New GNG Crank-drive

[Deleted member 4366]

My new GNG crank-drive came today only 4 days from ordering to my door. It's rated at 400w for 48v and 350w for 36v. I've got the 36v version. The only difference from the 48v one is the controller.

With the kit you get the complete drive assembly - motor, mounting brackets, free-wheeling crank, chainwheel, drive chain, tensioner, controller and throttle. The controller has connectors for the brake switches and pedal sensor. I wouldn't think that the PAS would be much use. There's no instructions but it's pretty easy to figure out how to fit it, or you can use my guide below.

First you have to remove your cranks with a crank-puller.

Then remove the bottom bracket with a Shimano BB tool. Note that the right side has a left-hand thread. Some cheaper bikes have BBs that don't use the tool, but you can get them off with a hammer and screwdriver to knock them round, or some have flats for a large adjustable spanner.

 

[Deleted member 4366]

Once you've got the BB out, you mount the motor by holding it in place while you insert the new BB. One of the holes in the main bracket in mine had a bit of damage which prevented the BB from going in, so I had to file it a bit. It would be a good idea to check that the BB threads pass through the holes before attempting to fit it.

The new longer BB

Once the BB is in place, you thread a jubilee clip through the bracket and round the frame. I cut a bit of old inner-tube to protect the frame.

Bracket and motor mounted in place:

 

[Deleted member 4366]

Next you fit the free-wheeling crank arm to the chain-wheel and bolt it on, then you need to pass your normal chain over it and place it on the inner chain-ring, which I didn't do, so you can save time by learning from my mistakes. You can now attempt to get the primary chain on. I removed the bottom bolt under the motor to pivot it back so that you can get the chain over the sprockets.

Fit the other crank arm and the pedals and that's it for the drive unit - about half an hour's work if you're organised and don't keep losing your tools.

Now for the electrical stuff. Unfortunately GNG messed up with the motor connectors and provided two males. This would be a show-stopper for some, but I had some of those connectors cut off a BMSBattery kit, so just had to do a bit of soldering.

 

[Deleted member 4366]

I already had a throttle which plugged straight in, and I'd installed a 10aH Headway battery from BMSBattery for it's previous incarnation, so I was ready for testing. I've just got to tidy up the wiring and make a permanent installation for the controller, but I might switch the kit to another bike if I like it.

Here's the finished thing:

 

[Deleted member 4366]

Unfortunately the battery was a bit low, so I could only do short test runs.

It climbed our 14% test hill at about 7mph showing about 650w on the uncalibrated meter. The highest I saw was about 750w, so maybe a bit of shunt soldering will be required. The controller'sn supposed to be 22 amps, which would be neare 900w.

Its internal gearbox was more noisy than an average hub-motor, but it might need a bit of time to loosen up. It's only noisy under heavy load. Under light load it's very quiet. I would say that the power is similar to the 250w Bafang crank-drive that I had on this bike before. The gearing's different. so not easy to say.

I forgot to mention that the primary chain was very tight at first, which made a clacking noise. I knew from my other GNG that they soon loosen up a bit, so I sprayed light oil on it, which quietened it a bit. After the first test runs, it loosened off and went quiet.

The weight of the motor and controller is about 4kg, so not too heavy, and cost is about £280 including the quick shipping cost.

 

[BAH48]

Thanks for that - very interesting! Now I'm wondering if this will be a better bet than the old one.

 

[jackhandy]

Thanks, d8veh:

That'll be just the job when I fit my 250w kit, hopefully over the weekend.

Just one thing - There's no point wotsomever you giving build times, then saying "IF you don't keep losing your tools"!

It's a well-known fact that I live over a portal to a parallel universe, and that's where my spanners go as soon as I put 'em down

Except, of course, that mine's just an update on the brushless motor kit & not the rather tasty brushless one.

 

[oigoi]

Good write up and interesting kit - do you think this one will be better for wet weather riding?

 

[Deleted member 4366]

Good write up and interesting kit - do you think this one will be better for wet weather riding?

Definitely better than the one with belt and jack-shaft.

I had another brief test this evening and it seemed much more powerful. The only thing I changed was to charge uo the battery, but the change seemed too much for that. Unfortunately, it was too dark to see my watt-meter. I'll try again tomorrow.

