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! 
no need
Edit*** Ermmm I kinda found that and alot more info on a build
hereCheers
MM
