Conversion for a Dahon Glide (24" wheel, narrowhub).

[Ashaman42]

Hi all,

I wonder if you could kindly offer some advice?

I'm currently commuting on a Dahon Glide (mainly because I can stick it behind my office door rather than using the bike sheds). My commute is 25-28 miles each way but I generally tend to take the bike on the train into work (the early trains are quieter) and then cycle home avoiding the busier afternoon/evening trains. There are a couple lumps along the way but I wouldn't call it hilly. Brighton to Eastbourne via Lewes for those that know the area. I'd imagine I want enough battery capacity to do at least half again a commute to allow for capacity loss over time and for cold weather as I expect I'll be riding through the winter if I can, does getting something with a nominal range of ~40 miles sound sufficient?

I'll be riding in all weathers too so whatever I get needs to cope with possibly heavy rain.

The problems are that I'm a bit too slow and the Dahon is very sit-up and beg which into a headwind is a bit too much like hard work, luckily the prevailing wind tends to be against me in the morning and with me on the way home but not always.

I was looking around at kits to convert to a front wheel hub, I'd like to keep the current rear wheel as the internal gears are nice and out of the elements. I was originally looking at kits from https://electric-bike-conversions.co.uk when a chance comment somewhere made me have a check - it turns out the Dahon fork isn't 100mm wide. A quick poke with a ruler with the wheel in place puts the dropouts at somewhere between 70 and 80mm. I will whip the wheel out tonight and get a more accurate measurement.

I did then after finding this place have a read around and discovered Woosh Bikes, I see that they do a Brompton kit built around the Cute Q70 hub (https://wooshbikes.co.uk/?hubkits#q70kit) so I have thought of either getting it built into a 24" rim or buying it as is and re-rimming it myself. However I have been told that the motor speed is optimised for the 16" Brompton size and that it won't work well in a 24" wheel and is liable to get damaged. However one shop page for the Q70 hub elsewhere (and can I find it again?!) says the Q70 in either 201RPM or 328RPM is often used for 24" wheels (it had a range of wheel sizes for each RPM and there was an overlap at 24") so I'm thoroughly confused.

I have found found Vekkit kits that do a 74mm 24" wheel version which is quite a neat package (https://vekkit.com/products/folding-ebike-kit) and would mount on the Rixen and Kaul mount I already have fitted on the front end. And the wireless sensor and control are quite neat so we just end up with the one wire from battery pack to motor. However by the time I pick the larger battery etc it adds up to nearly £750 which is a fair chunk more than the Woosh for example at ~£550.

I guess what I'm asking is would the Woosh kit not work re-rimmed and failing that how much of a ready done premium am I paying if I go for a Vekkit? I expect I could do it more cheaply myself but how much more cheaply is the question? For the sake of warranty and a known set of bits that work happily with each other rather than needing troubleshooting and head scratching.

Out of interest I read that the legal UK motor limit is 250W, can a larger motor be used if it's "restricted" or is 250W absolutely the limit? Is there even any benefit to a larger motor if kept to 250W/15mph? If I do go homebrew I'd rather have everything neat and legal as I'll be doing a lot of miles and it's just plain simpler to avoid any potential worries.

Sorry that's all a bit of a wall o' text. I think I've covered the salient points though and any advice would be appreciated. Do ask clarification questions if anything hasn't made sense.

 

[vfr400]

I doubt that you'll find a suitable ready-made kit. You can't use a Brompton one because the motor will be too fast for a 24" wheel. My recommendation would be the Q70 from BMSBattery. I haven't used this motor myself but it looks perfect. The only problem is that the two different versions both have the wrong speed. 328 rpm will be much too fast and 201 rpm would give you a max speed of 14 mph, which you'll probably find too slow, especially when your battery runs down and reduces it to 12 mph.

What I'd do is use that 36v motor at 48v, which will increase the max speed to 18.5 mph, which should give good power at 15 mph. The extra volts won't do the motor any harm. It only changes the maximum speed.

The ideal current at 48v would be around 12 amps. Again, you won't get that in an off the shelf 48v controller, but some controllers have adjustable current via the settings in the LCD.

Considering everything, I'd use that motor with a 48v rack battery of the type that has a compartment for the controller at the front of the receiver, then get the 48v 15 amp sine wave controller with the throttle, speed sensor, LCD3 and PAS from PSWPower.

