Lightweight folder - build thread

[Jeremy Harris]

One of the joys of having milling machines in the workshop!

The cut outs for the DB25s could be cut by hand, if you decided to use three bits of plastic rather than two. The middle bit would have a slot that was a clearance fit for the whole connector, with the outer bits having slots just big enough for the back of each one. I drilled and tapped holes in the Delrin for the screws, but you could just as easily fit longer screws with nuts on the back. The blocks were clamped together and drilled/milled as a pair, to ensure perfect alignment. The holes for the high current pins were drilled undersize and then reamed to a very tight push fit. I'm planning on adding some adhesive on the back to make doubly sure that these connectors stay in place.

 

[cwah]

Thanks jeremy. Good idea about slicing the plastic in 2 part to fit the db25. I'm now thinking about using the remaining polycarbonate sheet I have from my battery box, a db25 and potentially use a complete HTX 4 mm bullet connector with the plastic cover. As this cover helps the connector to fit in the hole. It could be quite practical to keep that.

 

[Jeremy Harris]

Another way of making a high current multipole connector that I looked at was to glue some Dean's Ultra connectors together. These stack side by side, in alternate pairs, to form as big a connector as you need. The only downside to using lots of Deans plugs/sockets is the relatively high mating/de-mating force needed. This may or may not be a significant problem.

 

[nieles]

these connectors would be a really elegant solution for the power connectors. not cheap though

they are available in 2 types of male plug and one type female

 

[Kin]

I'm a fan of http://www.citizenbike.com, and have the http://www.citizenbike.com/catalog.asp?product_category_id=1&product_id=24. It's a bit too beefy to some extent on the alluminum, so it could be a bit lighter. Also, the standard gearing is set too low at top speed . (probably ~18mph, I've not checked or bothered calculating, but not >20mph)


I think you may have actually already chosen your folder, but I look forward to seeing how this goes.

 

[Jeremy Harris]

these connectors would be a really elegant solution for the power connectors. not cheap though

they are available in 2 types of male plug and one type female

Nice find! They seem to be a fair bit cheaper at Mouser: http://uk.mouser.com/search/refine.aspx?Ntk=P_MarCom&Ntt=140528472 although those prices probably still get hit with import charges, VAT etc. Good for 55 A per pin, apparently (http://www.amphenolcanada.com/ProductSearch/pdf/LCC17_BRO.pdf) and there seem to be some other nice connectors in this range: http://www.amphenolcanada.com/ProductSearch/pdf/COOLPOWER_CAT.pdf.

I'm a fan of http://www.citizenbike.com, and have the http://www.citizenbike.com/catalog.asp?product_category_id=1&product_id=24. It's a bit too beefy to some extent on the alluminum, so it could be a bit lighter. Also, the standard gearing is set too low at top speed . (probably ~18mph, I've not checked or bothered calculating, but not >20mph)


I think you may have actually already chosen your folder, but I look forward to seeing how this goes.

I like the style of that Citizen bike, but you're right, it's a bit on the heavy side. I've got a Swift on order now, just a frameset and some other parts so I can add my own wheels, BB etc. Gearing is a problem on most folders, it seems, few seem to have big enough chainrings, or small enough sprockets, to be able to realistically pedal at anything over 15 to 20 mph. It's one reason I've bought a Speed Drive, as this means I can fit a 48T chainring and it will act as though it's a 79T chainring when the speed drive is engaged. Coupled with a single speed 14T freewheel this will give me a cadence of just under 75 at 25 mph, which seems OK, as I don't like spinning much. With the Speed Drive disengaged the cadence will be about 74 at 15 mph, so OK for low speed riding. The big gap won't matter much as I can just use the motor, I find I stay in top gear (a 50T/12T combination) all the time on my present 20" wheel bike but even that ratio means pedalling uncomfortably fast at max speed (cadence is around 97 at 24 mph, a bit too fast for me).

 

[Alan B]

Which freewheel are you planning to use?

 

[Jeremy Harris]

Which freewheel are you planning to use?

Current plan is to just remove all the other sprockets from a 14-28, as the smallest single speed I can find that will fit a standard freewheel thread is 16T. I could use a 16T and then fit a bigger chainring, but there are potential problems with chainrings over about 50T on some folders (not sure about the Swift though), plus finding a big chainring with a 110mm PCD fixing seems to be harder than I thought it might be.

 

[Alan B]

The high speed drive would come in handy here, aside from the cost.

 

[Jeremy Harris]

The high speed drive would come in handy here, aside from the cost.

