megaboo

Hi! I live in Finland and the summer has just started around here. I love to just cruise around on sunny days on the dirt roads in my hometown. I was reading one blog and I saw one post about automatic gears in bicycle. The price was near 2000€. It would be just awesome to have something like that in my bike. I thought, that I could make the same system myself. I'm planning to use speedometer in the rear wheel connected to arduino board wich tells the gear changing system to change the gear. When the speed increases, system changes to upper gear. When the speed decreases, system changes to lower gear. I planned to use magnet and reed-switch for the speedometer. I found one old cordless drill and removed the motor from it. Maybe I could use it for changing the derrailleur position? For first I'm planning to make the rear gears only automatic. Any opinions?

Monster Pete

I believe there's been a couple of bikes with an automatic transmission. They do mechanically what you suggested doing electronically- use a system of flyweights attached to the rear wheel to move the derailleur as your speed increases. However, a true automatic transmission should take into account the rider's input torque as well as the speed. Ideally you could be cruising in a high gear at low rpm, then when you kick down hard the system should change to a lower gear. Without measuring the chain tension I don't see how you'd do this. Personally I think the best gear changing system is the human brain, especially if you only have a rear derailleur or hub gear.

Chris_W

Very few people would be happy riding a bike with automatic gear changes. This sounds like a massive project to undertake when you don't even know if you'll like the outcome. Good luck!

megaboo

Well at least i'm going to try it. I also thought about making the system to calculate the gears from cranks, but I think it's easiest for now to do it with speedometer.

mmmdonuts

I thought Shimano had electronic automatic shifting on one of their IGH commuter/comfort type product lines. Computerized and programmable based on gear, speed and cadence.

AEO

it might be easier if you use an IGH like shimano nexus. Then you don't have to worry about shifting under torque load.

Esteban32696

Although I have never ridden one, I would not undertake so much work . I have seen one older model, called an " Autobike ," for same as low as $50. I know you are in Finland, but surely you could find a used one, somewhere.

https://phoenix.craigslist.org/wvl/bik/3001596282.html

bbmike

If you could put pressure sensors in the pedals you could measure how hard one is pedaling. Combined with cadence measurement you could come up with a formula when to shift up or down (for comfort or performance).

Another idea: use tilt sensor to measure how steep it is.

Another ...use gps for recording your preferred gear.

The biggest issue is for the system to know when you want to accelerate, and which is more optimal: shift down or let the rider increase the output.

Overall, it seems like the project is most suitable for ARM based tablet or a phone than adruino.

Simpler system could take the input from pedaling backwards (or pause) for a clue when to shift.

Shimagnolo

Generally, for such purposes, a stepper motor is used: https://en.wikipedia.org/wiki/Stepper_motor

Kimmo

Pretty ambitious project... IMO if you're thinking of using a cordless drill motor, you should prolly keep brainstorming...

Also, if you're going to use a derailleur, you should definitely use one of those Shimano ones with the pinch bolt mounted on a sprung arm, so the system can shift to a bigger cog when you're not pedalling without trouble; that's one less hassle to deal with.

Well, I guess you could just use a pot to tell the system your desired cadence. That'd make sense, IMO

fietsbob

Fluid coupled auto trannys in cars have bigger motors..

there has been the use of a tandem crossover crankset to use a
rear wheel electric motor out of the wheel, it driving a left side chainring
which in turn powers a , say a continuously variable Nu vinci hub.


some engineering courses useful, and an extensive production shop.

GeoKrpan

Automatic shifting is a great idea. One day it will be perfected and even "serious" riders will use it.

We already have electronic shifting, Shimano Di2 for example. Torque sensors are already in use on electric bicycles. I think all that's left to do is a little software.

Bill Kapaun

What might seem like ideal shift points when you are "fresh" WON'T when you are tired.

FBinNY 

I think you should hold off for a while. As electronic shift systems come down in price, you'll have half the job done for you, since an electronic RD eliminates the need for you to build the electro/mechanical interface. Using an electronic derailleur means you only need a speed sensor and logic board.

megaboo

Ok. Maybe I'll just pass this project. Went too complicated for me. Maybe I make my cruiser project single speed then.

oldbobcat

Every few years somebody comes up with a new solution to "the shifting problem." Even Trek took a stab at it with their Limelite model in 2008.

What we keep coming back to is better shifting systems, even using levers and cables.

FastJake

No computer will ever be able to tell me what gear I need to be in on my bicycle. I hate automatics in cars, but there at least the engine has a predictable and known power output.

GeoKrpan

The truth is that dual clutch automatic transmissions turn quicker lap times and get better mileage. It's way more fun to drive a stick, though, I would never buy an automatic.

A automated bike transmission could have several modes just like on cars.

tcs

Here you go, off the shelf, and at somewhat less than 2000€, too. Or here, for more.

tcs

They've taken a shot at this a couple of times: Coasting, Auto-D, etc. Never really caught on.

Homebrew01

This. Sometimes I want to be in a slightly "wrong" gear, either a bit high or low, so even if you offered me a free automatic transmission with no weight penalty, I would not want it.

Monster Pete

The easiest way is to use a rear derailleur only or an IGH. Then it's stupidly simple- move the shifter one way for a lower gear, the other way for a higher gear. I think a lot of the confusion about gear shifting stems from the front derailleur.