Last days i have been thinking of this wire suspended lineair arm construction. Not offending, and don't want to "bomb" all ideas here. But i think it will not work, it will give too much resistance imo.
Example: have you ever seen a bicycle with a belt drive system? Because the friction gets too high then, problably not. It would be a nice training bike to enhance muscles, but not a general purpose bike.
A V-shaped wheel gives resistance on the wire, just like a V-belt. Especially when the tension on the wire increases in the lineair arm design.
The good old hard steel roller chain works better here to drive the bike, has lesser rolling resistance. It has only small hard contact points with rollers.
Example: have you ever seen a bicycle with a belt drive system? Because the friction gets too high then, problably not. It would be a nice training bike to enhance muscles, but not a general purpose bike.
A V-shaped wheel gives resistance on the wire, just like a V-belt. Especially when the tension on the wire increases in the lineair arm design.
The good old hard steel roller chain works better here to drive the bike, has lesser rolling resistance. It has only small hard contact points with rollers.
I guess I agree with this, though of course the wire idea may work. Still, I'm trying a design that uses 4 small ball bearings riding on a metal rod. I got some tiny bearings that are used in dental handpieces. I'm going to use a rod about 6mm diameter, because I already have one.
Does anyone know a good diy method for measuring the side force required to get the arm moving? If we could devise such a thing, it would be a good way to compare notes.
Tubee ,
The major component of friction will be the actual bearing @ the
centre of the diabolo shaped rollers ,which is why i advocate using small dia .spindles in PTFE rollers. The friction between the wire and the rollers is necessary or they wouldnt roll at all and you might as well use sliders .Your chain analogly is actually closer than you might think
at the macroscopic, level the 4 tiny contact points on the rollers are the equivalent of the chainwheel teeth running along an unwound chain
( the wire). This is in fact no different to the outer race of the roller bearing running in the glass tube.
The major component of friction will be the actual bearing @ the
centre of the diabolo shaped rollers ,which is why i advocate using small dia .spindles in PTFE rollers. The friction between the wire and the rollers is necessary or they wouldnt roll at all and you might as well use sliders .Your chain analogly is actually closer than you might think
at the macroscopic, level the 4 tiny contact points on the rollers are the equivalent of the chainwheel teeth running along an unwound chain
( the wire). This is in fact no different to the outer race of the roller bearing running in the glass tube.
Pixpop ,
One of my other zany ideas when chewing over this problem was to apply a side load similar to a bias compensation idea in reverse, so to speak, equivalent to the friction in the bearings .This would work if
records were perfect ,but there not so it was discounted BUT you could run a cord over a couple of pulleys to determine the static force required to initiate movement.
One of my other zany ideas when chewing over this problem was to apply a side load similar to a bias compensation idea in reverse, so to speak, equivalent to the friction in the bearings .This would work if
records were perfect ,but there not so it was discounted BUT you could run a cord over a couple of pulleys to determine the static force required to initiate movement.
?????
"Example: have you ever seen a bicycle with a belt drive system? Because the friction gets too high then, problably not. It would be a nice training bike to enhance muscles, but not a general purpose bike"
?????
Excuse me but Peugeot certainly made bikes with belt drive system that were very confortable to drive and were much quieter that the chain system.
I owned one in the late 80' .... Took no maintenance and the fact sheet showed that a belt was much stronger than a chain...
jean-Pierre
"Example: have you ever seen a bicycle with a belt drive system? Because the friction gets too high then, problably not. It would be a nice training bike to enhance muscles, but not a general purpose bike"
?????
Excuse me but Peugeot certainly made bikes with belt drive system that were very confortable to drive and were much quieter that the chain system.
I owned one in the late 80' .... Took no maintenance and the fact sheet showed that a belt was much stronger than a chain...
jean-Pierre
i second uvodee. I think the analoge is irrelevant not to mention false.
Here is my plan:
I am gonna have a pyrex rod spun by an electric motor. maybe at 200rpm. something like that. I might use the motor to provide downforce. anyway, on the rod will ride a carriage machined from a slippery plastic. The holes through which the rod will spin will be only very slightly larger than the rod but large enough to not impede its spinning. I may grease this as well, but not so much as to increase the friction. I believe that this semi solid foundation will provide good damping in both directions with much more in the tangential direction. Also, I should be able to control the damping vie the motor speed.
