
Member
As I understand it you gain stability, but lose maneuverability.
My large rig can sometimes "swing" a little with a heavy camera if stopping fast or attempting maneuvers involving more pitch and roll. Maybe I just need to tune the gains more, but I'd figure minimizing that effect would be better for efficiency and maneuvers anyway...
My large rig can sometimes "swing" a little with a heavy camera if stopping fast or attempting maneuvers involving more pitch and roll. Maybe I just need to tune the gains more, but I'd figure minimizing that effect would be better for efficiency and maneuvers anyway...
SleepyC
www.AirHeadMedia.com
Probably true, but for most AV work, the smoother the better. I have never had an issue where I couldn't maneuver fast enough to get the shot.
Motopreserve
Drone Enthusiast
You tested it???
Motopreserve
Drone Enthusiast
Bummer. You'll do a write up soon? I'm curious to see the difference in your numbers to the ones provided by KDE.
Pumpkinguy
Member
In my previous career when I was selecting motors, gearboxes, chain, belt and gear drives for industrial applications I could always count on
The specific drive to work as intended unless I made a bad calculation. (Which I didn't because I tripple checked numbers)
I made many mistakes selecting motors and esc's for my hex. Was I at fault or were the numbers a little off???