servo question - analouge - digital setting. Does it really matter? - Page 1
Forum section: electronics / projects

author: lots o tots
author_rank: Contributor
timestamp: October 17, 2025 05:22:33 am
content: Hello,I bought a small 20X40 digital servo. I needed something with the highest torque I could get. I have the power to match the requirements. the speed doesn't matter.I bought one of those servo testers to use because the main purpose of it is to grip something with maximum strength and the potentiometer is good enough. However every time I plug in the servo tester, it defaults to analog mode rather than the 125,250hz. I was reading that it doesn't really matter if it's on analog or digital? I found this to be a little confounding.In any case, in my okay running this in analog mode? when I am running it, it will close a robot hand and I expect to run this thing close to or at its maximum torque.please let me know if I need to use a different controllerthanks

author: pcprogrammer
author_rank: Super Contributor
timestamp: October 17, 2025 06:52:31 am
content: If it is a servo like used in the remote control world the difference between "analog" and "digital" in the control path is the repetition speed of the control pulse, at least for as far as I know.The "analog" setup is based on the old remote control transmitters that use a 20ms interval and a pulse width of min 1ms to max 2ms to control from 0 to 180 degrees rotation. For the "digital" setup the repetition time can be faster, but the pulse width remains the same. For instance on 250Hz the repetition time is only 4ms. With this the servo can respond much faster to control changes than with the 20ms interval.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: October 17, 2025 07:45:13 am
content: What is a 20X40 servo?If you want a lot of torque, buy a bigger motorA 1kW servo motor can deliver around 9Nm (in intermittent duty) and at 3000rpm. And you probably want to gear that down a bit, but I guess you're looking for a smaller motor.But I guess you have one of those small RC / hobby servo's in mind that work with a 1.5 to 2.5ms pulses.The oldest version of "analog" servos' only had analog electronics inside. If it did not get a constant stream of pulses, then the motor would max out at one of the extremes. With the "digital" servos (uC inside) they remember the last sent pulse, and keep the motor at that position.The 1.5ms to 2.5ms pulse width is also a horrible protocol. It starts by throwing away 90% of the available bandwidth, and thus resolution. I once bought an S-bus compatible / clone servo. Later I found out that this also works with a pretty simple but convoluted protocol, and therefore did not do much with it. (It only has a position signal). Those small RC / Robot servos start to become interesting once you get into the full RS485 control in which you can adjust PID parameters for speed and position, can also do readback of parameters such as temperature, position and torque and much more. Those servo's are also connected to the same (RS485 duh) bus and that makes it much easier to control a lot of servo's. This type of servo is significantly more expensive though. But apart from the extra electronics, you get more. Build quality of the motor and gearbox is also better.If you want the best servo's for the lowest cost, then looking into those S-bus compatible things, and then reprogram the uC in it to add functionality may be a good compromise.Another difference is that the better quality servo's do not have a potentiometer, but a HALL sensor, and they can track rotation over multiple rotations. This is very nice if you want to add extra gearing to get more torque.But overall, the most important is that you realize there are a lot of different factors around servo's and the way they work. So think carefully about what your needs are and what hardware best fits it.

author: pcprogrammer
author_rank: Super Contributor
timestamp: October 17, 2025 08:53:08 am
content: 6 years ago I bought these URUAV Deluxe Line BLS3211 high torque brush less servos on Banggood. Can't find them there anymore, but this shop seems to still sell them.https://www.racer.lt/item/uruav-deluxe-line-bls3211-32kg-0-11s-7-4v-60-ip67-waterproof-brushless-digital-hv-metal-gear-case-servo-20643.htmlThey are really strong and with the motor being brush less they don't wear out like servos based on brushed motors.To control your servo there is no need to get another controller. In the analog mode it will work just fine. Most of the time you won't notice the difference in response.