Here is my plan:
I am gonna have a pyrex rod spun by an electric motor. maybe at 200rpm. something like that. I might use the motor to provide downforce. anyway, on the rod will ride a carriage machined from a slippery plastic. The holes through which the rod will spin will be only very slightly larger than the rod but large enough to not impede its spinning. I may grease this as well, but not so much as to increase the friction. I believe that this semi solid foundation will provide good damping in both directions with much more in the tangential direction. Also, I should be able to control the damping vie the motor speed.
tade,
I was thinking sort of on the same line.
Picture this:
Instead of an air track, have a shaft of precision ground steel, spinning such that its top edge is rotating away from the record's surface.
The tonearm rides on the shaft on two precision cartridge bearings, one in front of the other, like a bicycle riding around a barrel. The bearings' axis of rotation is parralell to that of the shaft.
In this orientation, the shaft must be rotating for the tonearm to traverse it. As the tonearm gets pulled by the stylus in the groove, it tweaks the arm at a slight angle. This causes the bearings to ride the shaft slightly crooked, forcing them to "thread" along the shaft until they resume parallel rotation. It's sort of a self-correcting mechanical servo system.
Sorry, no pictures.
There's probably a few issues to deal with like requiring a low slung counter-weight to keep azimuth balanced, figuring out what profile of "tire" to put on the bearings, keeping bearing rumble to a minimum...
Max
I was thinking sort of on the same line.
Picture this:
Instead of an air track, have a shaft of precision ground steel, spinning such that its top edge is rotating away from the record's surface.
The tonearm rides on the shaft on two precision cartridge bearings, one in front of the other, like a bicycle riding around a barrel. The bearings' axis of rotation is parralell to that of the shaft.
In this orientation, the shaft must be rotating for the tonearm to traverse it. As the tonearm gets pulled by the stylus in the groove, it tweaks the arm at a slight angle. This causes the bearings to ride the shaft slightly crooked, forcing them to "thread" along the shaft until they resume parallel rotation. It's sort of a self-correcting mechanical servo system.
Sorry, no pictures.
There's probably a few issues to deal with like requiring a low slung counter-weight to keep azimuth balanced, figuring out what profile of "tire" to put on the bearings, keeping bearing rumble to a minimum...
Max
Nice discussing here, thats what this forum is for!
Pixpop: we could a make a glass tube/ball bearing lineair arm, and a wire suspended arm, and load it with a simple but well known cartridge, e.g cheap Ortofon OMB 5 to test with. (But this cart has relatively soft suspended cantilever) Then look how far the cantilever is tilting until the carriage starts to move.
An other option: measure the rolling resistance (the force when the carriage starts to roll) with a precision weight tool. I have here a Haag-Streit Correx, but with smaller read-out, until 6 gramms. Like this but has flat tip: http://www.longislandindicator.com/Resources/correx301.gif
Pixpop: we could a make a glass tube/ball bearing lineair arm, and a wire suspended arm, and load it with a simple but well known cartridge, e.g cheap Ortofon OMB 5 to test with. (But this cart has relatively soft suspended cantilever) Then look how far the cantilever is tilting until the carriage starts to move.
An other option: measure the rolling resistance (the force when the carriage starts to roll) with a precision weight tool. I have here a Haag-Streit Correx, but with smaller read-out, until 6 gramms. Like this but has flat tip: http://www.longislandindicator.com/Resources/correx301.gif
I have been looking in my ball-bearing drawer. Found 2 suitable bearings, outer dia 7.5 mm, axle dia. 3.2 mm (1/8 inch) and with a flange on it, so it will have 2 small contact points on the glass. The flange is on one side, not in the middle, but for an experiment it will do. 1/8 inch axle, so it must be the tape drive i demolisched +/- a year ago, came out of brass/rubber capstan roller. Grease hardened, but in washed it away with petrol, now they roll very light.
Now i have to find a laboratory glass supllier, to find a suitable Pyrex or AR glass tube, will check for smooth surface inside. (could have grooves in it from extruding-process in glass factory?)
I rubbed the flange of ballb. over a hard steel polished axle: again allmost no resistance.
Now i have to find a laboratory glass supllier, to find a suitable Pyrex or AR glass tube, will check for smooth surface inside. (could have grooves in it from extruding-process in glass factory?)
I rubbed the flange of ballb. over a hard steel polished axle: again allmost no resistance.
