I wanted to provide an update on the reliability of the Derby Cycle Impulse II motor system. I own a bike shop in Boulder, CO and used to focus exclusively on electric bikes. I've sold thousands of electric bikes and serviced many of the bikes on the market current and past. I'm a Mechanical Engineer by training, have worked in Silicon Valley as an Electrical Engineer, and a certified machinist so I have quite a bit of background with motors from both a mechanical and electrical standpoint. I have a few customers that purchased the Focus Thron Speed 27.5 bikes equipped with the Impulse II motor system. One of those customers recently experienced a loud noise which he thought was coming from the motor. Upon inspection I could tell immediately that it was a bearing. Since Focus USA decided not to warranty the problem, I decided to open the motor and fix it myself. What I found was interesting. Bearing failure was indeed the issues but I found that the bearings used on the part of the motor that failed were, in my opinion, severely undersized. Most of the e-bikes that I have sold have been equipped with the Panasonic mid-drive. I have customers that put 8-10 thousand miles a year on those bikes and they never fail. Personally I ride a bike with a Panasonic motor and I have just over 39,000 miles on the bike (not a misprint). The offending bearing on the Impulse motor is located on the gear reduction shaft, which holds the large plastic/nylon gear with the one way bearing. I am posting a picture of the bearing sitting next to the same bearing from the Panasonic motor. As you will see, the Panasonic is MUCH bigger. This customer with the Focus Thron has just over 2500 miles on the bike. In my opinion, that is still low mileage. For a bearing to fail after so few miles is shocking.
Reliability of Impulse Motor
- Thread starter Frefol
- Start date
probably lucky they didnt jujst use a bushing
PaulD
1 kW
Thanks for posting. Good info on the reliability of the Panasonic drive.
That bearing does look a little undersize, can you read the size on it and the Panasonic bearing? If you have pictures of the inside of the impluse motor/gear reduction, that would be helpful... should be able to ballpark the bearing loads knowing gear sizes and torque.
That bearing does look a little undersize, can you read the size on it and the Panasonic bearing? If you have pictures of the inside of the impluse motor/gear reduction, that would be helpful... should be able to ballpark the bearing loads knowing gear sizes and torque.
PaulD
1 kW
Thanks for the pics. Here are my ballpark calcs:
They are claiming 80Nm of torque, and thats about a 6:1 secondary reduction. So, thats about 1000N of force assuming that steel gear is about 80mm pitch diameter. Since the motor, secondary axle and BB axle are all in a straight line, the radial force from the primary reduction gets added to this 1000N to make about 1222N. It looks like the narrow width 6801 bearing is sandwiched between the two gears, and therefore takes the majority of the load ( I didn't do a force balance, but this is worst case)
I used the bearing life calculator here: http://www.engineersedge.com/calculators/ball_bearings_life_calculation-1.htm
Using the 430lb dynamic load rating for that bearing, operating speed of 300 rpm (50rpm at the crank), a few other variables considering shock load (shifting gears on a mid drive), and it spits out sub 100hrs of bearing life... keep in mind this is all at peak torque, but we can assume a mid-drive spends a decent portion of its time at peak torque.
So 100hrs, assuming a 15mph average speed would be 1500 miles... I said it was ballpark
Having said all of that, I would never have spec'd a 5mm wide bearing in that location even before any calcs. Somebody check my math!
They are claiming 80Nm of torque, and thats about a 6:1 secondary reduction. So, thats about 1000N of force assuming that steel gear is about 80mm pitch diameter. Since the motor, secondary axle and BB axle are all in a straight line, the radial force from the primary reduction gets added to this 1000N to make about 1222N. It looks like the narrow width 6801 bearing is sandwiched between the two gears, and therefore takes the majority of the load ( I didn't do a force balance, but this is worst case)
I used the bearing life calculator here: http://www.engineersedge.com/calculators/ball_bearings_life_calculation-1.htm
Using the 430lb dynamic load rating for that bearing, operating speed of 300 rpm (50rpm at the crank), a few other variables considering shock load (shifting gears on a mid drive), and it spits out sub 100hrs of bearing life... keep in mind this is all at peak torque, but we can assume a mid-drive spends a decent portion of its time at peak torque.
So 100hrs, assuming a 15mph average speed would be 1500 miles... I said it was ballpark
Having said all of that, I would never have spec'd a 5mm wide bearing in that location even before any calcs. Somebody check my math!
natted
1 µW
Were you able to repair the motor successfully? Aside from the bearing, do you think any other parts of the motor are not fit for purpose?
Right now I have to decide on a new bike with either Impulse 2 or a Bosch motor. The bike I wanted has the Impulse 2 but if it isn't a reliable system then I may need to choose something else.
I don't particularly want to have a giant paperweight after the 2 year warranty period ends.
Right now I have to decide on a new bike with either Impulse 2 or a Bosch motor. The bike I wanted has the Impulse 2 but if it isn't a reliable system then I may need to choose something else.
I don't particularly want to have a giant paperweight after the 2 year warranty period ends.
