It is currently Sat Nov 28, 2020 10:56 am




Post new topic Reply to topic  [ 5 posts ] 
 Increasing torque with traditional linear motion (ballscrew) 
Author Message
User avatar

Joined: Wed May 27, 2009 5:10 pm
Posts: 56
Post Increasing torque with traditional linear motion (ballscrew)
Hi,

As some of you probably know, I have an impossible project... I need to move around 60 pounds vertically with the lowest budget possibly... Mainly for timelapse tracking shots, but ideally I'd also want to run this "moco" rig with highish speeds (realtime video work).

I calculated some torque requirements for belt+pulley omega-style drive and they are huge! I'd need around 300 Nm's (around 2660 pounds/inches) of torque to drive that 60 pound payload vertically?

So it would either mean a very huge pulley to get long enough lever, or gearing the motor a lot. Does this sound right at all? I've rounded the numbers quite a bit. Of course it would be possible with a beefy motor and something like a 150:1 planar gearbox. But then the high-speed option would be out... I'm a bit skeptical of my math, can't really believe I'd need that much torque.

Then I poked around with this calculator: http://www.racointernational.com/screw_formula.htm

Is that correct? With a ballscrew I'd need only less than 3Nm's of torque to do the same thing? Of course the speed wouldn't be comparable at all, but at least I could move that payload vertically. I guess I'd need some kind of external brake, since finding a stepper with enough holding torque for that kind of payload would probably be a "challenge". My maximum speed would take a serious hit, so running at high speeds wouldn't be possible with a ballscrew drive.

I guess I'll have to start researching counter-balanced systems ;-)

_________________
Riku Naskali
http://www.stereowindow.us
http://www.youtube.com/user/stereowindow


Sun Mar 06, 2011 6:43 pm
Profile
User avatar

Joined: Wed May 27, 2009 5:10 pm
Posts: 56
Post Re: Increasing torque with traditional linear motion (ballscrew)
Well, I guess the math was wrong. Thank god. Does this seem right?

100 Ncm = 1Nm. (~ 10kg 1cm from the rotation point OR 1kg 1m from the rotation point)

Which would enable me to use, say, a 650 Ncm stepper with a 2 cm radius of pulley (increasing the torque to 1300Ncm?).

Sorry about the metrics, way too many units involved in this :-)

_________________
Riku Naskali
http://www.stereowindow.us
http://www.youtube.com/user/stereowindow


Mon Mar 07, 2011 1:41 am
Profile
Post Re: Increasing torque with traditional linear motion (ballscrew)
Well, hate to burst your bubble - but a good ballscrew and anti-backlash nut are, well, not very cheap =)

Especially trying to hit that load rating, consider coupling the motor to that ballscrew as well and the price of a high-torque anti-backlash coupler, then of course, precision bearings for both ends of the screw, machining down the ends of the screw...

Hi speed and ballscrews don't play well together, unless you're moving under 12" or so, you're going to to get whip at high speeds, and the vibration is going to be a killer. Generally, the way to get high speeds out of a ballscrew is to leave the ballscrew fixed and have the anti-backlash nut be the drive (i.e. moving part) to prevent whip - otherwise, you have to go overkill on the ballscrew to eliminate the whip, and end up with a very inefficient drive.

Have you considered rack and pinion? It's the best of both worlds between the ballscrew and belt-driven designs. High speed with no whip, and no worries about the stretch factor on the belt. Stabilize your load using parallel shafts w/ linear bearings, and then a rack-and-pinion drive handles the vertical motion.

!c


Tue Mar 15, 2011 4:50 pm
User avatar

Joined: Tue Aug 26, 2008 3:30 am
Posts: 824
Location: Sydney, Australia
Post Re: Increasing torque with traditional linear motion (ballscrew)
Have to agree with Shutterdrone on the price point of an effective ball screw solution.
I've seen one used on a moco crane that was sourced from the mechanisms that raise and lower flaps(?) on commercial aircraft. Not cheap.


Tue Mar 15, 2011 5:20 pm
Profile
User avatar

Joined: Wed May 27, 2009 5:10 pm
Posts: 56
Post Re: Increasing torque with traditional linear motion (ballscrew)
There are chinese ballscrews with ballnuts, complete mounting blocks & end-machining for around $200 on ebay (for over 1.2 meters).

However I largely discarded this idea, since I don't think there is any need to use a screw-drive (and I learned about screw-whip).

Can someone verify my latest calculations are correct? That would mean I could easily hit my intended speed and torque goals with a beefy Nema34 stepper using a 3" diameter pulley in omega-drive.

_________________
Riku Naskali
http://www.stereowindow.us
http://www.youtube.com/user/stereowindow


Sat Mar 19, 2011 9:47 am
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 5 posts ] 


Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB © phpBB Group.
Designed by Vjacheslav Trushkin for Free Forums/DivisionCore. pozycjonowanie