Xiongda Motor?

[Slopes]

Hi everyone - a newbie here.

I used to cycle quite a bit but not so much these days due to slightly gamy knee and having my (somewhat neglected) bike nicked a couple of years ago.

I've spent the last two weeks totally immersing myself in the possibilities of ebikes and would like to make one. After reading about (but not necessarily understanding) all the various options, I've arrived at an ideal set-up I would most like to build. I wonder if anyone can comment on whether or not it is doable/sensible/legal?

My planned build is:
1) Old DH mountain bike (24" wheels)
2) Xiongda 36V/250w 2-speed hub (front mounted) + 36V lithium battery
3) 3-speed internal hub to back wheel (I don't want derailleur gears)

My intended use is zipping round town (with its various hills) and the occasional (very mild) off-roading. In either situation, it'd be great to feel a bit of extra 'oomph' and that it was fun to ride.

From the various threads I've read, I understand that Xiongda are quite happy to adapt a motor and mark it with the above specifications... and that would certainly be considered if it provided a reasonable amount of power to make the investment seem worthwhile... but I don't know enough to confidently give them a specification for this.

Advice from experienced ebikers - and Xiongda users - would be very much appreciated...

 

[willywombat]

DH bike with 24" wheels ..sounds unusual.

"From the various threads I've read, I understand that Xiongda are quite happy to adapt a motor and mark it with the above specifications... and that would certainly be considered if it provided a reasonable amount of power to make the investment seem worthwhile... but I don't know enough to confidently give them a specification for this."

Not sure what you mean.

 

[danielrlee]

Nothing wrong with 24" wheels and a hub motor will thank you for them over bigger ones.

Geared hub motors certainly have their limits though when it comes to off roading. Jumps (even regular curb hopping) are definitely out of the question, so be sure that you really do mean 'light' before going down that route.

EDIT: I've just noticed your intention to run a front motor with a suspension fork. Forget that. You want the motor in the rear in that case. If you want hub gears on an off road frame (strange combo BTW), get a mid drive motor.

 

[Deleted member 4366]

If your idea is that 24" wheels give more torque, you don't need them with a Xiongda because it gives massive torque in low gear. The low gear is like a winch, which can winch a 100kg rider up a 30% incline with very little pedalling using a bike with 26" wheels.

You should explain a bit more what you want from your electric bike rather than how you're going to do it, then we can give more relevant advice.

There's a few things to think about considering your plan:

1. The Xiongda is quite a wide motor, so you can't have a disc brake if you put one in suspension forks. Normal rim brakes are not the best when you consider the extra weight and speed of an electric bike.

2. The torque from the Xiongda in low gear is exceptional. You'll get skipping and spinning on all very steep hills and on steep hills without a good surface because there won't be sufficient weight on the wheel to get grip. When going uphill, weight is transferred to the back wheel.

3. The 48v version is better than the 36v one. It gives more power, but is otherwise the same. You can turn the power down on the LCD when you don't need it.

4. You should say what you don't like about derailleur gears. Many aversions are based on ignorance. They don't have any disadvantage for normal cyclists using a hub-motor, especially a Xiongda.

 

[Slopes]

Thanks for the replies - much appreciated. Some more info...

I’ve always liked the simplicity, input requirements and overall appearance of a three gear internal hub. On my previous 3-speeders, I spent most of my time cycling around town in the high gear - shifting down only for hills where I couldn't build up enough momentum to get me to the top.

I now have a Proflex K2 frame to convert - which takes a 24" wheel. This has a carbon swingarm at the back, so weight may possibly be an issue with a rear mounted Xiongda - although it seems to be a relatively light motor. This would be my preferred position (the battery will go into the frame triangle, either way).

I read through the long Endless Sphere thread on this motor yesterday and a guy there enquired about building a single-speeder with a rear mounted Xiongda hub. This is closest to what I’m looking for - but I’d like the option of an extra gear to use. Would it be possible to have a single-speed, rear hub arrangement like his but with a 'Metropolis 2-Speed PT crankset' … effectively providing four gears?

I was intending to play safe with a 36v set up, but may go to 48v if it’s noticeably more torquey (I got the impression from the ES thread that there wasn’t that much of a difference).

The bike will mostly be used on the road - with very occasion trips along easy dirt footpaths/fields, etc.

 

[top drive]

Pro flex K2 wasnt designed as a 24" wheel bike .

Thats going to have a somewhat low BB and pedal strikes may become an issue.

Its also worth noting that i would be very careful fitting a rear mounted motor to the carbon rear ended proflex .... they cracked for fun under normal use when they were new - nearly 20 years ago !

 

[Slopes]

Pro flex K2 wasnt designed as a 24" wheel bike .

Thats going to have a somewhat low BB and pedal strikes may become an issue.

Its also worth noting that i would be very careful fitting a rear mounted motor to the carbon rear ended proflex .... they cracked for fun under normal use when they were new - nearly 20 years ago !

26" - you are right (I only have the frame so far, which looks more or less as-new). I'll stay with the wheel size originally intended for this bike. The carbon rear end was one reason (along with internal gearing) for considering a front mounted Xiongda. Although I weigh around 168lb so I don't think a rear mounted hub would place any extra stress on the arms under normal road use.

