Xiongda Motor?

[top drive]

12mm plate swing arm ?

that will be flexy as sin and heavier than hell.

They are tubular for a reason these days.

As above that bike will fetch a pretty penny on retro bike most likely - Id flog it and buy something thats fit for purpose rather than mashing it up.

If you must make a rear end then braze together something out of tubes - the hardest part is getting the tubes notched correctly.

 

[Slimjim]

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.

Not a bad idea, water jet cut plates that tab together and some welding and you can incorporate all features.

As per comment above, a swingarm made from even square section tubing, like the old Pace RC100 frames, would probably be stiffer but more time consuming.

Look forward to seeing your plans develop.

 

[Slimjim]

Following on from Top Drives comment, one of the reasons being that whilst plate would be easy to manufacture from, and plates are vertically stiff, they do not withstand twisting very well. But a tube is good at resisting twisting forces. So if you make a truss from tubes (round or square profile) , you can achieve the vertical stiffness from the structural layout of the tubes, and the torsional stiffness would be a combination of the structure, and the material (the tubes).

 

[Slopes]

Thanks guys. I've been looking at some alu rectangular tube - 6063T6. I'm thinking maybe 80mm x 20mm with a 2mm wall. I'll weld some horizontal dropouts onto these (for wheel adjustment to take up chain slack) and work out what's needed for torque and disc brakes (I've heard there is a conversion kit for older bikes with only V brake mounts).

The good news is my frame is now in the country... although I've just discovered I'll have to pay duty on it ...I always believed second hand goods were exempt.

Asked in my local bike shop today about lacing a rear rim with motor hub... they said it's no problem and they'll do it for £35 - which seems like a very good price to me.

 

[top drive]

Unfortunantly anything that has not had uk tax paid on it before is liable, new or used unless its from within the eu,

Making a rear end with adjustable drop outs may not be as simple as you.

Because the rear suspension moves the rear axle through an arc the distance between chain wheel and cassette changes through the Arc

 

[Slopes]

Top drive - yes, I can see the point you're making. Even though the rear axle will essentially be a single gear, its arc (from the chain crank) will still diverge from the arc of the swing arm as suspension is brought into play. It therefore seems likely I will require some form of chain tensioner to compensate for the small difference this will cause. Thanks for mentioning this.

 

[top drive]

yeah because the pivots not concentric with the centre point of the front chainset - not many FS bikes are due to bearing issues mind.

Try shimano alfine sprung tensioner - or for the cheapo option use a rear mech locked out with a bit of cable - if you stick the head of the cable into the barrel adjuster and pull mech to desired position and tighten cable to hold it - no need for a shifter

 

[Slimjim]

Are you going for this kind of swingarm shape?

 

[Slopes]

Are you going for this kind of swingarm shape?

Here's a technical drawing I found of the K2 (which has been very useful for planning out) and I'd like to shape the swing arm as closely as I can to its original shape. That's not gonna be entirely possible with rectangular tubes - and I suppose I could build the arm as a frame of round tubes (following the contours of the original) and weld a tapering 3mm flat plate onto each side.

I've seen pictures of the same K2 bike with an alu swingarm (obvious from the weld lines)... maybe Proflex brought this out to deal with cracking problems in the CF version?

 

[D8ve]

Their is nothing to stop you doing a straight swing arm is there?
That would simplify the design perhaps even lighten it?then an offset mount for the shock.

 

[trex]

straight arm would fracture at the point where the spring is attached.

 

[top drive]

im still struggling with the aspect of this being cost effective ? or is there an emotional attachement to these proflex frames

 

[Slopes]

A straight swing arm in the rectangular tube would be the easier option (and the preferred one in terms of my metalworking abilities). Although I'm not sure if a straight tube would clear the crank/BB.

 

[Slopes]

straight arm would fracture at the point where the spring is attached.

trex - is there anything I could do to prevent this happening? Such as raising the height of the shock mount to its original position and welding the two arms together with a hefty central 'shoulder'?

 

[Slopes]

im still struggling with the aspect of this being cost effective ? or is there an emotional attachement to these proflex frames

So far it's shaping up to be very cost effective. And - from a design point of view - I like the look of the bike... it's one of a few from that era that lends itself to conversion (CF swingarm notwithstanding).

 

[chris_n]

Get your swing arm fabricated into box sections from flat plate then no need for the heavily loaded weld just in front of the shock mount. You could then carry the side plates on to form the dropouts.

 

[Slopes]

Get your swing arm fabricated into box sections from flat plate then no need for the heavily loaded weld just in front of the shock mount. You could then carry the side plates on to form the dropouts.

chris_n... that sounds like a good solution, but I think it'd be beyond my abilities - would like to keep the welding I'll have to do to a minimum.

 

[Slimjim]

What equipment do you have to cut/machine/weld/design with?

 

[Slopes]

Well, a friend has a TIG but to be sure, I might ask in the local cycle shop if they can weld alu. If I go with rectangular box tube, I can ask the supplier to cut pieces to the dimensions I supply - or cut them here on my mitre saw. As for the initial design, I'm pretty good with Fusion 360... so I'll start by making a precision drawing of the new swingarm, taking measurements from the old CF one (once the frame actually gets delivered!).

 

[Slopes]

I have the frame now- looks in great condition... barely used, if at all I've decided to keep and use the carbon swingarm for the time being - as rebuilding the item in alu will be time-consuming and tricky - with its various angles. I'm not intending to use the bike off-road at the moment so I can gently test out the existing backend with the motor fitted.

The dropout gap is 135mm - as bending the arms is out of the question, I'll opt for a version of the Xiongda hub at that width. Presumably, if I'm limiting myself to a single gear at the back, I could fit in a disc brake too (?)... if not, I'm ok with a V brake on the back with a disc on the front forks.

The Xiongda website appears to be down currently so I do hope they haven't gone out of business (has anyone had any recent dealings with them?). I also note that Panda Bikes has stopped selling this product - which is a shame as I was very templed to buy the whole kit from them.

I have to decide upon 36v or 48v. I definitely want to keep within the 250w legal limit, but also want the best performance I can get - any help with a good overall set-up would be welcome.