??Help??

[Michael]

Hi guys i have built my GB motor and have got a little problem, the motor turns but there is some friction as the motor heats up and i can hear the motor grinding. One place that it is grinding at is on the in inside of the cap where the shaft comes through the can. The bearing shaft is rubbing and causing a 'ring' mark on the can should i just place a washer in there to lift it of the can? secondly there is some slop in the can for example when the motor is assembled i can feel a slight 'wobble' in the can and shaft is this normal if not what can i do to stop it? I am going to go and reglue some of my magnets as some of them have departed from the can, i guess thats because of the heat from the fiction.

[Jay C]

Hi guys i have built my GB motor and have got a little problem, the motor turns but there is some friction as the motor heats up and i can hear the motor grinding. One place that it is grinding at is on the in inside of the cap where the shaft comes through the can.
Ok, how could this be. If you look at the cutaway photo I've attached (and in the tutorial) it's hard for me to see how you are getting any rubbing unless:
1. You are not using a shaft with an integral washer
2. Your can is bent
The bearing shaft is rubbing and causing a 'ring' mark on the can should i just place a washer in there to lift it of the can?
It would be better to use a short sleeve that only touches the inner race of the ball bearing to reduce friction. A small sleeve of brass with an ID of 3mm.
secondly there is some slop in the can for example when the motor is assembled i can feel a slight 'wobble' in the can and shaft is this normal
This is bad. Any wobble at speed = vibration = wasted energy = greater chance for magnets to rub = friction = heat = dead magnets. Worst case it that it will tear itself apart when a magnet grabs on a tooth.
if not what can i do to stop it? I am going to go and reglue some of my magnets as some of them have departed from the can, i guess thats because of the heat from the fiction.
Not a good sign. I have used a jacobs check to reform the inner lip on the can (with the shaft removed) and then reinstalled the shaft to coreect wobble ... but I don't feel too confident in your magnets anymore :( sorry.

Jay

[Michael]

Ok Jay C thanks anyway, I think i will just order a couple more motors and have another go at some more, the more practice the better i suppose! :-) Anyway once again thanks very much, best regards,

Michael

[ibldrc]

FWIW, I too had the same friction problem on my first motor (just ran it last nite).
The brass was touching the can just in front of the plastic washer.
I lightly sanded the brass till it was clear, and it was fine. No idea why it happened, but it was not hard to find and fix.

[Jay C]

FWIW, I too had the same friction problem on my first motor (just ran it last nite).
The brass was touching the can just in front of the plastic washer.
I lightly sanded the brass till it was clear, and it was fine. No idea why it happened, but it was not hard to find and fix.
Well, look at the cut away and you might see how it can happen. The bell is just stamped out of thin steel. It doesn't take much force to warp it. If you didn't support the top of the bell when pressing the shaft, or the shaft was not perfectly perpendicular then a slight skewing can occur.

[flyerdude81]

I just completed my first GB motor (1 stator, 18 turns of 26 wire, Wye, 5x4x2 magnets, ball bearings in carbon fiber tube). The good news is that it works! The less good news is that sometimes its coils get quite hot, and some prop combinations work only slightly. I tested it on my bench last evening with various propellers (7x4, 9x4.7, 10x4, 11x4.7). Full throttle on the 7x4 was easy, and pretty smooth. The 9x4.7 caused it to struggle with rpm falling at high throttle settings. The 10x4 and 11x4.7 just didn't get much speed at all, with high throttle settings simply stalling the motor.

My question is this: is this behavior due to inaccuracies in setting the magnets, insufficiently compact windings, the way I held my mouth, or some combination of all? It would be good to know how best to approach my next attempt, and make a more reliable product. The database seems to imply that large diameter props should work on this motor, although it might be somewhat inefficient. Thanks for whatever you can do to straighten me out.

[Jay C]

No, this is due to a "locked rotor" condition and you trying to "haul a boat with a VW Beetle". The torque requirement of bigger props is too much for the wind you have ... like trying to start a car in 3rd gear.

Make sense?

[Q]

like trying to start a car in 3rd gear.

Hmmmm, where have I read that before?? :lol: :lol: :lol: :lol: :lol:

[flyerdude81]

Thanks for clarifying this. It does, indeed, make sense; I simply am not familiar with the locked rotor situation. Is this due to the fact that we don't have sensors? In other words, the controller simply sends rotational instructions at higher and higher frequencies with higher throttle settings, without feedback on the rotor's response -- correct? I'm attempting to drink from this firehose, but my capacity is finite.

I appreciate the response, Jay.

-- Reynold

[Q]

I don't think sensors will make a difference. It has everything to do with the amount or torque you need to start swinging a big prop. A low wind does not provide a lot of torque. It does provide a lot of speed though.

So your options are to rewind with more turns or to use a smaller, lighter prop. It all depends on what kind of prop you want to use and thus what kind of flying you want to do.