No worries Robert The wife thinks I have too many items of Z scale rolling stock anyway. Our Brooklyn (10) totally disagrees! Best wishes Kev Oh, In other news it looks as if I might be in California in late May to get my mom sorted out now she is in care. Hopefully it will be better than last time I came over for the last days of my dad to find wildfires, mudslides, 101 and the Pacific coast line blocked. Did make a lot of friends with the Amtrak guys though as I have had experience of lines cut by floods in the U.K and how we kept trains running on the Cumbrian Coast when the Derwent Bridge went down Pacific Coast line just after re-opening at Goleta Funny how the TV news was more concerned with Oprah Winfreys' house getting totalled than anybody elses problems Kev
Witnessed, Verified and Testified. Watched Rob build them much faster and sharper details. Loaded up his new Sawmill module. random roads or years makes for realistic staging. Then AZL dumped a bunch on the market
I got 2 sellers Linear servos, (Rob’s Amazon link and a second vendor). Both servo mechanisms identical but different color circuitboard, different color cable and connectors. Are used the standard large GST connector and two different servo controllers. The linear servos constantly rattled and servo sorta smooth. Hi cut off the micro GSD connector to connect it to the same servo controllers with the same servo noise so two different servo suppliers for servo tested all noisy jittery. I got my solo scope out and the jitter noise is roughly 40 mA and during servo motion it’s almost 300 mA. I’m not putting this on anything that’s wood. These are certainly designed for the lightest, lowest mass and zero friction applications. I didn’t even bother getting out my tension gauge to test for even micro Oz of torque.
I too have observed they jitter a lot. Initially I was excited to find servos this small. but I too am rethinking them. I think it's because the pot is no good that they jitter, struggling to reach a resistance output from the tiny thin film pot.. These need an optical encoder strip or some other optical position feedback to be useful, but I feel they could drive semaphores and crossing gates with an Arduino, because you can configure the resolution of the potentiometer resistance to be a range, and the crossing gates would stop at slightly different positions up and down, but be close enough. An example is the code lets you input the resistance range of your servo from say 900 ohms to 2000 ohms as the range of travel, and then your code would break that into 255 steps. So if the servo is commanded to position 128, the resistance can be within 4 ohms of target. The pot is so small that it might never be satisfied and chatter. However if you change the code to break it to 16 steps the pot resistance window goes to 70 ohms window, and it might not chatter. The problem with the chatter is that as the servo chatters, the wiper in the pot is grinding away at the resistor material, so they have a finite lifespan as Kim pointed out earlier. Hence, the ultimate solution is an optical position feedback system.
Even if you put a 270 degree and only use 15 degrees, I would place a limiting shroud in case it goes berserk, looses position or good-ol' power up's, so it doesn't rip the arms off, particularly a 3D print mechanism. Or at least build an add-on gear reduction to so the same (Bonus: they'll move slower too)
As I mentioned I use the Deoxit F5 fader lube to stop those jitters in my flying models. But if these servos are not suitable for these applications it would be a waste of $. It is sounding like they don’t have the precision or power for this machinery. Too bad if that is true.
Also these tiny no inertia motors are difficult to control with low rpm. Thats also why they jitter, they go high rpm, overshoot, undershoot and keep jittering. Its best to find a smooth operating servo thats small enough. There might be good ones in micro or sub-micro size, not seen a good one in the nano size. These are common names used and does not reflect the actual size. Its good to experiment. One thing for sure is price reflects quality in these, there is a huge RC market that has beaten this servo to perfection. If you check out the rc groups you will get an idea. Sent from my iPhone using Tapatalk
Rob, what about our Bay Area locals Model Railroad Control Systems. While large (little more than the typical servo), they have a linear drive conversion. So you create your PWM pattern to do the effects. https://www.modelrailroadcontrolsystems.com/mp1-version-2-switch-motor/ https://www.modelrailroadcontrolsystems.com/mp5-switch-motor/ You likely only need the MP1 unless you need the DPDT of the MP5
Hadn’t thought of this before but in RC world “digital” servos are generally considered to be more accurate with better holding power at all positions and nylon gears are more precise with less gear lash than metal geared ones.
