Need a "constant torque" slip clutch

Bodine calls them "torque motors," but they suffer the same size shortcoming as mag particle brakes. A 20 ft-lb torque motor would be enormous. When I was a kid I had a pair of torque motors I scavenged from a Univac 2 tape drive. They were about the size of a cast iron

Ned Simmons fired this volley in news: snipped-for-privacy@4ax.com:

But Ned, keep in mind that those motors were designed to produce that torque all the way up to several hundred RPMs.

Mine only needs 3+ RPM... so I multiply the motor torque with belting or sprocket drives.

LLoyd

Do you need the roving in constant tension when something is being done to it, or does it need to be spooled up at constant tension?

In the former case, it seems like you could have two drums set up with constant-torque motors or clutches. The roving would be stretched at constant tension between these fixed-diameter drums, wouldn't it? Might need idler rollers to pressed the roving against them.

A DC motor has torque proportional to the Current. The dancer arm could control the Current command to the motor, but with a fair amount of low pass Filtering so that it does not hunt. A DC motor and drive may well be cheaper, simpler and easier than mechanical brakes etc.

The split phase motor may not enjoy the constant stalled condition. The DC motor shouldn't care.

James Waldby fired this volley in news:hvgkkd$2oh$1 @news.eternal-september.org:

yep, that's one very proper way to do it, and if the real estate inside the (existing) machine would permit, I'd add a shaft with a "windlass drum" running at constant torque. No room, though.

LLoyd

Cross-Slide fired this volley in news:a806363e- snipped-for-privacy@i28g2000yqa.googlegroups.com:

Primarily, it would not enjoy it because they're (gear motors) usually fan cooled, and the fan wouldn't be running during stall.

But I forgot something important, anyway. Split phase motors don't mind being stalled OR operating at reduced voltages, but they don't develop much starting torque below a certain saturation voltage. Only a "bang- bang" control would work with a typical split-phase type motor.

A DC motor would be perfect -- don't have one that fits my gear reducer, but I can get one. A 3-phase motor would be OK too, with the dancer driving the frequency pot of a VFC.

LLoyd

What's that Lassie? You say that Lloyd E. Sponenburgh fell down the old rec.crafts.metalworking mine and will die if we don't mount a rescue by Fri, 18 Jun 2010 12:21:55 -0500:

Could you find one that would produce 10ft-lb at 10 rpm, and gear it down

Or one at 5ft.-lb at 20rpm? Or one at 2.5ft-lb at 40rpm? Etc.

snipped-for-privacy@privacy.net (dan) fired this volley in news:4c1eede3.3077001 @news20.forteinc.com:

Yep... probably. Already dealt with multiplying the torque via belting or chain drive in another post.

LLoyd

horse power = torque (ft lbs) * speed (rpm) / 5240

The motors probably wouldn't last long but the education would be quick and cheap.

Hul

snipped-for-privacy@kbrx.com fired this volley in news:hvgtvh$9fj$ snipped-for-privacy@reader1.panix.com:

ACtually... I have a couple of Ampex tape spool motors rated at 30VDC 6.5A.

It'll take some time in the machine shop to adapt them (they won't take the overhung weight necessary on the main belting run) not because of the fundamental difficulty of doing it, but because of real estate limitations in the machine.

LLoyd

The torque of a DC permanent magnet (DCPM) motor is proportional to current regardless of speed. The motor won't overheat as long as it's operated within its max current rating, even if stalled.

If you could rig up a 10:1 speed reducer with timing belts and pulleys (zero backlash) then your torque requirement would be 2 lbf*ft at about 50 RPM. A DC motor capable of delivering 2 lbf*ft at 2000 RPM (a more usful speed for motors in general) would be a 90 watt (0.121 HP) motor. I don't think that'd be hard to find on the surplus market. Or, you could go with a DCPM gear, e.g. power seat motors, power window motors, windshield wiper motors, etc. Some windshield wiper motors run at about 50 RPM. 20 ft-lbf at 50 RPM is about 23 watts, which is not quite 2 amps at 12 volts. Wiper motors are rated for more like 5 amps.

Not all DC motors in automobiles are PM motors, though. Some are series-wound. They'd work, but they're a bit trickier to control because their torque is not linearly proportional to current.

Another possibility might be an inexpensive cordless drill operated from a current regulator. Even a modest drill can deliver 200 in-lbf which is 22.5 ft-lbf, and it can do that at low to stall speeds all day.