Note de ce sujet :
  • Moyenne : 0 (0 vote(s))
  • 1
  • 2
  • 3
  • 4
  • 5
Oran's NuVinci bike.
I have finally got round to writing about my own NuVinci bicycle. It’s a Raleigh Gritstone21 from the 1990s that I have owned since I was 15, so that’s 13 years now. I’ve clocked up over 16,000 miles (25,600km) since then. It has been modified over the years and I have done almost all of the maintenance in the time I have owned it. The frame gets repainted every year or two to keep on top of the rust as there is a lot of sea salt in the air during the wild winter weather we get.
[Image: hb2k.jpg]
[Image: v324.jpg]

NuVinci hub
In Sep 2011 I fitted the NuVinci hub. I built the wheel and did the installation myself. I kept the triple chainset that I had been using, a 48/38/28t, and adjusted the derailleur so that only the two larger sprockets were accessible. I have now got a double chainset 50/ 34t which results in a better overall range. The sprocket size is 18t giving a range of 24.5 – 130 gear inches. With a large difference in the sprocket sizes I needed a suitable chain tensioner. My solution was to modify a rear derailleur by replacing the top half of it with a piece of steel. This keeps to chain tensioning part of it and removes its derailing ability.
[Image: uhvx.jpg]

Other modifications

Disc brake
The first major modification I made to the bike was fitting a front disc brake in Apr 2010. I was getting fed up of replacing brake blocks and wheel rims as they were often getting wet and muddy. This was a challenge as the forks had no mounting bracket so I had to make one. I didn’t want to attach it low down on the forks as I have seen a photo of ones that have bent. It’s designed to transfer the braking force up to the old cantilever mounts. I over built it as I know safety was important and it paid off as it has never failed in the 8400miles (13,400km) I have done since. The weight is about 1kg as it is made from 4mm steel and double thickness in places. I don’t consider a rear disc brake to be necessary. I avoid using it and rely of the front disc if it’s wet and or muddy and this extends the life of the brake blocks considerably.
[Image: cnbn.jpg]
[Image: v5j4.jpg]

Tow hitch
As I don’t own a car a trailer is a very useful thing. I built my first one many years ago, the current one is my third. My first trailer had an overly complicated hitch so commonly seen on homemade bicycle trailers. For my second trailer I came up with the far simpler and very successful hitch shown in the photo. Although this type of hitch is used on larger vehicles it is for some reason rarely used on bicycle trailers. The range of movement is perfectly adequate although it does have to be a loose fit meaning it can rattle a bit. The trailer half is simply an eye bolt loosely fitted so that it can rotate freely. It’s survived all the abuse I have given it while towing trailers for miles off road and loads of up to 100kg.
[Image: 6brr.jpg]

When it gets dark here, unless there is a moon, it is total darkness. There are no street lights and no light pollution. Good reliable lights are essential so I made my own. I discovered that because my handle bars are straight and large enough in diameter to take a tube containing AA cells I could make a battery that fits inside. It’s possible to fit up to 10 Ni-MH cells in series, I’m currently using 9 cells as the voltage is close to that of a 12V lead acid battery. Having a 12V system has the advantage that there is a bigger choice of bulbs and it is also possible to power other devices and even a low wattage inverter.

The bulbs I use are MR16 spot lights. I started with a 1.2W LED version which provides just enough light dispersed over a wide area. Then a 20W halogen that is very bright but drains the battery quickly. The third is a 4W LED which is almost as bright as the 20W halogen and increases the battery life. I normally use the two LEDs and turn the 4W one off for approaching cars because they are pointing straight ahead not dipped. If I lived in a town this kind of light would be unsuitable but I rarely meet a car on my way home. I’m considering replacing the 20W with a 6W LED to give a really bright light when they are all on together but it’s not really necessary.
[Image: uxiv.jpg]

Future modifications

The ultimate way of powering all the lighting would be to have a dynamo of some sort. My plan is to copy the design of the very successful Sturmey-Archer Dynohub but make it slightly larger and use neodymium magnets. It would charge the 12V battery and have an output of 10 – 20 watts. As the power would be high for a dynamo I was planning to use a circuit to convert cadence into a voltage which could be fed into a charge control circuit. The idea is that the higher my cadence the lower the power generated by the dynamo. It would therefore do most of the charging when going downhill.

Samarium Cobalt magnets are becoming available in a bigger range of sizes so I could make a start on this project. I was reluctant to use neodymium because they corrode so badly and ferrite magnets lack the strength I need. Samarium Cobalt is a good compromise, they are as corrosion resistant as ferrite and have ½ - ⅔ the strength of neodymium which is a lot stronger than ferrite magnets.

Left side drive
This is something I have planned to combat the low efficiency of the NuVinci hub when climbing steep hills. This would involve fitting a left hand freewheel to the disc brake mount, something that has been done on motorised bicycles. The ratio of this single speed setup would then be chosen so that it was just above the lowest of the hub. Then when the hub is put into full underdrive the power will transfer to the more efficient drivetrain.
- Oran
Man you are one hell of a genius! Those modifications you made are simply amazing!
You must have the strongest legs on the island with all that weight you are carrying...

Did you braze-on the disc brake adapter ?
Si ça a déjà été fait, je peux le faire
Si ça n`a jamais été fait, donnez-moi juste le temps de trouver comment !

Thanks for your appreciation of my work.
The bicycle is a bit heavy (just under 20kg, 44lbs) but I like the feel of a heavier bike and the way it rolls. I’d probably win the prize for fittest cyclist on the island and I’m the only local person who rides a bicycle all year round.

The disc brake mount is only attached with two bolts both at the bottom. A small one into the mudguard mount and the second is the wheel nut. At the top it is only hocked around the cantilever post and is a loose fit. This is important as it allows the forks to flex. If I’m braking hard on a rough surface I can feel the forks stiffen up. Amazing how much flex there is in seemingly rigid steel forks.
- Oran

Atteindre :

Utilisateur(s) parcourant ce sujet : 1 visiteur(s)