 

[Slopes]

OK - on further research, this bike did come with 26” wheels. But I think I’ll stick with my original plan to place 24 inchers on my frame. To keep the BB away from the floor, I’ll extend the length of the front forks - thereby raising the front end and tilting the frame back a little.

I am concerned about the carbon fibre back end with a rear mounted hub. But I’ve found a couple of e-bike frames using this material for swingarms on back mounted hubs… so it's certainly doable. My worry here is more with torque and slippage on the axle - and where to place a torque arm (if needed) without it overly stressing the CF.

 

[danielrlee]

I'm not sure the CF swingarm is suitable. The thicker motor axle will require that the dropouts be made deeper and I'm not sure that this will be do-able.

EDIT: I've just had a closer look and it appears your dropouts might me made from a different material. Is this the case? If so, what are they made from?

 

[anotherkiwi]

That looks awfully like an aluminum insert into a CF tube.

 

[D8ve]

With electric 3 speed hub will do but the normal! First choice hub is the 8 speed shimano. As nexus its a fair price and will give you get home ratios with a flat battery. The Alfine is considered bomb proof and great for me. Circa £200 inc wheel with disk brake. You may get cheaper..

 

[danielrlee]

That looks awfully like an aluminum insert into a CF tube.

I think you're right.

The more I think about it, the less I think this frame is suited to a rear hub conversion. What it's crying out for is a mid-drive.

 

[top drive]

its not so much the material as the manufacturing processes that have changed in the last 20 years.

Id take any modern(non race) carbon frame and have no qualms fitting a rear hub motor to it ....

Those proflex werent even good at staying in one piece under human power !

 

[trex]

I would forget the XD motor and fit a BBS02 to this bike.

 

[KirstinS]

I would forget the XD motor and fit a BBS02 to this bike.

And forget the 24 inch wheels as the bbsxx will get smashed to bits

 

[Slimjim]

As a mountain biking mech engineer, I'd certainly be wary of fitting a rear motor hub to that frame. The bike has V-brakes therefore the dropouts on the rear swingarm were never intended/designed to withstand torque loads. Obviously a torque arm could help, but then if you're not careful, you would be placing a spot load onto the swing arm - and clamping around carbon fibre with a metal clamp would potentially put a 'sharp edge load' against the carbon's surface. Might lead to cracking when combined with the actual suspension loads and twisting of the arm. At the very least i would suggest bonding a reasonably large alu plate to the carbon, then clamping a swing arm against this. But even then I personally wouldn't risk it. Mid drive sounds the best compromise, then you can use the bike off road.

 

[Slopes]

Thanks, Slimjim - very useful advice. I was actually thinking of wetting on a couple more layers of CF to the swingarm to give it more strength. If this is possible, I could - at the same time - bond on an alu plate for the torque arm... as well as add whatever is required to fit a disc brake. As there will be no cassette, I think I'll have plenty of room for these additions. Do you think this would work?

 

[Slimjim]

Thanks, Slimjim - very useful advice. I was actually thinking of wetting on a couple more layers of CF to the swingarm to give it more strength. If this is possible, I could - at the same time - bond on an alu plate for the torque arm... as well as add whatever is required to fit a disc brake. As there will be no cassette, I think I'll have plenty of room for these additions. Do you think this would work?

Possibly but as with any modifications to a structural component, if you make it significantly stiffer in one area, the stress around the edge of the reinforced zone increases, as the un-reinforced regions try to flex. I've only got limited experience with CF, I would taper-out the extra layers to gradually reduce their stiffness towards the edges. This helps to avoid 'stress risers/raisers'. And avoid running any new edges across the fibres, or directly along them. 45degrees would seem sensible.

But I think a few more experienced CF-frame owners on here might point to the various photos in the web of what happens to a carbon frame it it cracks or suddenly fails.....

And whilst you can do a fairly simple calculation of the load that the torque arm would apply at full motor torque, based on its length, there is always the risk of impact torque loads that would be significantly higher than peak motor torque.

The main issue may well be the age of the carbon swingarm, as others have highlighted, and fit example whether there are any underlying cracks or she defects.

Don't forget, if the hub motor is heavy, then when the swingarm bounces back say over a jump, the extra mass will have to be absorbed at the drop outs, and at the shock linkage as the shock suddenly reaches full extension. If you can adjust/reduce the rebound speed of the rear shock, you could reduce the increase in impact load.

I'm just guessing at all of the above btw, I don't have enough specific experience for you to base any decisions on my ramblings! It's a nice, classic frame, be a shame to damage it.

 

[Slimjim]

Oh, and if you only reinforce one arm of the swingarm, I'm guessing that the swingarm will tend to twist under load, add the un-reinforced arm will bend more.

 

[Slopes]

Again, great advice, thanks. I would, of course, reinforce both arms, equally, to balance things up. Another thought I've had is to get the swingarm remade in alu... maybe CNCed from (say) flat 12mm plate to the contours of the existing item and then welded. The frame is currently on the way to me from the U.S... so I've nothing but photos and technical drawings to look at.