Yes, it's the reason I decided to splash out and get it. I've just found a reasonably priced 52T 110mm PCD chainring, so I may be able to go for a 52T/16T set up, with the Speed Drive effectively making the 52T almost equivalent to an 86T. It depends on whether the combination of the Speed Drive and 52T chainring is OK on the frame, something I can't check until it gets here (maybe next week if I'm lucky with the shipping from the US).

 

[Miles]

Jeremy,

I've got a spare 15t freewheel if that would help?

 

[Jeremy Harris]

Might well do Miles, thanks, I'll get in touch once I have the frame and know whether or not I can fit a big chainring OK.

Out of interest, where did you find a 15T freewheel? I've been searching high and low and the smallest I've found that fit a standard thread seem to be 16T, the next size down seems to be the smaller thread fitting BMX 14T ones.

 

[Miles]

AC Racing made one. I bought a couple of them a few years ago, from Harris Cyclery. No longer available, AFAIK.

 

[Jeremy Harris]

That's a very nice looking freewheel, pity they stopped making them.

 

[Alan B]

The speed drive is 1.65x, the high speed drive is 2.5x but apparently no low cost clone is available for the high speed drive.

The 15T freewheels reportedly had reliability issues.

On some motors the freewheel thread piece is removable, if there is enough room to make a smaller thread BMX size unit then the smaller BMX freewheels would fit. Those go down to 14T or so.

Also, I've seen at least one hubmotor with spline for the cogset, that would open up a lot of options.

 

[Jeremy Harris]

The speed drive is 1.65x, the high speed drive is 2.5x but apparently no low cost clone is available for the high speed drive.

The 15T freewheels reportedly had reliability issues.

On some motors the freewheel thread piece is removable, if there is enough room to make a smaller thread BMX size unit then the smaller BMX freewheels would fit. Those go down to 14T or so.

Also, I've seen at least one hubmotor with spline for the cogset, that would open up a lot of options.

Yes, I already have an ATS Speed Drive, Alan, bought it from Accountant specially for this bike, to ease the problem of being able to pedal at speed with these small wheels. The High Speed Drive would have been nice, but the price was just too high for me to justify.

Good idea about machining up a new freewheel adapter for the motor. If the BPM casing is like that one one or two others then I could indeed make up an M30 threaded adapter and then fit a BMX freewheel. The newer Bafang CST has a spline, but its an expensive motor and doesn't (AFAICS) come in the fast wind that is available on the BPM, although it's near-impossible to tell, as Bafang and all the various vendors seem to have conflicting information when it comes to motor Kv.

 

[Kin]

Ah, these speed drives look super cool. I'll keep my eye out in the long term to maybe find one. I've seen internal hub gears to replace cassettes, but this is the first time I actually understood what that crankset replacement does.

 

[Alan B]

I understand about the cost of the high speed drive. Still, might have to get one.

What adhesive do you use on Delrin?

 

[Jeremy Harris]

What adhesive do you use on Delrin?

Strictly speaking it won't be working as an adhesive, as the surface energy of acetal is too low without special treatment to get a decent bond. The plan is to just apply some thickened epoxy to the rear, mechanically keyed using small angled holes. I doubt the connectors could push out, as I had to use a press to get them in, but acetal does have a fairly high coefficient of thermal expansion, so they could possibly loosen if the blocks get warm.

 

[Jeremy Harris]

More bits have arrived. I've settled on a 50T chainring (a Stronglight alloy one) and a standard 16T Shimano freewheel, at least for now. I couldn't run to an ENO, just too expensive for my taste, good as it might be.

With the Speed Drive this will give me 63 gear inches in direct drive an 103 gear inches in speed drive, which seems reasonable. The cadence for 15 mph in direct drive or 25 mph in speed drive will be about 80, which seems reasonable as that's about as fast as I'm comfortable with. It looks like cycle path riding will be in direct drive and higher speed road stuff will be in speed drive, so I'll be pedalling a little faster than at present on the cycle paths, but I'll now be able to pedal up to traffic speeds on the roads, which is probably as good a compromise as I'm likely to get. A bit taller gearing would be nice, but it's hard to fit anything bigger than 50T to this bike, and to go smaller than 16T it looks like I might need to make up an M30 freewheel adapter, or perhaps modify a multi-speed block by machining off all the big sprockets, leaving just a 14T. The snag with this approach is it will probably skew the chainline too far towards the outside.