I just replaced an Impulse motor. You can get an exchange (new) one from Germany for about £360 plus shipping costs each way. It comes with a 2 year guarantee and swapping the motors is dead easy. Obviously, it would be cheaper to just change the bearing, but there's probably consequential damage to other components to consider.thechod said:
http://www.pro-cycling-golla.de/Motor_und_Zubehoer/Motor_Tausch_ausserhalb_der_Garantie_und_Gewaehrleistung_artikel580515b352f96.html
PaulD said:Thanks for the pics. Here are my ballpark calcs:
They are claiming 80Nm of torque, and thats about a 6:1 secondary reduction. So, thats about 1000N of force assuming that steel gear is about 80mm pitch diameter. Since the motor, secondary axle and BB axle are all in a straight line, the radial force from the primary reduction gets added to this 1000N to make about 1222N. It looks like the narrow width 6801 bearing is sandwiched between the two gears, and therefore takes the majority of the load ( I didn't do a force balance, but this is worst case)
I used the bearing life calculator here: http://www.engineersedge.com/calculators/ball_bearings_life_calculation-1.htm
Using the 430lb dynamic load rating for that bearing, operating speed of 300 rpm (50rpm at the crank), a few other variables considering shock load (shifting gears on a mid drive), and it spits out sub 100hrs of bearing life... keep in mind this is all at peak torque, but we can assume a mid-drive spends a decent portion of its time at peak torque.
So 100hrs, assuming a 15mph average speed would be 1500 miles... I said it was ballpark
Having said all of that, I would never have spec'd a 5mm wide bearing in that location even before any calcs. Somebody check my math!
seems about right...mine is now 2016 miles and clacking and obviously had its day...but it was failing way before that ...
Thanks for this post. It seems very helpful.Has my impulse 2 motor died on me 2 days ago. Seems too work but wen i put too much presure on peddles i get funny noises coming from the motor. Will open the motor up when I get the tools. Not sure if I need special tool for the flywheel/crank/peddle removel ?.bike is focus jarifa 27s. after reading these post. Don't think I will waste my money on new motor for it to happen again. Maybe I could try putting hub motor on too convert it .Shame as everything on the bike is spotless and in good condition .bike has only done 1500 miles. Well at least still got good parts hopefully fit on my next ebike.
Supercadet
1 µW
- Joined
- Sep 7, 2018
- Messages
- 1
Hi regarding your post on Impulse 1 1 motors which I found most interesting by the way could you tell if it caused much damage getting bearings out and did it require any special tools. It's that I have 2 Impulse motors and would like to change bearings before rather than wait for other damage to occur. Thank you again
knutselmaaster
1 kW
Impulse motors are terribly unreliable, as stated above they have a huge design flaw. Replacing the bearings is quite easy and doable without expensive special tools but the new bearings will break down too. Preventive replacement will make it last longer but you will have to do it really often, like every 1000 miles...
markz
100 TW
noratrace said:
Did you see with your own eyes the damage?
Yes did see the damage. The white round cheap plastic thing inside had no teeth or cogs left in a lot of places .I looked for parts online b ut couldn't see enything. I brought the bike second hand for a 1000 pound.(maybe he knew it was about to pack up hence so cheap ) I coulda brought new motor for it. But if it had too go to be reprogrammed for the new motor etc. The bike shop may of said that this bike is pinched (not that i know if it was )I didn't want to waste more money and time for the motor to go bad again .So I brought brand new ebike from a shop.and plus it may of taken ages for bike to be mended. Thanks for reading .got rid of motor and frame now so no fixing available lol but kept everything else from the bike. Just wondering could I use the display on another ebike? Or is it waste time keeping it?
knutselmaaster
1 kW
Yes, that is what always happens. The bearings get "loose" and as a consequence the big white cog gets to suffer, making it break all tooth.
The weird thing is that they made several revisions of the motor but they never seemed to implement a durable solution.
It seems so simple, just take bigger and stronger bearings and a more solid housing around them...
The weird thing is that they made several revisions of the motor but they never seemed to implement a durable solution.
It seems so simple, just take bigger and stronger bearings and a more solid housing around them...
miro13car
100 kW
does it make sense to replace motor which has bad design?
bearing is too small to handle the load.
bearing is too small to handle the load.
After reading this article about how crappie motors was. that was another reason I didn't replace motor .as I didn't want it to happen again.and wasting more money .bike was nice and you could choose ur speed up to 28mph on the display . pity my new ebike hasn't got that facility/feature
It seems that's the inevitable fate of all Impulse motors. Mine Evo one doesn't have stripped cogs yet. The paws seem worn a bit. The bike is still working but cutting off. I suppose due to faulty cadance sensor. I left it to my gf as she puts a lot less torque to its cranks(55kg) and it behaves with her.
I also got myself a new Giant(yamaha) ebike from the shop after my experience with that crappy Impulse stuff.
I also got myself a new Giant(yamaha) ebike from the shop after my experience with that crappy Impulse stuff.
Hello,
I am having problems with the torque sensor of this motor: It seems jammed a bit, when I push too much on the pedal sometimes the motor remains engaged also when I release pressure for sometime. Does anyone have had that or have a clue of how to fix that.Is it even possible to find that torque sensor as a spare part and replace it or do I need to change the whole engine? I was at this point if I can't replace it sostitute it with a cheap cadence sensor.
Any input from the community would be highly welcome.
Thanks
Alberto
I am having problems with the torque sensor of this motor: It seems jammed a bit, when I push too much on the pedal sometimes the motor remains engaged also when I release pressure for sometime. Does anyone have had that or have a clue of how to fix that.Is it even possible to find that torque sensor as a spare part and replace it or do I need to change the whole engine? I was at this point if I can't replace it sostitute it with a cheap cadence sensor.
Any input from the community would be highly welcome.
Thanks
Alberto
