looking for 5Nm, low RPM servo motor - Page 1
Forum section: electronics / projects

author: dequo
author_rank: Contributor
timestamp: February 17, 2011, 02:33:20 am
content: Hey, i need a servo motor that can provide 5Nm at very low rpms, i have looked through rs electronics catalogue and all theirs are rated for high rpms, about 4000. I only need very low speeds - about 1-10 rpm would be fine.any suggestions? thanks

author: Jimmy
author_rank: Regular Contributor
timestamp: February 17, 2011, 03:38:05 am
content: Servo motors are rated at a max speed you can make them run at 10 rpm if you like. Servo motor and Drive are not cheep. What sort of accuracy do you need with the motor and what is it for.

author: dequo
author_rank: Contributor
timestamp: February 17, 2011, 03:48:49 am
content: The motors will be attached to a lead-screw to lift an ~85kg weight to a precise angle. I need at least 10 degree accuracy. The high rpm motors are expensive and i would be paying for unnecessary power.

author: GeoffS
author_rank: Unknown
timestamp: February 17, 2011, 04:51:58 am
content: Depends on what you consider expensive.Have a look atKeling, they provide steppers and servos for CNC use..

author: dequo
author_rank: Contributor
timestamp: February 17, 2011, 05:06:55 am
content: thanks geoff. i guess what im really after is a geared servo motor. although a high rpm one would work, it just seems like a waste of size and powercould i use a stepper motor for this? im not sure if a 'holding torque' of 5Nm could turn a 5Nm torque?

author: JohnS_AZ
author_rank: Frequent Contributor
timestamp: February 17, 2011, 04:25:49 pm
content: Why not use a jack screw? ( AKA Linear Actuator )https://www.surpluscenter.com/item.asp?item=5-1679-8&catname=electric

author: Zero999
author_rank: Super Contributor
timestamp: February 17, 2011, 05:25:29 pm
content: You need a gearbox to reduce the speed to the required level and get the torque. What's the maximum/minimum speed you need?

author: dequo
author_rank: Contributor
timestamp: February 18, 2011, 01:50:47 am
content: i cant use a linear actuator because this will be installed into an existing actuation method which would not support itmax speed probably 10rpm, min 1rpm. I am looking into using a dc motor + gearbox + encoder + motor controller.maybe a motor like thishttp://australia.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=4540861its annoying that nobody makes servo motors for this application,there are hobby servos -> extreme industrial servos with nothing inbetween

author: Jimmy
author_rank: Regular Contributor
timestamp: February 18, 2011, 03:31:17 am
content: QuoteCome on this isnt true you can buy heaps of different sizes.I can get servo's at 0.0955, 0.159, 0.318, 0.637, 1.27, 2.39, 3.18, 4.90, 6.36, 9.80, 12.6, 15.8 Nm off one page of a catalogue.The 4.9 Nm Servo is rated at 1.5kw which is heaps of powerWhen you say you have to lift it to a precise angle do you have another piviot point that holds weight. How did you caculate how much force you would need? Can you borrow a torque wrench and test in real world what you would need

author: dequo
author_rank: Contributor
timestamp: February 18, 2011, 03:42:55 am
content: thats true but as i mentioned, those servos would be non geared and rated for 4000RPM, cost $1500.i dont want to be paying for unused power capabilities. i need one rated at a lower power and with a high gear ratio like the dc motor i linked to (only $60)yes there is a pivot point and two actuated points, each on the corner of an equilateral triangle.i will be getting a torque wrench next week to test, calculations so far have been based on the equations on the wikipedia leadscrew page.

author: Jimmy
author_rank: Regular Contributor
timestamp: February 18, 2011, 11:38:36 am
content: CoolAs i picture it in my head you have roughly 85kg with the center of mass roughly in center of triangle. One piviot point and 2 lead screws. You want to be able to accuratly position to the lead screws within a 10deg angle. Yeah but that motor is only rated at 0.0064 Nmlets look at thehttp://australia.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=4540861that motor is only rated at 0.0064 NmLets say we want Total peak torque including starting & stopping load = 5NmInput speed 11000 rpmOutput speed reqired is 3.6rpmgearbox 11000/4 = 3000:1There table shows us at maxumum efficency that you will never geton rs page - Higher efficiency than spur (can be above 90%)Lets say it is at %80Thats 0.0064 X 3000 X 0.80 = 15.6 NMm for $60 cool that will workYou could Buy a CNC kithttp://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&isrelated=1&item=280621796746&viewitem=and gear them down

author: williefleete
author_rank: Regular Contributor
timestamp: February 18, 2011, 11:57:25 am
content: i had some servos which had metal gears. i think it could supply about 13Kg of torque not sure what that would be in newtons they werent continuous rotation though. the torque on those ones would have been for plastic gears

author: sonicj
author_rank: Frequent Contributor
timestamp: February 18, 2011, 08:21:07 pm
content: cordless screwdriver

author: sonicj
author_rank: Frequent Contributor
timestamp: February 18, 2011, 08:34:23 pm
content: 12 VDC Gearhead DC Motor 13.6 RPM$19.9512V DC Gear Motor w/ Micro-Switch 10 Rpm$9.95DC Gearhead Motor - 12Vdc 4.5rpm$12.95and the list goes on...you can call or email them with your exact needs. chances are, they'll have it.