Could just mount it on top but this would stop me being able to hook panniers over the top

 

I did eventually find pannier bags which go over my rackmounted downtube battery. Cheapos, but they did the job until I saw sense and got bike trailers instead. I can try and find a link for you if you're interested, they cost me less than a tenner (at the time).

Just spotted that, on the TBK spec, the motors' gear ratio is 10.5, whereas on the label it says 8.1.

I'm assuminmg this means that the rotor will spin slower for a given rpm. As this motor is specced at 48v/328rpm but I'll be using it at 36v to get 250, will this be a problem given the slower rotor?

Or am I overthinking this and should just go and dig the spuds up whilst it's not raining?

There isn't much you can change, so I would just continue with plan A.

Just spotted that, on the TBK spec, the motors' gear ratio is 10.5, whereas on the label it says 8.1.

I'm assuminmg this means that the rotor will spin slower for a given rpm. As this motor is specced at 48v/328rpm but I'll be using it at 36v to get 250, will this be a problem given the slower rotor?

Or am I overthinking this and should just go and dig the spuds up whilst it's not raining?

The motor RPM is the outside speed, so it'll be 260 rpm at 36v.

Could just mount it on top but this would stop me being able to hook panniers over the top bar.

I did eventually find pannier bags which go over my rackmounted downtube battery. Cheapos, but they did the job until I saw sense and got bike trailers instead. I can try and find a link for you if you're interested, they cost me less than a tenner (at the time).

 

Found it:

 

https://www.ebay.co.uk/itm/184538610881

 

 

Not waterproof without this:

 

https://www.ebay.co.uk/itm/153878744891

 

 

They still do the job in a pinch, despite having been used a lot.

Edited August 25, 20232 yr by guerney

Thanks Guerny, might consider those 'cos they obviously help you get up hills fast:rolleyes:

Thanks Guerny, might consider those 'cos they obviously help you get up hills fast:rolleyes:

 

Helpful and amusing. It's 3A extra that's increased my uphill speed, and the subject of another thread - I hope your bent doesn't get chased by people on foot uphill.

 

Those cheap and nasty pannier bags held up really well, though I totally understand if they're not the sort of low quality product you'd consider buying - the reason why I linked them, is because you asked a question, and because there may be better crafted products of similar dimensions and design to fit over a rear rack mounted downtube battery. Too much weight on the back didn't work out well ascending very steep hills, of course.

 

I'll ignore your posts and won't see them. I suggest you do the same. Despite apparently knowing a lot about bikes and batteries, you don't appear to try helping people out on many other threads, so I don't think I'll be missing much. The "Ignore" feature of this website is a good one.

 

Thank goodness for helpful members, who also know a thing or three.

Edited August 26, 20232 yr by guerney

Ooops! Shows how attempted humour can go wrong without the aid of facial and tonal expression.

 

Got everything in place now to start measuring for spokes and the learning can continue.

Using Grin's methodology and calculator, I've arrived at spoke lengths of 207 and 206mm. That's fine but, their graphic display reckons I'll get 72% tension one side and 28% the other to get the offset. The advice is to be as close to 50/50 as possible but nothing I alter (within measurements) makes any difference.

It's my first attempted wheel build and 72/28 seems a bit extreme, or am I suffering from information overload?

The difference in tension between the two sides goes up exponentially with the amount of offset. At 20mm offset, the spokes on one side would need zero tension. You can't really make a judgement until the wheel is in the frame. You can mitigate the offset by adding spacers to the axle on the brake side, but then you have to open the frame a bit more. That works very well for rim brakes, but you have to be a bit more creative with spacers for disc brakes to get the disc to line up with the caliper.

I used an Andra 40 rim and Sapim Strong spokes with head washers on a Shengyi DGW22C motor.

 

 

Grin's calculator worked a charm, I measured the rim carefully and the rest fell into place as shown. The wheel's beginning to creak and needs retensioning after 1900 miles.

Also, I forgot to mention that I've built many wheels with offsets, and always used the same spokes for each side. You have to be more careful with the calculations if you have single-walled rims, but i always use double-walled MTB rims that have loads of space between the nipples and the tube, so it's no problem when the spoke pokes through the nipple.That also means that you can use slightly longer spokes that makes the lacing easier.