 

[Jeremy Harris]

A big, yet surprising light, box arrived from Xootr this morning. I weighed it on arrival, and the box weighed 8.5kg (just under 19lbs). It was all pretty well packed:
View attachment 2

but unfortunately the couriers had still managed to give it a hard time (that's the front fork dropouts poking out of the box........):
View attachment 1

This package contains the complete frameset, inc all the parts for the bike except the wheels, BB, cranks, chainset:


After discounting the weight of the packaging it looks like the bike weighs about 6.3kg so far. The battery/controller box comes in at about 1.5kg, and the Speed Drive, cranks, chainring, pedals, chain and rear freewheel weighs in at another 1.5kg, so if I'm to stay under my self-imposed target weight of 16kg (around 35 lbs) for the finished bike then I need to ensure that the weight of the wheels and tyres is under 6.7kg, which seems possible. I'm certain I could come in under this weight if I were to use the Tongxin front hub/wheel I have, as that weighs just 3.2kg complete with a Marathon plus tyre, leaving me 3.5kg for a rear wheel and tyre, which would give me a kilo two spare. If I opt to use the BPM in a rear wheel then I'm going to be just over the target weight, but it'll still be a fair bit lighter than the 22 kg bike I have at the moment.

I think I may initially build the bike up with the Tongxin and see how it performs. If It does what I want then I may not end up using the BPM that's on order.

Just need to source a rear wheel now.

 

[NeilP]

Jeremy, had you considered a one way bearing, sprag bearing? Then you could make or Get made a collar to fit the bearing, and a sprocket of your choice
The bearing will act as the freewheel, probably allowing you to go down to 12 tooth

 

[Jeremy Harris]

Jeremy, had you considered a one way bearing, sprag bearing? Then you could make or Get made a collar to fit the bearing, and a sprocket of your choice
The bearing will act as the freewheel, probably allowing you to go down to 12 tooth

I hadn't, and it's a nice idea, especially as the sprag would be clickless (I hate clicky freewheels). I've bought a Shimano 16T that I'll start off with, but if the Tongxin front wheel motor I've got works OK, then I could get a BMX rear hub and go down to a pretty small rear sprocket, which might be an option. I've just ordered a rear wheel to take a standard freewheel, so I can get the bike going. If I decide to switch to the BPM hub (which bloody BMS Battery hadn't even despatched yet - two weeks delay and then the buggers email me to say they don't have the spokes I wanted in stock.............) then I'll have a look at what I can do to fit a smaller sprocket if I find I need it.

 

[NeilP]

I am doing this from the phone, in Oxford airport, waiting for medics to return so cant pass on my links, but I think SimplyBearings.co.uk had a good range

I wanted to machine a new collar to replace the threaded fitting on an Xlyte 5405 motor, to allow a 30mm axle to pass through the freewheel. Think I found a roller needle sprag bearing of 35 mm intenal 40mm external
Wall thickness would only be 2mm though, not sure that would be enough

Put that on a 35 OD collar on the hub casing and make a carrier to fit the bearing to take a home made 2 or speed 'cassette'

 

[Jeremy Harris]

I spent far longer than I should have faffing around making a tool to cut the 45 degree chamfers inside the BB, to accept the Speed Drive. I didn't have access to the Schlumpf special tool, so decided to have a go at making a simple one blade cutter. It worked fine, took maybe twenty times longer to make the tool than it did to cut the two chamfers in the BB.......................

Anyway, here's what I did, as it may help someone else. A got a bit of 1 1/2" alloy bar and turned part of it down so it was a snug fit into the BB housing. It needed to be slightly thinner in the centre to fit in the non-threaded part. I then set this up in the milling machine and bored a 45 degree 8 mm diameter hole and faced off around where the cutting edge would be, to give a bit of swarf clearance. The cutter was a bit of 8mm drill rod, ground to a sharp edge perpendicular to the axis and clamped in place by a long 6mm bolt. The bolt also acts as a handle to turn the tool. To keep a fairly constant pressure on the cutter, I turned down another short length of alloy bar, drilled it and added a bolt and spring to connect it to the cutter bar. Tightening the bolt increases the cutting force if needed.



The tool worked fine. I cut the drive side first, only going deep enough for the serrated face to fully engage with the chamfer, no more. For anyone doing this again, this means cutting the chamfer until the outer edge of it is about 38mm. I believe going too deep may be a cause of the BB not doing up tightly - there is very little leeway in the range of adjustment, maybe 1mm or so, as the end bearing has to be well engaged in the left side retainer. Once I was happy with the drive side chamfer, I cut the left side in stages, checking the fit with the Speed Drive and retainer at intervals. The depth of the chamfer on the left side isn't critical in terms of locating and locking the Speed Drive in place, but is critical in terms of getting the right total length. After three goes I'd got it spot on, and it tightened up well with maybe 0.5mm to spare.