Just a thought :-
How many balls are in a ball bearing and is the rolling resistance
of all these balls on the inner and outer tracks + the rolling resistance of the outer race on the glass/wire less than plain PTFE rollers ?
The spinning rods would work for reducing friction but I think the
contact point should be a knife edge which implies at least 2 sets to maintain cartridge alignment.I think it would be asking a lot for a cartridge to tilt the flat bearing enough for it to thread its way along the rod.
How many balls are in a ball bearing and is the rolling resistance
of all these balls on the inner and outer tracks + the rolling resistance of the outer race on the glass/wire less than plain PTFE rollers ?
The spinning rods would work for reducing friction but I think the
contact point should be a knife edge which implies at least 2 sets to maintain cartridge alignment.I think it would be asking a lot for a cartridge to tilt the flat bearing enough for it to thread its way along the rod.
baggins said:
By 2 sets, do you mean 4 bearings? I was thinking a pair of bearings, one in front of the other, like a bicycle. The bearings would have rounded tires on them, making for a pair of near point contact patches and should be easily manoeuvred.
The pitch of the virtual thread would be determined by the deflection of the tonearm. The greater its angle, the coarser the pitch and the quicker it will traverse the shaft to correct for the error. As the arm approaches the perpendicular, its pitch reduces and its rate of speed along the shaft slows (to zero at the perpendicular).
Max
Hi,
Yes i think that if you place the bearings @ right angles to the spinning rod you need 4 of them with knife edge contacts or the cartridge can rotate about the axis of the arm .If you use the width of the bearing outer race to cope with this problem I think the friction
will be to high ( this is only my opinion though) I have no way --apart from the obvious-- to substantiate my view!
Yes i think that if you place the bearings @ right angles to the spinning rod you need 4 of them with knife edge contacts or the cartridge can rotate about the axis of the arm .If you use the width of the bearing outer race to cope with this problem I think the friction
will be to high ( this is only my opinion though) I have no way --apart from the obvious-- to substantiate my view!
progress...
I spent some time this weekend putting together a passive linear tracker based on some ideas from this thread. It all went together pretty easily, and in general I'm very encouraged. I hope other folks will go ahead with their versions and share the results.
Overall view: The armtube is aluminum, 4.75mm dia. The rail is a brass rod, about 5mm dia, exactly as it came from the hardware store.
The carriage assembly, and counterweight. Signal wires currently held in place with sticky tape.
Carriage assembly detail. The bearings are ABEC 7 bearings, for dental drills. They are screwed into a small length of 1/4 inch square brass extrusion. The inverted V is made from the same material. The brass pieces are soldered together, and attached to the armtube with epoxy. Since my screws were too long, I had to offset the bearings on one side so the screws wouldn't interfere. There's about 2mm clearance between the bottom of the brass rod, and the top of the armtube. The small square section with the bearings mounted weighed about 6 grams before being soldered in place.
The business end: I cut a small piece of copper clad board and drilled two holes 1/2" apart to mount the cartridge. The copper clad board is epoxied to the end of the armtube. The wires and clips were salvaged from some cheesy turntable. None of the metal is grounded, and there's no hum. The ground sides of the cartridge wires are grounded at the phono preamp. This is my junk cartridge, not ready to mount my good one yet. I removed the stylus while taking the pictures.
The counterweight: I epoxied a small iron bar to the end of the armtube. Then I stuck a magnet to it, and added ball bearings enough to balance the cartridge. Next time, I think I would just epoxy the magnet to the armtube, and use bigger ball bearings to make up the weight.
The red and white boxes are 35mm slide boxes as temporary stpports. The rod is stuck to them with masking tape. The blue thing behind the arm, and the red thing in the top right corner, are milled aluminum lens mounts that I'm using to hold things in place.
And the result? Surprisingly good. It worked immediately. No tracking problems. It maintains contact on a warped record, and doesn't skip or stick anywhere. The arm seems to move smoothly throught the LP side, even though my brass rod is a little rough.
The problems:
* Bass is somewhat lean. Not surprising really, given the lack of rigidity in the mounting of the rod. I'm not sure how much of this is due to my junk cartridge. If I get brave, I'll mount my good one for comparison.
* The whole thing is very fiddly. It would be good to come up with some kind of horizontal damping so it doesn't go flying at the drop of a hat.
