Hub motor suddenly starts thump-thump-thimp

[twinotter]

I have a G320.250.R front hub motor with a KT36 / 15A controller on a Yuba Mundo V4.3. Total weight about 400lbs with me, bike, & pax. While riding today with the two daughters, suddenly the motor started going thump-thump-thump as the wheel revolved.

I noticed the front wheel doesn’t rotate easily backward (but don’t remember if that was always the case). It still freely rotates forward. Without power, there is no grinding or thumping, and it doesn’t have obviously more resistance to turning - it free spins and slows down at about the rate I would expect.

With the front wheel lifted up, it rotates under power easily but still thumps. While driving, it feels like it generates less power.

I have a EggRider and its current display seems to spike rapidly but intermittently to about 13A.. I believe previously it fluctuated but was always about 7A.

I can’t audibly tell whether the thumping is coming from the motor or the controller because the controller is mounted on the front fork arm.

This has been working fine for about 300 miles / a year of service on short trips. This was another short trip when it started doing it.

How can I tell if it’s the controller not actuating a phase correctly or if it’s something inside the motor and a mechanical problem. It was one of the ebay’d $50 motors, so I’m not that upset, but I’d like to know the problem before either replacing the motor or upgrading the motor.

Thank you!!
Rudy

 

[neptronix]

Geared motors are sensitive to forces/weight and the gears ( usually plastic ) tend to break in them as a result. 400lbs sounds like trouble for a geared motor, but not a DD.

If you have a throttle, you can put the front wheel in the air and see if you can hear the thump. Maybe flip the bike upside down and listen to which component is making the noise.

My money's on - you're missing a few teeth in your geared motor from the high wear.

 

[twinotter]

I opened the case to look at the gears… i couldn’t easily turn the planetary set, but I did see at least one chip on a nylon gear. That, plus the fact the tire no longer freely turns backward makes me think you’re right, though I don’t quite understand the mechanism of that…

I found this kit on Aliexpress: https://www.aliexpress.us/item/3256803070037306.html?gatewayAdapt=glo2usa4itemAdapt

Will I regret going down the path of fixing these and getting back on the bike as usual? It worked well for a year and a half…

Btw, when I put it back together, it seems the planetary wasn’t engaging the main gear… perhaps a shim I missed? Anyone know if there’s a specific process for reassembly?

Thank you!
Rudy

 

[neptronix]

I don't see this knick.
Once gears start to go, things get worse quickly.

TBH, this motor is a dual reduction type and these are even less durable than the typical geared motor and you've got heavy weight.
You could replace this but you will need to do this often.

Unsure about the replacement procedure, even if you put things together correctly you could have unsettled the gears in the process.

 

[neptronix]

If there are any gear fragments hanging around, that needs to be removed asap.. and could possibly be blocking the gears.

 

[twinotter]

I was sorta thinking about upgrading my setup. Do you have any suggestions for a better setup? This project was done on the cheap because I was always one of those “ew! Electric??” people. But a hundred pounds of kids and a hundred pounds of bike makes it very easy to drink the kool-aid.

This setup taps out at 17mph. With the girls, I used the eggrider to limit myself to 15, for safety. And it’s fine.. but then there’s that kool-aid. Ideally I’d top out at 22ish in non-kid-mode.

Suggestions for a setup that will meet that? I do like the simplicity of the hub motor. 10 minutes and the bike is back to analog-mode, so it’s not down while I do these repairs. Hard to beat that.

 

[99t4]

DD hub might work. Tell us about any hills on your usual routes. Severity and distance. Also, what size tires?

 

[neptronix]

For this power range, if you don't have major hills to deal with, a Shengyi SX2 from ebikes.ca would be a nice replacement, only a hair heavier and only has one set of gears, very efficient too.

But the total loaded weight of the bike is worrying and i wonder if a any geared motor outside of a GMAC would be able to handle the weight with grace.

Pretty much any 500-1000W rated DD would work, you don't have intense speed requirements!

 

[twinotter]

This is a moderately flat area, but there are some hills. The 250W setup I have drops down to about 10mph on hills.

26” x 2” tires. (700s)

Would using the torque limit with eggrider (just lowering power output) help with heavier loads? Less acceleration means less wear and tear?

 

[neptronix]

How long are these hills? are we talkin' about anything that would tire you out on a regular bike ( sans kids? )

Heat may be a contributing cause of death to the gears due to the high weight, if hills are prolonged.

I think the weight is the bigger problem. On a yuba, more of your rider weight sits on the front fork vs a regular bike, then you've got even more weight on top of that, so that geared motor is taking a real beating from bumps etc

If you want reliable, i think a small DD on the front is in order.

 

[twinotter]

Medium hills. Just enough to leave you tired but not debilitated… when you’re NOT carrying the extra 200#. Actually, with granny gear, no real problem at all.

Thank you for your help. I’m looking at motors from ebikes.ca now…