Q70 36V250W Front Driving V-Brake Hub Motor RPM 328

Q70 36V 250W Front Driving V-brake, rim-brake E-Bike Hub Motor. Waterproof Hall Sensor and Sensorless compatible plug.

bmsbattery.com

36V 48V 250W 15A 6Mosfet Waterproof Sinewave ebike Electric bicycle Brushless Controller fit KunTeng KT Series LED LCD - PSWPOWER.com

www.pswpower.com

Bear in mind that an electric kit will add 5 or 6 kg to your bike, which makes it much more awkward to fold and carry.

 

[Ashaman42]

Hi vfr400,

Thanks for your feedback. I must admit to some confusion. It looks to me like the Woosh kit uses the same Q70 hub, admittedly at the 328rpm which you say will be too fast. But I've been told using the Woosh one in a 24" rim will damage and yet you say to use the same motor from BMS instead.

When you say it'll be too fast do you mean that this is what will damage it? If so would running it at 48V (and therefore faster) not be even more of a problem?

I appreciate your point about the extra weight but it's a heavy lump already so what's a bit more eh? In all seriousness it's a bugger to carry folded and easier unfolded, there's a nice gap in the frame that acts as a handle and lifting there puts the saddle nose nicely on top of my shoulder. Given the weight of the back end with my saddle bag and the hub gear if I put the motor and battery on the front I think it would actually balance better albeit heavier. I mostly wheel it folder anyway and it's really only a single flight of stairs between the station platform and street that need lifting for.

Doing a bit more research the other day I did find some aftermarket Dahon forks that have a 100mm oln but I have only found these for their 20" folders and not the 24". They do do a steel version of my fork that could conceivably be cold set wider but 25mm seems like quite a big stretch, not sure I'd be happy doing that. I did email Dahon asking about forks as I know at least some of their bikes (maybe all) have a internal threaded headtube. Thinking if I was lucky and the Dahon Glide can take a normal fork I could just get whatever 24" fork and yeah I'd lose the magnet (for keeping the folded bike folded) and light mounts but I'm sure I could fabricate something for that. Alas Dahon's response didn't answer anything about the forks just a simple we don't recommend conversion, buy our electric folder if you want a motor.

I did find the Tern Vectron which looks very nice but £3500 is a wee bit out of budget.

I did email Vekkit about their kit and found they use a AKM 74mm motor but again it's 328rpm which they said would work but that I'd lose some torque and get a higher max speed but that this could still be locked down to the UK limit in the control app. They couldn't say exactly how much torque I'd lose. They do have a 21 day trial and pay return shipping if it doesn't suit... It is quite expensive though. I do like the wireless aspect mind - is that something that can be done reasonably simply in a homebrew setup?

I guess this would work, I'm not looking for something to drag me the whole way to work with me gently turning the pedals over, I'm happy to work I just want something to reduce the long slow hill drag loses and the fiddly bits in the more junctiony bits of the journey. I currently manage about 11/12mph overall journey average on the folder vs ~14 on my nicer bike.

I did have a look at a couple middrive kits as well but I think the geometry of the frame around the bottom bracket/fold hinge rules them out.

I will keep researching and looking at my options.

 

[vfr400]

328 rpm will be too inefficient at low speed, so it'll lack power, overheat both your controller and the motor itself at the same time as drain your battery quickly.

Running the Woosh motor in a 24" rim does exactly what I just said above.

You need a 36v 201 rpm version. When run at 48v, it becomes 260 rpm, which is perfect for what you want.

 

[Ashaman42]

Ah I see. Thanks for the clarification.

 

[Ashaman42]

What about coming at this from the other direction? How closely does a middrive fit to the bottom bracket shell? I've attached some photos of the underside of the Dahon.

Obviously I'd have to lose the centre stand but if either a Bafang BBS01B or a Tongsheng TSDZ2 would fit between the protusion of the seat tube and the wee nubbin that sticks up (well - down when the bike is rubber side down) to stop the stand rotating then that might be an approach. I could probably fabricate a new mount for the stand that would go in the base of the seat tube and wrap the legs around the motor.

In some ways I'd prefer the TSDZ2 though it's a little concerning that it's only IP54 rated given this will be an all weather commuter.

Ideally I'd stick a slightly smaller chainring on so I can keep the chain case. But I might be able to make a new chaincase at work with a bit more clearance if needed.

Excuse the skog, I cleaned it Sunday and then Tuesday's commute covered it in grot. If it stops raining today I'l drag it into the garden for half an hour and give it a once over.

 

[vfr400]

From what I can see, I'd say no chance.

 

[Nealh]

BBS01 has about 6mm clearance from the BB shell when fitted TDZS less so.

