knocking noise from brushless hub motor

[silversurfer]

Hi, since getting my S/H Torq some of my retired friends have also bought (on ebay) a selection of electric bikes.My garage is becoming a regular repair shop!
A friend has a Thompson Euro Classic (single speed, rear hub motor). The wheel spins smoothly and noise free, but once switched on (no throttle used), when the wheel is turned by hand it knocks, 9 knocks per rev. When motored on the throttle it makes an audible knocking relative to speed. When ridden it still knocks but it is not quite as noticable? perhaps the load/effort absorbs the sound to some degree?
It sounds as if the rotor/stator are catching? My Torq makes a slight growling, like an old tramcar, but this is a definite 'knock'. Should we strip the hub, or let it 'develop' ?
We originally did remove the motor side plates, just to check there were no wiring/bearing problems (before even attempting to run the bike) and it seemed fine.
I understand from other past posts that some motors do make a slight knocking but this is quite loud, perhaps we should reposition the side plates to a different set of holes? Any tips gretefully welcome, thanks, silversurfer.

 

[flecc]

The earlier Euro Classic that I know had a 180 watt brush motor, but that was due to be upgraded to a brushless, though I'm not sure what controller type. If it's a bike that has power from a standstill and doesn't have to be pedalled to 2 or 3 mph to get power, it will have an 8 wire motor to controller connection.

3 wires are heavy power phase ones, and 5 are thinner Hall sensor connections. If one of those 5 is open circuit at any point the result is the sort of knocking you describe, the equivalent of a misfiring engine since the phase activation sequence is upset.
.

 

[silversurfer]

Hi flecc, I think you have identified the fault, amazing! Some background info. The original owner had the bike 'borrowed' by the local kids. They caused the back wheel to 'turn' in dropouts, this dragged/broke the tiny wires.
He apparently tried to solder replacements but his eysight was not good enought and he sold the bike on to my friend. I have carfully replaced the five thin wires to the tiny circuit board inside the hub, colour for colour. But only replicating what he did (if he got it wrong so have I !) I seem to remember one position on the board not having a wire, but five wires were used and the three thick ones were OK.
All wires correctly replaced. We did (poor colour rec.) mix thick green and blue, the wheel ran backwards! Soon fixed!
And, confirming your diagnosis, the motor does run with a slight 'missed beat' and sometimes needs to be turned slightly for it to start running. On the road it pulls OK, other than the noise, but following your diagnosis I think a strip down and a check of a wiring diagram, if I can find one, is needed. Many thanks for your prompt reply, Ted

 

[Tiberius]

Hi Silversurfer,

You have to get the 3 motor power wires and the 3 Hall sensor wires connected up properly. In my experience it is not uncommon for the colours to be mixed up, since the controllers and the motors often come from different manufacturers.

There are therefore 36 combinations. But since the motor and the sensor wires can be rotated together through three settings, there are really only 12 different combinations. If the motor and the sensors are set up without any mechanical phase advance then it reduces to 6 different combinations.

Combinations other than the optimum one will produce effects such as:
Runs backwards (you have found this one)
Runs backwards roughly
Runs forward slowly with a nasty knocking noise (you may have found this one too)
Jerks through a partial turn and stops.

It is an interesting exercise, using group theory in mathematics, to work out a strategy for finding the best combination in the minimum number of tries. But it is quicker to try all 12.

Leave the motor wires alone. Try the 6 different combinations of the sensor wires and note the results.
The swap over 2 of the motor wires and try the 6 different sensor combinations again and note the results.
(Depending on the motor, the second set may give the same results, but in a different order).
That way you will have tested all 12 possibilities and can choose the best one.

Nick

 

[silversurfer]

Hi Nick, first thanks for the puzzle, certainly beats suduco! I am so grateful for you and flecc's tips. Followig flecc's comments I have been able to contact the original owner who, in conversation told me the wires should emerge from the 'offside' of the bike and he, in making the first attempt to repair the wires he removed the rotor??? (apparently nearly lost the tips of his fingers puting it back!)and, had put it back mistakenly with the hollow wire outlet on the 'nearside/brake side, I subsequently connected all the wires up in this form! (not having a manual).
So I must strip the wheel, remove and reverse the rotor or perhaps just reverse the side plates ? to start from scratch with the wires emerging to offside/sprocket side. I'll keep you posted, thanks again guys, Ted

 

[flecc]

I can confirm what Nick says about the colour codes in Chinese products often being wrong, so experimenting as he has indicated is the often the only way to sort it out.
.

 

[jcebike]

there is hall-free motor and controller,it just has 3 wires, very easy! maybe you can try...