First Ebike - GNG 250W Mid Drive

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flangefrog
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1 kW
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Joined: Jun 26, 2013 10:21 pm
Location: Auckland, New Zealand

First Ebike - GNG 250W Mid Drive

Post by flangefrog » Sep 24, 2015 7:41 am

Well this is a lot of text. I've tried to add lots of images to break it up. I want to get my build logs up to date after which I will post on some current issues and questions that I have. The timeline is not very accurate but who cares? Not me.

A couple of years ago I was looking to build a Velomobile. Mostly due to money issues this nothing had come of it but since then I rode my bike a lot more and made quite a few redesigns. After I saw photos of the New Zealand designed Pedego Stretch I decided a midtail cargo bike would be a much better option – at least for now.


I looked for a steel frame with a 1 1/8 head tube and found this DiamondBack frame on Trade Me (NZ local auction site).
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I took it the 8.5km to home by removing it's front wheel and tying it to the pannier rack of my mountain bike. I did this again (second photo) after I lent it to a friend for a week.
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At the same time I posted a wanted ad here on ES for a Nuvinci dev kit as I was still wanting to use the same drive as I was planning for the velomobile – a Golden Motor 500W-800W BLDC and Nuvinci Dev Kit in a mid drive configuration. I got an offer very quickly which I took up. I then came across a GNG 250W brushed mid drive kit going cheap on Trade Me. I knew it wouldn't be great but I decided to buy it to use temporarily. I went to Tumeke Cycle Space (a community run bike workshop) to install the motor.

The cycleway was flooded in some parts and although I was riding in the shallowest part the water was over my pedals.
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I used a standard crankset with a cartridge bottom bracket rather than the GNG freewheeling crankset as I didn't have any bearings or cups on hand to install the GNG BB axle. After returning home I took the bike out for a short test ride with two car batteries in series.
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It was very underwhelming and after coming back I tested the batteries with a load tester. Although I had tested the voltage before going one battery seemed to be faulty and was only putting a few volts out on a heavy load. It was already pretty late so I waited until the next day to try it out with a better battery. This time it was much better but still not great. It wasn't much easier to pedal than my Aluminium mountain bike up the hills but of course it was carrying much more weight. The motor was pretty noisy whether climbing or on the flat. Mostly the gears I think. I limited my trip to around 25km because I had no meter and didn't want to drain the car batteries. My pannier bags could easily take the weight because I had upgraded the rivets a while ago but they were developing holes from the corners of the batteries. As I didn't want to cycle the car batteries and reduce their life I decided that the test was over until I made a proper lithium battery.

Taking my first microwave (for my spot welder) and some shopping home
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First microwave wasn't big enough so I got a bigger one
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By this time the Nuvinci had arrived.
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I didn't have spokes yet so I bought some rims and painted them with aerosol enamel while waiting for the spokes to arrive.
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They didn't match the frame but I was planning to repaint that later. The matte primer worked well but the gloss paint was hard to apply and flaked off. Matte paint may have worked better but I think I might leave painting to the experts in the future and get them powder coated. By the time I had finished painting the rims the spokes arrived. 13G to 14g single butted for the Nuvinci and 14g for the front wheel.
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The Nuvinci was easy to lace in a single cross pattern.
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I went to Tumeke Cycle Space again and got some help truing the wheel. I also laced up the front wheel which surprisingly only took about 30min for a three cross pattern following the Sheldon Brown tutorial.
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The Nuvinci was fairly easy to get running although it took a while to create a usable shift map – I resorted to generating one with a custom spreadsheet.
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I used a bluetooth serial module and a modified bluetooth terminal on my phone to have a readout and change the shift map or manual shift position from my phone.
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The Nuvinci was powered by two small Vex Robotics 7.2V 2000mAh NiMh batteries in series. I did try to see if these would give any assist at all using the GNG motor but no go.
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I made a small 12 cell battery from old laptop batteries and was supprised I was able to go about 14km when using the motor just on hills.
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Just collecting some plants
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Not long afterwards I received 120 Samsung 29E cells from tumich after an 80 day wait for sea shipping.
https://endless-sphere.com/forums/viewt ... 0#p1078548
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I had started making my spot welder and had a small amount of nickel so I connected the two ten cell packs together and added four more cells to make 6s4p. This worked for a time on the GNG 250W (20A max) controller but when I tried upgrading to a 500W (28A max) controller it was hitting the LVC. I added four cells again for 7S4P which fixed that problem. I was able to go around 30km on this battery when using it mostly for hills and acceleration. I switched back to the 250W controller for some reason, maybe the 500W just wasn't lasting long.

I went to Tumeke Cycle Space again but just before leaving I managed to pull off the display connector from the Nuvinci controller. This is where I had connected the bluetooth serial adapter. Because of the shift map that the Nuvinci defaulted to I was stuck in highest gear with it powered or lowest gear with it powered off. I ended up having to pedal 11km standing up in high gear and the last 10km home in lowest gear which took a very long time. After that incident I managed to fix the connector and changed the default shift map to my usual one.
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It was pouring with rain while taking these photos. It creates a nice effect with the beam of light.
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On one of Auckland's new electric trains after returning from buying a new phone (first pic on my Sony Xperia Z3). I had several people ask about the bike including "Does pedalling charge the battery?" a couple of times.
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A break in the rain while shopping
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I used the bike for a few months like this but at the beginning of this month I found a cheap ebike on Trade Me that had suffered a battery fire. This bike which I call “crap-e-bike” because of it's bad performance, efficiency, looks and a multitude of other reasons was left unused in the bike shed with parts being picked off it every so often.

Here are some pics of the last trip it made.
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Although this bike wasn't great it definitely helped me get an idea of what I wanted in an electric bike. I also made several midtail cargo bike designs since starting this and I'll share those somewhere.

My second ebike build is documented here. I have a small problem with it (ok, a big problem) which means that I will be adding to this thread soon.

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