 

[103Alex1]

Keep us posted on the performance tests - watching with great interest. .

Hadn't realized there was a primary chain between the motor and the chain wheel which I guess in theory must be breakable ... It must be well concealed on my current bike as wasn't aware of one at all thought it was some sort of cog-to-cog driven mechanism. Or I must be blind ! Is this primary and 'normal' dual chain system the same on all crank-drive units

They do summarize a bit more about the design of my current system which I'm trying to learn from (and I guess might be different ?) but haven't got my head around how most of it translates to the actual parts on the bike. Yet. :

Kalkhoff Impulse Riding | 50cycles Ltd

Also - is the bag on top of the rack housing the controller (albeit temporarily) and is that the battery underneath it ? Helps to get an idea of scale.

Thanks, d8veh:

Just one thing - There's no point wotsoever you giving build times, then saying "IF you don't keep losing your tools"!

It's a well-known fact that I live over a portal to a parallel universe, and that's where my spanners go as soon as I put 'em down

+1 .. those infernal invisible "borrowers" are in permanent residence wherever I seem to go ..... and still multiplying d8veh's job time estimates by a factor of 10-20 to give time to google some of the words. But the pictures are a touch and have really brought it to life.

 

[jackhandy]

Just a thought, d8veh - that back mudguard looks to terminate at just about the right height to chuck a goodly dollop of crud at the drive sprocket. Might be worth extending it down toward the bb.

 

[Deleted member 4366]

Different crank-drives use different methods od driving the crank. In most cases, the motor runs faster than the crank, so there has to be a reduction system to teduce the speed. Kakhoff, Panasonic and Bosch use an internal gear system. Most DIY attempts and some kits use a primary chain. Some kits drive the normal chain directly, and the Sunstar uses gears.

This bike is only a lash-up to see how the motor performs. If I like it, I'll do a more permanent installation, probably in a different bike. The controller is located in that bag.

 

[Deleted member 4366]

I just revived this thread because I have just revived the bike.

I had fitted a 30 amp controller with LCD display that made the bike a lot more pleasant to ride, and I started to really like this bike. Unfortunately, I was lazy one time, setting off in top gear. The massive torque from the motor at 30 amps smashed the drive sprocket. I could only get a 13T replacement instead of 9, which completely changed the feel of the bike, and I didn't like it any more so it got confined to the shed.

Recently I noticed the 9T sprocket as a spare part on the GNG website, so I bought one and resurrected this bike. I have now fitted a Nuvinci N360, It's now perfect. The controller uses speed control, so when I pedal on level one, it controls the crank speed. The Nuvinci gear-changer therefore becomes a throttle, since power depends on crank speed. Each PAS level on the controller affects the power and speed, but I just leave it on level 1. Level 5 is OK for the open road when II just want to maintain a higher speed.

I can pedal comfortably at 25 mph, and it still has a very low bottom ratio for hill-climbing.

I can recommend the Nuvinci as being a good match for any crank-drive, but especially for those that have speed control controllers (Chinese ones).

 

[averhamdave]

Dave, I'm struggling to follow some of this but nothing new there.
Looking at the Nuvinci it seems you've retained the derailleur arm with the single sprocket? Is that to maintain chain tension?
Also is the nuvinci also fitted with a hub brake?
Finally we spoke the other day and at that time you were still firmly of the opinion the hub motors were still better than crank drive (in a DIY situation). Does this upgrade change that view?

 

[Deleted member 4366]

Good questions. Sorry I missed them, but somebody pointed it out in a PM.

The derailleur is for chain tension because of the vertical drop-outs. You can buy better chain tensioners, but this one was already on the bike, so what the hell!

The Nuvinci comes with the 6 holes for a normal disc brake. I'm using rim brakes at the moment.

The GNG reduction gears make a lot of noise. People can hear you coming, which is handy sometimes, but you won't be kidding the lycras. You have to oil the drive chain before very journeyand adjust the chain tension from time to time.

I think overall, a 500w hub motor with cruise control or 5 levels of PAS is still the best. It's so easy and predictable. The GNG makes a nice touring bike, but i'm not sure whether it's as efficient as the hub-motor. I would have easily done that recent 50 mile journey with the CST, but I don't know if the GNG battery is playing up. I'll try a different one next time.