Worm Gears-worst efficiency

[Turn]

hey guys -

For anyone still at the design stage wondering what to buy for their motors I wanted to offer some friendly advice. Avoid worm gear types whenever possible. I realize they can simplify things greatly sometimes (motor+nice gear reduction in one compact unit), but they offer typically very low efficiency.

So, your 250W motor turns into a 100W motor instantly coupled to a typical 40% efficient worm gear transmission (20:1 reduction ratio). Only 50W @40:1. While worm gear efficiency varies greatly, all things being equal it's the worst way to go.

Usually you're better off rigging up a regular spur gear set or belt drive whose efficiencies are more in the 98% neighborhood. And cheaper by far. That increased efficiency will be felt with much quicker and more accurate motions in your rig. Or conversely, you can spend less on the motor for the same performance.

Thoughts?

[sirnoname]

Ok, then you have to explain where the 150W will be!
That power must change to heat somewhere.

[tronicgr]

Still, its better that the efficiency loss you will have in heat trying to hold a freewheeling motor in position under load. Not to mention that all that heat WILL be produced in the motor driver and generally it not good for the mosfet stages they use.

Thanos

[Turn]

Heat and noise.

Yes, trying to hold a tiny motor under load's not an option. There the worm-gear's braking effect is useful. However, it's a shame that, and its other benefits, come at such a high price. This is good to be aware of, so alternative actuator designs can, at least, be considered.

There's lots of ways to go about things. Roland van Roy's solutions are brilliant: http://simprojects.nl/diy_motion_platform_iv.htm

Where budget is a big factor, creativity and efficiencies are paramount, right? Worm gear...not the best for either.

[Mambo]

I would like to see this http://urobotics.urology.jhu.edu/projects/BW/ with my own eyes.

[dearn]

Yes, trying to hold a tiny motor under load's not an option. There the worm-gear's braking effect is useful. However, it's a shame that, and its other benefits, come at such a high price. This is good to be aware of, so alternative actuator designs can, at least, be considered.

I wouldn't see why thats is the reason to "avoid worm gear types whenever possible" next to the effeciency??

Just give the motor some big amp

[motiondave]

Agreed with Dearn. There are some very good motors out there..... http://www.motiondynamics.com.au/worm-d ... orque.html about 90% efficiency as noted by the supplier ( he told me this privately) and myself and Bobuilt will state how good these and other similar motors are, like the ebay bought daytons.

I have to ask you then Turn, have you actually tried any worm gear motors apart from wipers?

Where are you getting your information from?

[Turn]

That Motion Dynamics motor would be impressive, if its really what they say it is. Here's its posted specs from your link:

200W/16V max
170 RPM
20 Nm
14A max current at 16V loaded (says it can be overdriven a bit, but "not recommended")

Here's what math for the above gives: 170 RPM @ 20Nm = 356W at the crank. Now, assume 90% gear efficiency and 80% electric motor efficiency means the motor must consume 494W @ 16V in order to do what they claim. And do 31A. Do you think that 200W motor does 500W? I'm not trying to be a smart ass at all I'm honestly asking. I've spent quite a bit of time on eBay scrounging for motors and found nothing remotely, remotely close to this for $109.

Regarding worm efficiencies, those specs are in engineering texts and readily available charts.
http://www.roymech.co.uk/Useful_Tables/Drive/Gear_Efficiency.html
https://docs.google.com/viewer?a=v&q=cache:2qo38-OcplIJ:agriauto.bime.ntu.edu.tw/printed/ciam/ciam16/16-2/16-2-4.PDF+&hl=en&gl=ca&pid=bl&srcid=ADGEESglQx9tY4jSjU4H2W5g0odaAw2G4CwL5VQUHljSI7QcO6URpsAM0S0IG3DPEBP0Vv9RqArbUaJ33D7oNMnmgaVEa_EzJEjoy_Y34v6exFiLZA1UQCO6tz_YjIq70O--95rXp5t6&sig=AHIEtbSHt5zuX-kfceZCmyEYvwjGx3WDkw


Hey, do you have any other links to those Dayton DC motors? I'd appreciate it. Thanks.

[sirnoname]

Simple ask them or the developer.
We did this in the past and the motor developer (mostly local companies) did reply to that statements.

[motiondave]

Ok I may not have my information correct.
I know this with the motors, I have run them at 14 v and 38 amps stall current to give me some fierce motion, volts times amps equals watts 532 I think. They are fast, but require a lot of power to do so. Yes they are being WAAAAAAYYYY overdriven, but these motors and the daytons will handle it.

But lets examine something. A car drive line, you have an engine, gearbox and final drive. You loose efficiency of about 30% from engine to back/front axles.
Should you be saying to car manufacturers that they have got it all wrong?

There is going to be some loss of efficiency with a gearbox. The motion dynamics gearbox has been engineered to overcome most of this. Not sure how much.
You need a gearbox to get torque. Torque is what moves the weight you have put on it.
So if you want to move more weight, redesign or throw more power at it.

DIY motion simulators, especially for race , the motors change direction very quickly , and they will use power to do so, yes they heat up, that's what fans are for.
You are suggesting a belt or gear drive. Now as far as I can see, unless the gear or belt is VERY tight, you would not get the fine vibration of motion that usually comes with race or even some flight.
Thats where a worm gear comes in, it is a tight and solid fit.
Same with an actuator, a geared setup that can recreate fine motion, because of the very small tolerances in contact of mechanical components.
Small , fine mechanical tolerances. Not slack to over come.
And no Tronic, I am not having a dig at your joyrider with belt setups, just making a point

Next thing, simulator examples you posted.
http://simprojects.nl/diy_motion_platform_iv.htm Its a flight sim with sarius style linkages and chains. I guarantee they would not get the fine motion we crave if it was a race setup.
For flight, its good, for race....dunno...

ok, the other link http://www.roymech.co.uk/Useful_Tables/ ... iency.html
To put it bluntly, we are NOT trying to save power here, we are trying to recreate motion. If it means using "inefficient" motors with too much power, then we will do that.
I appreciate the advise and information posted, but to suggest something without examining it or even having designed, built and used motors and frames yourself is a bit rough. Unless of course you have done so

For cost reasons, if big worm gear motors are cheap but need lots of juice.....ummm.....so what then?
Actuators are more expensive, but would use less power probably, but they cost more.
Are we trying to save the planet over 100watts? Or are we trying to have some fun.