KHS Crest with modified GNG v1.1 mid-drive

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meelis11   100 W

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Location: Tallinn, Estonia

KHS Crest with modified GNG v1.1 mid-drive

Post by meelis11 » Apr 10 2015 3:23pm

Hi,
I have this bike equipped with GNG mid drive almost 2 years already and better late than never...I am making build log here :)
Maybe others can get ideas from my modifications and vice-versa.

Battery: 44V 10Ah LIPO (4pc of 5Ah 6S Zippy LIPOs, in 12s2p configuration)

stats so far (ebike conversion made in july 2013):
distance traveled: about 5000km
primary belts broken so far: 5
longest belt life: ca 1500km (first belt)
shortest belt life: ca 290km
average belt life: 800-900km

then I had enough and made my belt mod (making new post with details below) . It SHOULD last now much longer, well see...(only 400km riding done after mod)
Attachments
DSC_1915-.jpg
Currently looking like that
Last edited by meelis11 on Apr 19 2015 7:03am, edited 2 times in total.

meelis11   100 W

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Location: Tallinn, Estonia

Re: My KHS commuter with GNG v1.1 mid-drive and modification

Post by meelis11 » Apr 10 2015 3:55pm

One of the first mod I made was to make front chainrings bigger.
That way I can get better cadence and can bedal along with faster speeds without using small 11t sprocket in rear cassette.

So I bought 53T chainring and bolted it together with 38T chainring (was inner chainring before).
That 53T replaced 44T secondary reduction chainring and 44T moved to inner place - to drive rear wheel.
SUCCESS! :)
I had more motor reduction (max crank speed in full throttle 147rpm -> 122rpm) now and I was also able to use 13T rear sprocket instead of 11T when commuting 30-35km/h
Image
Attachments
bike.jpg
44T vs 53T
bike.jpg (98.43 KiB) Viewed 305 times
sprocket2.jpg
Drilling holes so I can use old 38T chainring as adapter
sprocket2.jpg (119.99 KiB) Viewed 305 times
sprocket3.jpg
result after mod is complete
sprocket3.jpg (145.61 KiB) Viewed 305 times

meelis11   100 W

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Posts: 116
Joined: Jul 30 2013 5:29am
Location: Tallinn, Estonia

Re: My KHS commuter with GNG v1.1 mid-drive and modification

Post by meelis11 » Apr 10 2015 4:31pm

This post is about battery box making.
Wanted battery box that is inside frame triangle and made of aluminium - so it gives some extra protection being hard case and can hold fire/flames inside in worst case scenario (its LIPO you know!).
I did not want to fill all triangle because:
a) I dont need that big box - my batteries can fit smalles box too. Probably can add there 5Ah extra if needed in future. Right now controller and DC-DC converter is there too.
b) I can keep bottle holder
c) I can add child seat holder around saddle tube
d) I can use U-lock to lock my bike around upper tube

Its just much more practical that way - it is commuter bike.
Attachments
batterybox_making.jpg
Battery box making. I had to make it thinner from top so it does not interfere with my pedaling.
batterybox_done.jpg
Battery box done
batterybox_inside.jpg
Inside battery box

meelis11   100 W

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Location: Tallinn, Estonia

Re: My KHS commuter with GNG v1.1 mid-drive and modification

Post by meelis11 » Apr 10 2015 5:09pm

After fifth belt broke, I decided that I need to do something about that idler pulley - belt is so agressively wrapped around it and like that probably weakens belt inner structure and then it breaks.
Stock belt length is 475mm (475-5m-15), I ordered two belts with 460mm length (460-5m-15), so it is 15mm shorter.
Needed to drill one extra hole to idler arm and that is it :)
I dont know yet if this mod makes belts last longer than 800-900km but It should be better. All my belts just broke in commuting and not ion full throttle - so their inner structure was probably weakened by that hard wrapping around small diameter idler.
Attachments
belt_mod2.jpg
Drilled new hole to pulley arm (pic is taken without belt protector cover, later installed it back)
belt_mod2.jpg (181.73 KiB) Viewed 1487 times
belt_mod.jpg
In future planning to use these bigger pulleys (temporary bolt in this pic is too long)
belt_mod.jpg (168.51 KiB) Viewed 1487 times

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Overclocker   10 kW

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Re: My KHS commuter with GNG v1.1 mid-drive and modification

Post by Overclocker » Apr 19 2015 1:54am

hi, what brand belt do you use? 900++ kms pretty good.

btw what terrain do you ride?

meelis11   100 W

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Location: Tallinn, Estonia

Re: KHS Crest with modified GNG v1.1 mid-drive

Post by meelis11 » Apr 19 2015 7:01am

Overclocker wrote:hi, what brand belt do you use? 900++ kms pretty good.

btw what terrain do you ride?
First original belt was Gates HTD, that lasted 1500km.
Then four belts were Goodyear Whitehawk - they lasted 800-900km max, not more. Worst one was only 270km :S

And that is commuting in mostly flat ground/pavement.

Now I bought two 460mm length belts (OPTIBELT OMEGA) and reduced wrapping around idler pulley. I hope they last longer now than 800km.
I am on my first belt, distance covered ca 400km, so cannot answer right now if mod did any good.

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r3volved   100 kW

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Re: KHS Crest with modified GNG v1.1 mid-drive

Post by r3volved » Apr 20 2015 7:31am

I'm definitely interested in hearing more progress on this simple mod. I've thought about a 460mm as well but never took the plunge.

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Overclocker   10 kW

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Re: KHS Crest with modified GNG v1.1 mid-drive

Post by Overclocker » Apr 20 2015 8:11am

but i'm not sure if decreasing wrap is a step in the right direction... i hope meelis11 would keep us posted...

anyway if that fails you might wanna try an 18T pulley for more tooth engagement. but then it would totally screw up the already bad reduction. so you'll need an even bigger belt pulley and chainring :twisted:

meelis11   100 W

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Location: Tallinn, Estonia

Re: KHS Crest with modified GNG v1.1 mid-drive

Post by meelis11 » Sep 22 2015 1:17am

Overclocker wrote:but i'm not sure if decreasing wrap is a step in the right direction... i hope meelis11 would keep us posted...

anyway if that fails you might wanna try an 18T pulley for more tooth engagement. but then it would totally screw up the already bad reduction. so you'll need an even bigger belt pulley and chainring :twisted:
Quick note. In august I changed belt after 1100km riding. Actually it did not broke, but it seems to have stretched at bit that I did not have way to tighten it with stock tensioner bearings. I still use stock, but in previous post I have pic where I was planning to use bigger bearings (=bigger idler pulley). Planning to use these soon.

Anyway, little-bit less enganged teeth is not a problem - I have never skipped tooth on belt with 30A peak controller and even with 35A peak I lately tested. My chain jumps sprocket teeth on back cassette even with new chain and cassette lately - maybe I need more tension on chain - probably I will make chain one link-pair shorter and reduce amps to under 30A.

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