Online Spoke Calculator for Hub Motors

[justin_le]

Hey guys, just finished this little javascript app which could be a handy reference for people relacing hub motor wheels:

http://www.ebikes.ca/SpokeCalc.shtml

I've got it currently listing the motors which we have in our shop and can accurately measure (Crystalyte, eZee/BMC, and Nine Continent FH205 series). The results with the the different rim choices cross check with our empirical spoke length 'look-up' table generally within a mm. So it seems pretty sound. Note that the Crystalyte 400 series hubs have two different flavours, the newer style rear motors with the offset flange system has a larger flange diameter and hence shorter spoke length than the original 400 series hub design, which is still used on their front (non disk/drum brake) motors.

I didn't bother implementing separate left and right side spoke measurements for rear wheels, in general just adding 1mm to the left side spokes and shortining the right side by 1mm does the trick for hubs that require dishing.

If anyone here has the measurement specs for other popular hub motors like the Bafang, BionX, etc., then I could add those to the drop-down list as well.

Justin

 

[HAL9000v2.0]

Great !!!

 

[Drunkskunk]

Wow.

Very Nice

 

[docnjoj]

Thank you Justin!
otherDoc

 

[drewdiller]

(Aside) You threw me for a loop there for a second with your IsNull() calls, I thought it was analgous to native isNaN() or something.

 

[nicobie]

Thanx Justin!

How would a person determine ERD on a double wall rim like a sun rino lite 26"? Where would you measure from?

Nick

.

 

[floatingdog]

Thanks! Nice job. Here are my numbers for a Bafang BPM and Sun Rhyno Lite 26". I included Spokecalc numbers for comparison. They match very closely. I haven't laced a wheel with these numbers yet, so I can't confirm they are right for this hub/rim combo. Please correct my Sun Rhyno Lite 26" ERD if you know better. I found differing numbers on the net. Also, please check my interpretation of the Bafang numbers based on the diagram below. I think I picked the right ones.

My Bafang BPM Thread: http://endless-sphere.com/forums/viewtopic.php?f=3&t=12582

BTW, the Bafang BPM is roughly BMC sized. I haven't seen a comparison yet.

Justin's program (Bafang BPM and Sun Rhyno Lite 26"):
View attachment 2

Spokecalc 2004 (Bafang BPM and Sun Rhyno Lite 26"):


Bafang BPM Diagram:

 

[floatingdog]

Justin,

Since you are being so generous with your help as always, what lengh spokes do you think I should order for the Bafang BPM / Sun Rhyno Lite 26 shown above? 196? Is there an optimal nipple length, e.g. 14mm that give me the greatest fudge factor?

Thanks again. Your tool promises to be the definitive resource if we can impose on you to catalog various common eBike hubs and rims.

John

 

[mwkeefer]

Justin,

Thanks alot man. Many people are realizing to get good quality on their hubs, better off building them up on their own but that begs the question of spoke length, diameter, tapered or not, etc.

The calculator atleast should answer some of these questions... nice!

-Mike

PS: IsNull(); actually checks for null or lack of any value which can happen on function failures or mathmatic whoops... might also just be for checking to see that the fields of the various input boxes are populated... would then be followed with a sweep of IsNaN(); to check for non numeric values before calling the calculation routine... it's prob std input validation = )_

 

[Zoot Katz]

Thanx Justin!

How would a person determine ERD on a double wall rim like a sun rino lite 26"? Where would you measure from?

Nick
.

Damon Rinard's Spocalc.XLS spread sheet does the calculations and has an extensive data base of rims and hubs. The spread sheet lists a few different models of Rhyno LIte 26"rims and comes with the advisory to measure the rim.
The manufacturers' website usually has the ERD of the rim as do many retail outlets with numbers copied from the manufacturers' sites.

I used 548 mm for my 26"Rhyno Lite and it calculated the spoke lengths to within 0.02 mm of Justin's Java and what I'd asked Adam to cut me thirty two. They fit perfectly. The Crystalite rim looks just like the Rhyno Lite but I've not measured one

It's simple to make measuring sticks and calculate nipple drop to get the ERD of an unknown rim.

 

[Zoot Katz]

Justin,

Since you are being so generous with your help as always, what lengh spokes do you think I should order for the Bafang BPM / Sun Rhyno Lite 26 shown above? 196? Is there an optimal nipple length, e.g. 14mm that give me the greatest fudge factor?
. . .

Russel recently pointed us to the Paralax nipple thats better able to accomodate more extreme angles.

Thread: http://www.endless-sphere.com/forums/viewtopic.php?f=9&t=13424&p=200950&hilit=nipple+angle#p200947

 

[lynchy]

I've used the following online spoke calculator:

http://www.sapim.be/index.php?st=spokelength

Used this and the spoke lengths were spot on. If you haven't done this before you need to realise that every 26" rim is not the same. A double walled rim will have a smaller spoke diameter (sorry might be the wrong term) than a single walled rim. Sheldon Browns website details how to determine the rims effective radius and from that and some simple hub measurements you can calc the exact spoke lengths required. Sheldon also explains very well how the whole process is done start to finish.

I've assemble 2 rims now, well actually 1 rim, just swapped hubs. It's quite time consuming and definitely requires a bit of a knack (which I'm a long way from acquiring) but is strangely satisfying :? :?

You might find the following series of online videos helpful, I did.

http://www.ehow.com/video_2363041_how-true-bicycle-wheel.html

Good luck :wink:

 

[floatingdog]

Thanks Zoot Katz. Maybe I can go cross 2 with those nipples.

 

[justin_le]

Thanks! Nice job. Here are my numbers for a Bafang BPM and Sun Rhyno Lite 26".

Hi John, great that's much appreciated. I've added the Bafang to the list now too.

Also, please check my interpretation of the Bafang numbers based on the diagram below. I think I picked the right ones.

You selected 35.5 mm as the flange spacing which is correct if the rim is laced with all the spoke heads facing outwards. When I did the measurements for the other motors I used the center to center flange spacing so that it would give the average length between head in and head out lacing patterns. I guessed that the center to center flange spacing on the Bafang is about 38mm. Minor detail, but just in case you're wondering why that one number is different.


Any other hub motor suggestions that people have dimensions for? I thought I still had a small Tongxin hub kicking around but couldn't find it anywhere in the shop to measure.

Justin

 

[floatingdog]

Thanks! Nice job. Here are my numbers for a Bafang BPM and Sun Rhyno Lite 26".

Hi John, great that's much appreciated. I've added the Bafang to the list now too.

Also, please check my interpretation of the Bafang numbers based on the diagram below. I think I picked the right ones.

You selected 35.5 mm as the flange spacing which is correct if the rim is laced with all the spoke heads facing outwards. When I did the measurements for the other motors I used the center to center flange spacing so that it would give the average length between head in and head out lacing patterns. I guessed that the center to center flange spacing on the Bafang is about 38mm. Minor detail, but just in case you're wondering why that one number is different.


Any other hub motor suggestions that people have dimensions for? I thought I still had a small Tongxin hub kicking around but couldn't find it anywhere in the shop to measure.

Justin

Thanks! Great tip on calculating the flange spacing. When I finally get my wheel built, I'll give feedback on the results.

Your work is really appreciated. Being able to select the actual motors / rims eBikers is a great service.

John

 

[pgt400]

Cool calculator. I have a golden motor and 20" wheel to lace. This should help, Thanks!

Phil