stronger Servo?

[visitor007]

So I've build the Shift4Me. It's great! It really is a great tool - my gears are shifting automatically and the result to me (riding comfort) is very noticable. I get to my destination with more easy than before.
But I have a situation: after some time (it happens mostly aften a 10km ride) suddenly the servo moto is acting up: it is moving back and forth randomly. My battery indication is not flashing (so battery should be fine).
Anyone have any idea of might be causing this??

When the problem occurs: then i turn the power off, wait two minutes, everything is back in 100% working order. Then again after 5-10kms, the problem re-occurs...

[Jan Oelbrandt]

the servo moto is acting up: it is moving back and forth randomly. 
Anyone have any idea of might be causing this??

It sounds like the servo is having problems handling the torque.
I've seen it before happen that the recommended servo (PowerHD 1510MG) has this behaviour if it gets overheated, caused by heavy load. 
Is it a derailleur or hubgear on your bike? Some derailleurs have quite a strong return spring, you should also check that the routing of the pull cable is fine (no obstacles, no sharp bends). And of course, derailleurs need maintenance especially if you're riding in dirty road/weather conditions. I mean: cleaning & lubrification.
What you could do, is check what amount of torque your system is requiring. I've used a luggage weight balance (like this one) to measure it. Should be in the range of 5-15 kgs, no more.

When the problem occurs: then i turn the power off, wait two minutes, everything is back in 100% working order. Then again after 5-10kms, the problem re-occurs...

That's why I'm thinking it's an overheating problem: after letting it cool down, problem is gone...
Keep us posted!

[visitor007]

I've seen it before happen that the recommended servo (PowerHD 1510MG) has this behaviour if it gets overheated, caused by heavy load. 

oh, so maybe I need a stronger servo?

Is it a derailleur or hubgear on your bike?

It's a Shimano Alivio 9s derailleur.

Ok thanks Jan, I'll try to measure the torque and see what happens

[visitor007]

Ok, update: I'm reading 6kg of torque when the derailleur is aligned at sprocket 2-3 (1= smallest sprocket) and then it quickly goes up to around 17kg when reaching sprocket 4-5 and stays there up till sprocket 9.

[Jan Oelbrandt]

Well, 17kg is the maximum stall torque of the PowerHD 1510MG (which I guess you're using, you haven't specified that yet). If you're sure your derailleur is working as it should and the flow of your derailleur cable is fine, you could try an other servo with a higher torque spec.

[visitor007]

Thanks... I will double check everything and let you know. (and yes, indeed using the 1510MG)

[visitor007]

since everything was good with my derailleur (as far as I could tell), I ordered a stronger servo. I chose the PowerHD LF-20mg, which according to specs should pull 20kg/cm. It is 25% more expensive than the 1510mg (33,50€ vs. 27€). I'll see how it will turn out and let you know

[visitor007]

So I installed the new servo and calibrated the setup. Yesterday I did a 30km ride. Very hilly terrain, so the servo motor has got a lot of action (lots of gear changes needed) Got home after 1h40m with everything still working 100%. So far so good!

[visitor007]

So far, the LF-20MG is outperforming the 1510 by far! It's shifting quick and very precise. And it seems it's drawing a lot less current, my batteries are lasting a lot longer than before.