 

[Ashaman42]

I'll have a measure after I've given it a clean. I'll google tomorrow but I don't suppose you have the "motor cylinder" size to hand do you? No use clearing the shell just to hit either the seat tube or the stand stub.

When you say 6mm do you mean from the outer edge of the bottom bracket shell?

 

[Nealh]

Yes, BB face to BBS outer shell face.
Your issue is you have know where near that, the seat tube and the strengthening plate the extends down in front of the BB makes it impossible for the BBS to slide on.

 

[PaulM24]

As a recent buyer of a very good condition Dahon Glide, I wonder why the use of the alternative 201 rpm Q70 motor in a 24 inch wheel was not considered further, as it would be a relatively simple change to the Woosh Brompton Q70 kit, with just a different wheel and the controller set up for a 24 inch rather than 16 inch wheel diameter.

I accept that it may run slightly slower than the 15.5 mph limit; using 2 pi r to calculate the rolling radius, the Brompton 16 inch wheel with 328 rpm motor gives 5248 pi and a Dahon Glide 24 inch wheel with 201 rpm motor gives 4824 pi. Assuming the Brompton runs assisted up to 15.5 mph, this would give a assisted cut-off of 14.3 mph for the Glide. Furthermore the 24 inch wheel probably uses chunkier tyres than the Brompton as well (mine has Schwalbe Big Apple tyres), which would help the relative gearing too.

For me the main use of electric assist is primarily for hill climbing, a slightly lower speed would still enable me to maintain a satisfactory average speed.

 

[guerney]

Would these be any good?

Lekkie BB86/92 Bafang Adapter

Bafang BBS01B BBS02B bottom bracket adapter for PF86/92 BB86/92 bottom brackets.

www.brightonebikes.co.uk

Lekkie PF30 Bafang adapter

Electric bike conversions in Brighton and Hove. Bespoke E-bikes with Bafang BBS01B BBS02B BBSHD motors and quality lithium-ion battery cells. E-bike fitting service. Lekkie Bling Ring stockist

www.brightonebikes.co.uk

 

[Woosh]

As a recent buyer of a very good condition Dahon Glide, I wonder why the use of the alternative 201 rpm Q70 motor in a 24 inch wheel was not considered further, as it would be a relatively simple change to the Woosh Brompton Q70 kit, with just a different wheel and the controller set up for a 24 inch rather than 16 inch wheel diameter.

I accept that it may run slightly slower than the 15.5 mph limit; using 2 pi r to calculate the rolling radius, the Brompton 16 inch wheel with 328 rpm motor gives 5248 pi and a Dahon Glide 24 inch wheel with 201 rpm motor gives 4824 pi. Assuming the Brompton runs assisted up to 15.5 mph, this would give a assisted cut-off of 14.3 mph for the Glide. Furthermore the 24 inch wheel probably uses chunkier tyres than the Brompton as well (mine has Schwalbe Big Apple tyres), which would help the relative gearing too.

For me the main use of electric assist is primarily for hill climbing, a slightly lower speed would still enable me to maintain a satisfactory average speed.

the Q70 on the Brompton kit is a front motor optimised for the Brompton wheel whose circumference is 1.3M. your Dahon P8 Glide has 47-507 tyres, 1.89M circumference, it will be outside its optimal setting, you'll keep the speed but lose a fair bit (30%) of torque, maximum torque is 40NM * 1.3/1.87 = 27NM.


the torque

 

[PaulM24]

Thanks for the replies, a question for Woosh; your Brompton kit has the Q70 motor running at 328 rpm, what would happen if the 201 rpm Q70 motor was used instead. From your explanation, using the Q70 201 rpm motor, would I keep the speed but loose some of the torque and hence get less hill climbing performance? The question would be is 27NM enough?

Thanks also for the information on the Bafang adapter, this is going beyond what I am considering, however it hopefully will be useful information for other forum members.

 

[Woosh]

Thanks for the replies, a question for Woosh; your Brompton kit has the Q70 motor running at 328 rpm, what would happen if the 201 rpm Q70 motor was used instead. From your explanation, using the Q70 201 rpm motor, would I keep the speed but loose some of the torque and hence get less hill climbing performance? The question would be is 27NM enough?

if you have the 328rpm Q70, you keep the speed (you can run the bike up to 37kph on a flat road when derestricted, 1.89M * 328 * 60/1000) but the climbing torque is poor.
If you have the 201rpm motor, top assist speed is 22.7kph and climbing torque is much, much better, up to 40NM. A better option.