Author Topic: Auto gear shift  (Read 10886 times)

Offline MonkeyMagic

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Auto gear shift
« on: January 29, 2011, 12:41:29 PM »
Hey guys

I'm still pondering and preparing some bits and pieces to make a auto gear shift system using a standard derailleur part of my dual drive rebuild

I've searched around some forums, I may most post something on ES too but wanted to know if anyone had experience with robotics or RC builds?

Currently I have an Airpax K92121-P2 linear drive motor but I think it's not strong enough to hold the spring. And the fact I don't have a 4phase controller for this (they cost about $50 on their own)

I also have a PWM module to control a variety of brush motors, but this is probably not accurate enough...

The travel I need is about 15mm travel of the derailleur, so something needs to both push, pull and hold this.

Searching around I found this servo I think could be strong enough (or maybe overkill I don't know!) to do the job but don't have much experience with servos myself, but I think I understand I need to apply the rated power to the servo then pulse the signal pin an amount of times over a timed duration based on where I want the position. I will be controlling any of the methods with an IC. Has anyone made a big scale RC build that has moved heavy parts??

Room is not really an issue, I have plenty of space for the parts.

So I'm near set on the servo idea but wanted to know if anyone had a tension guage or a force meter to measure the pulling force needed to move a derailleur? I know it may differ between brands but a ball park idea would be good to know.

If you can be bothered reading, I'll explain a bit more about this:

Using a hall sensor wire from the internal controller, I can measure the pulses the sensor makes in each turn of the wheel. Here I can calculate the wheel RPM, wheel speed, distance etc. I know that a CA can do this, but I am also keeping a budget in mind ;) I want this to be a cost of around $50 if that, and no more. I'll detail more of this in my upcoming build post but this is a part I am stuck with in design..

Based on the RPM of the MP from the signal calculated,  pulse the linear stepper, or the digital servo to certain gear positions by pulling and releasing the derailleur caliper wire. I only have a mechanical front brake (rear brake is activated by a solenoid) and I don't physically run any cables from front to back. (my new design incorporates the cabling into the GM pack and everything plug n plays into that)

The design is for 3 main reasons;

1. Auto match needed pedal speed based on motor rpm
2. Use this for my cyclone chain drive top speed increase mod to enable chain drive at near full RPM of hub motors
3. Gives me true speed readings I can show on any display I like (7-segment LED display on handlebars etc.) and can log all of my data just like a CA

I've read up on Landrider and various other auto shift designs but they all are way too expensive to even think about (ranging upto $4.5K for shimano!!) and I've seen some bodgy stuff done with old drills etc. on bike trailers but I'm looking for something I can build and power myself :)

Anyway any tips would be great, and if anyone can measure the pull force of a derailleur spring [**The force necessary to move a derailleur ranges from 10lbs to 20lbs]  please post it up! :D no need :)

Edit*** Ermmm I kinda found that and alot more info on a build here

:D

Cheers
MM
« Last Edit: January 29, 2011, 03:51:35 PM by MonkeyMagic »

Offline MonkeyMagic

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Re: Auto gear shift concept
« Reply #1 on: January 29, 2011, 02:28:55 PM »
Awesome I thought someone had already done it woohoo

http://www.youtube.com/watch?v=m23kgfQIl7E

Guess that knocks that problem out of the way ;)
Anyway I'll build this then post parts you need in case anyone else wants to do this.

edit -- and this will be the end result ;) hehe
http://www.youtube.com/watch?v=-cbt96fgbpc&feature=related
« Last Edit: January 29, 2011, 02:37:44 PM by MonkeyMagic »

Offline Bikemad

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Re: Auto gear shift
« Reply #2 on: January 29, 2011, 08:10:12 PM »

Anyway any tips would be great, and if anyone can measure the pull force of a derailleur spring [**The force necessary to move a derailleur ranges from 10lbs to 20lbs]  please post it up! :D no need :)

If you're planning on using a close coupled servo, you could remove the spring completely and just use the servo to move the dérailleur in both directions.
It seems pretty pointless loading the servo unnecessarily simply to overcome the spring tension.

Alan
 

Offline GM Canada

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Re: Auto gear shift concept
« Reply #3 on: January 29, 2011, 11:12:40 PM »
Awesome I thought someone had already done it woohoo

http://www.youtube.com/watch?v=m23kgfQIl7E

Guess that knocks that problem out of the way ;)
Anyway I'll build this then post parts you need in case anyone else wants to do this.

edit -- and this will be the end result ;) hehe
http://www.youtube.com/watch?v=-cbt96fgbpc&feature=related


Interesting how he got that battery mounted in there. Why is he calling it an all wheel drive? Also how did he get that front derailer to freewheel like that?

Gary

Offline Bikemad

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Re: Auto gear shift concept
« Reply #4 on: January 29, 2011, 11:46:47 PM »
Why is he calling it an all wheel drive? Also how did he get that front derailer to freewheel like that?

Gary,

Not sure about the All wheel drive, perhaps it's because the motor drives all of the wheel including the gears. ::)

The Cyclone kit comes with a special chainwheel which has a unidirectional clutch (freewheel) mounted in the centre which screws onto the threaded boss on the inside of the special right hand pedal crank (the one shown on the left in the picture below).
This enables the motor to run fast without the pedals whizzing round and smacking you in the back of the legs when you can't keep up with it. :D


          ^ extended crank spindle is supplied for the bottom bracket.
    ^ crank fitted with threaded boss.

2 x 1000W motors shown below:


I think shorts or cycle clips would be mandatory with this setup.

Alan
 

Offline MonkeyMagic

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Re: Auto gear shift
« Reply #5 on: January 30, 2011, 02:25:35 AM »
Howdy

WEIRD - Sunday and my cyclone kit arrived today??? What the...

Anyway, that bloke has some kind of front drivetrain system - I've seen it on a motorbike before too.

See attached pic.

Today I'll measure up some spots for the motor.

Hey Alan - you were right ;) If you look further into that AutoShift blog, he had to remove the return spring and also cut everything off the derailleur that wasn't needed.

As for the chainwheel drive, I'm covering mine both sides and shouldn't really be an issue. I'll make sure I keep my leg hairs short hehe
« Last Edit: January 30, 2011, 02:29:13 AM by MonkeyMagic »

Offline GM Canada

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Re: Auto gear shift
« Reply #6 on: January 30, 2011, 12:47:52 PM »
Wow, maybe I'm just getting older and more sensible, but that looks like it is very dangerous.

Gary

Offline Bikemad

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Re: Auto gear shift
« Reply #7 on: January 30, 2011, 12:57:30 PM »
As for the chainwheel drive, I'm covering mine both sides and shouldn't really be an issue. I'll make sure I keep my leg hairs short hehe

Make sure you leave enough access to be able to refit the chain when it comes off.
And don't worry about trimming your leg hairs, the Cyclone's chain mechanism will soon remove any long ones that manage to get too close!  :o

Q. What side of a Monkey has more hair?
A. The outside. ::)

Alan