* The rod is too thin, and vibrates too easily. There's a vicious resonance at about 40 Hz that goes away if you press on the rod. You can actually feel the rod vibrating when you do this. I think it should be maybe 10mm thick, and supported at only one end. This would allow it to be shorter, which would make the whole thing more manageable.
* I made the carriage assembly too short. This causes it to lose contact too easily when cueing. Don't know if this happens during play. I angled the bearings at 45 degrees. I'd like to experiment with making their axes a little more vertical, as long as they don't jam.
* I'd like to use carbon fibre instead of aluminum for the arm tube. Alternatively, I could use brass, as it can be soldered. The soldered joints just feel better than the epoxied ones.
* The rod should be made of harder material. Next time, I'll use a hardened steel rod.
I spent some time this weekend putting together a passive linear tracker based on some ideas from this thread. It all went together pretty easily, and in general I'm very encouraged. I hope other folks will go ahead with their versions and share the results.
Overall view: The armtube is aluminum, 4.75mm dia. The rail is a brass rod, about 5mm dia, exactly as it came from the hardware store.
An externally hosted image should be here but it was not working when we last tested it.
The carriage assembly, and counterweight. Signal wires currently held in place with sticky tape.
An externally hosted image should be here but it was not working when we last tested it.
Carriage assembly detail. The bearings are ABEC 7 bearings, for dental drills. They are screwed into a small length of 1/4 inch square brass extrusion. The inverted V is made from the same material. The brass pieces are soldered together, and attached to the armtube with epoxy. Since my screws were too long, I had to offset the bearings on one side so the screws wouldn't interfere. There's about 2mm clearance between the bottom of the brass rod, and the top of the armtube. The small square section with the bearings mounted weighed about 6 grams before being soldered in place.
An externally hosted image should be here but it was not working when we last tested it.
The business end: I cut a small piece of copper clad board and drilled two holes 1/2" apart to mount the cartridge. The copper clad board is epoxied to the end of the armtube. The wires and clips were salvaged from some cheesy turntable. None of the metal is grounded, and there's no hum. The ground sides of the cartridge wires are grounded at the phono preamp. This is my junk cartridge, not ready to mount my good one yet. I removed the stylus while taking the pictures.
An externally hosted image should be here but it was not working when we last tested it.
The counterweight: I epoxied a small iron bar to the end of the armtube. Then I stuck a magnet to it, and added ball bearings enough to balance the cartridge. Next time, I think I would just epoxy the magnet to the armtube, and use bigger ball bearings to make up the weight.
An externally hosted image should be here but it was not working when we last tested it.
The red and white boxes are 35mm slide boxes as temporary stpports. The rod is stuck to them with masking tape. The blue thing behind the arm, and the red thing in the top right corner, are milled aluminum lens mounts that I'm using to hold things in place.
An externally hosted image should be here but it was not working when we last tested it.
And the result? Surprisingly good. It worked immediately. No tracking problems. It maintains contact on a warped record, and doesn't skip or stick anywhere. The arm seems to move smoothly throught the LP side, even though my brass rod is a little rough.
The problems:
* Bass is somewhat lean. Not surprising really, given the lack of rigidity in the mounting of the rod. I'm not sure how much of this is due to my junk cartridge. If I get brave, I'll mount my good one for comparison.
* The whole thing is very fiddly. It would be good to come up with some kind of horizontal damping so it doesn't go flying at the drop of a hat.
* The rod is too thin, and vibrates too easily. There's a vicious resonance at about 40 Hz that goes away if you press on the rod. You can actually feel the rod vibrating when you do this. I think it should be maybe 10mm thick, and supported at only one end. This would allow it to be shorter, which would make the whole thing more manageable.
* I made the carriage assembly too short. This causes it to lose contact too easily when cueing. Don't know if this happens during play. I angled the bearings at 45 degrees. I'd like to experiment with making their axes a little more vertical, as long as they don't jam.
* I'd like to use carbon fibre instead of aluminum for the arm tube. Alternatively, I could use brass, as it can be soldered. The soldered joints just feel better than the epoxied ones.
* The rod should be made of harder material. Next time, I'll use a hardened steel rod.
A suitable hardened steel precision ground rod is freely available in Scanners - its the guide rails for the scanning carriage (you may get lucky with an old inkjet printer too 
).
To stop the carriage going flying - how about a magnet directly above the rail - a little induction goes a long way
Owen
).To stop the carriage going flying - how about a magnet directly above the rail - a little induction goes a long way
Owen
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