Large Scale Central

Making servos throw more than 90 degrees

Electronics
#1

I wanted to enlist you electronics wizards, so I’m posting this - you may not bother to read the Live Steam forum.

http://www.largescalecentral.com/forums/topic/29381/servo-throws-over-90-degrees

Here’s a bit of research I did on making servos go the distance.

" The standard servo . . . is a 485, which if you look at the specs is a 90 degree servo when supplied the standard pulse range of 1 to 2 msec. The specs also state the 485 can rotate 180 degrees with a pulse range of 0.6 to 2.4 msec."

From other research, it appears the RX sends a pulse of width dictated by the TX. So it’s the TX that decides how wide the pulse and thus how far the servo turns.I think.

This one seems to be adjustable to 150% on all channels, for $35+$12 shipping. However, though it is 2.4Ghz it isn’t DSM2 so I’d have to use their RX and refit some locos.

https://www.aliexpress.com/item/Flysky-FS-T6-FS-T6-Mode-2-6ch-2-4g-with-LCD-Screen-Transmitter-with-FS/32511153650.html

Any comments?

#2

I’m not much help as I do all my servo pulses in code. Various software bugs have killed servos when I’ve sent too short or too long a pulse. Those little micro ones seem particularly sensitive, I’ve killed a bunch of them, so I cap mine at 1ms low, 2ms high and don’t deviate (at least on purpose). Nevertheless that’s good to know, I will have to get a 485 and play with it some. I want to incorporate live steam into my Protothrottle widget so that sounds like a good experiment.

#3

I had the same problem Pete, for an architectural model for work. Couldn’t find real answers. So I ended up using a 2:1 sprocket/chain.

But on the same project, I had linear servos that needed .5 to 2.5ms, which my usual controller wouldn’t put out. This unit did the job,

https://www.amazon.com/gp/product/B073XZH264

From the questions / answers, this single controller is said to have the same range,

https://www.amazon.com/dp/B07485M6PH

I don’t have it anymore (it shipped with the project), otherwise I’d test to see if it made any dif with the servos I have on hand. I don’t have the one you mentioned though.

#4

I will have to get a 485 and play with it some.

I found that many servos have specs that allow for 180 degrees. This Hitec HS85MG for example:

Max PWM Signal Range (Standard) 553-2300μsec
Travel per µs (out of box). 104°/μsec
Max Travel (out of box) 182.5°

I believe the Futaba S3003 was mentioned in another thread. Mine definitely does 170 degrees out-of-the-box with 100% throw.