I've redone the measurements and calculations and this is what it's come to:

 

https://ebikes.ca/tools/spoke-calc.html?hub=cust_d130_s44_o-8_n36_l138_h3_p22.7&pair=false&rim=cust_dia559_e535_lo2_ro2_w26

 

So it looks like left spoke at 208mm and right at 206mm.

The tension ratio still looks high but< I guess, it is what it is. If it wasn't for the calculator I wouldn't have a clue about it and would just use the wheel in ignorance of spoke tension. I'm guessing that so long as all spokes on one side 'ring' the same note, then it'll work. I hope.

> it is what it is

...and that's ideally not a jelly, if the ratio's really high you can end up with cracks around the nipples:eek:

Have a look at my lacing

I've redone the measurements and calculations and this is what it's come to:

 

https://ebikes.ca/tools/spoke-calc.html?hub=cust_d130_s44_o-8_n36_l138_h3_p22.7&pair=false&rim=cust_dia559_e535_lo2_ro2_w26

 

So it looks like left spoke at 208mm and right at 206mm.

The tension ratio still looks high but< I guess, it is what it is. If it wasn't for the calculator I wouldn't have a clue about it and would just use the wheel in ignorance of spoke tension. I'm guessing that so long as all spokes on one side 'ring' the same note, then it'll work. I hope.

 

If you look at AntonyC's calculation he has left side spoke elbows in and right side out, giving a much better ratio of 35:65. I've been trying to see if I could get it any better, but I can't. Incidentally, the drawing for the AKM-128CST has the flange spoke hole diameter at 129mm - not that 1mm is likely to make much difference.

AKM-128 CST Drawing.png (1253×838) (topbikekit.com)

If you look at AntonyC's calculation he has left side spoke elbows in and right side out, giving a much better ratio of 35:65. I've been trying to see if I could get it any better, but I can't. Incidentally, the drawing for the AKM-128CST has the flange spoke hole diameter at 129mm - not that 1mm is likely to make much difference.

AKM-128 CST Drawing.png (1253×838) (topbikekit.com)

That's right, you can reduce the offset a bit by bringing all the spoke out the same side of the spoke flanges. I've not done one like that, but it makes the lacing a bit more complicated. I think you'd have to build one side at a time - the brake side first, then the gears side otherwise you'd have to bend some of the brake side ones into all sorts of shapes to bring them to the rim.

 

What building sequence did you use, Antony?

That one sounds right.

Ok, I've changed the right side elbows to out and it's bought it to 35:65.

That's the same as yours Anthony and that worked out did it?

Thanks for the help everyone, you're helping to demystify the dark art of wheel building.

https://ebikes.ca/tools/spoke-calc.html?hub=cust_d129_s44_o-8_n36_l138_h3_p22.5&pair=false&rim=cust_dia559_e535_lo2_ro2_w26&relb=out&swap=false

With the tensions now at 35:65, I can't get it any better, and as Ryan's back from holiday, I'm going to order spokes.

Going to ordr all 208 as I figure 0.9mm won't make much difference.

Edited August 30, 20232 yr by Benjahmin

Ryan's out of stock of black Sapim strongs, so I've ordered from Bitex Hubs UK. Hope they come through.

Could have gone silver, S/S for a bit of bling.

True but it's a black rim, motor and cassette which will show up my bright yellow cycling jacket quite nicely methinks.

Me spokes have arrived and me nipples are soakin in oil. (Stopiiit!)

Realised I was short of a square driver, but I've found a red rawlplug fits nicely over the nipple top nut and passes through the inner wall of the rim.

Let the adventure begin.

Me spokes have arrived and me nipples are soakin in oil. (Stopiiit!)

Realised I was short of a square driver, but I've found a red rawlplug fits nicely over the nipple top nut and passes through the inner wall of the rim.

Let the adventure begin.

I screw a spoke a few turns into the top of the nipple, poke it into the hole, then twiist the poking through part of the nipple with my fingers to screw it onto the wheel spoke and screw it off the spoke that poked it through. I only have to do that with the second 18 spokes because the first 18 all reach through the rim so that you can screw on the nipple easily.

I am immensely chuffed to have built my first, apparently, concentric and true wheel and just to proove that it happened:

And here it is on the scratch built truing stand in concentricity mode, 'cos ya can't really turn a bent on it's back !:

 

Of course it's only now that I realise I haven't yet ordered a tyre, tube, rim tape or cassette.:rolleyes:

So to the interweb it is and get the wallet out - again.

Thanks to everyone who helped this process along. Hey, it's not such a dark art afterall.