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#1
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rpm
Hi,
Perhaps someone might be of help? I am building a my own router table that will have a 3HP router motor rated at 23,000 rpm. I have a speed controller that will vary the motor speed but of course there is no actual speed readout. Depending upon the diameter of the bits one must lower or raise the speed of the motor. My desire is to build a sensor and display that would read out the rpm. I am good with a soldering iron and in the past have built a few FM radio, and other kits. Perhaps someone could point me in the direction of a kit that might do the job or perhaps find a schematic that I could build. I was thinking that the sensor would be some kind of light sensor that would 'see' a white line painted on the chuck of the router? I searched the newsgroup for 'rpm' or 'speed' and came up blank. I also searched google with mixed results. Any help would be greatly appreciated! fritz |
#2
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rpm
Building a tachometer with readout is a bit of a challanging task
Why not use a laser strobe tackometer: See Pocket Tach 99 (PT99) for $150 http://www.monarchinstrument.com/Poc...ser.htm#Pocket Thats probably cheaper - and much much quicker than you can buy the parts and build one Dan -- Dan Hollands 1120 S Creek Dr Webster NY 14580 585-872-2606 www.QuickScoreRace.com "fritz" wrote in message ... Hi, Perhaps someone might be of help? I am building a my own router table that will have a 3HP router motor rated at 23,000 rpm. I have a speed controller that will vary the motor speed but of course there is no actual speed readout. Depending upon the diameter of the bits one must lower or raise the speed of the motor. My desire is to build a sensor and display that would read out the rpm. I am good with a soldering iron and in the past have built a few FM radio, and other kits. Perhaps someone could point me in the direction of a kit that might do the job or perhaps find a schematic that I could build. I was thinking that the sensor would be some kind of light sensor that would 'see' a white line painted on the chuck of the router? I searched the newsgroup for 'rpm' or 'speed' and came up blank. I also searched google with mixed results. Any help would be greatly appreciated! fritz |
#3
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rpm
On 2005-12-21, fritz wrote:
Hi, Perhaps someone might be of help? I am building a my own router table that will have a 3HP router motor rated at 23,000 rpm. I have a speed controller that will vary the motor speed but of course there is no actual speed readout. Depending upon the diameter of the bits one must lower or raise the speed of the motor. My desire is to build a sensor and display that would read out the rpm. I am good with a soldering iron and in the past have built a few FM radio, and other kits. Perhaps someone could point me in the direction of a kit that might do the job or perhaps find a schematic that I could build. I was thinking that the sensor would be some kind of light sensor that would 'see' a white line painted on the chuck of the router? I searched the newsgroup for 'rpm' or 'speed' and came up blank. I also searched google with mixed results. Any help would be greatly appreciated! and RPM measuring device is called a "tachometer". a sdimilar device called a "frequency counter" will give you a result exactly 60 times lower. there are off-the-shelf and kit versions of both. good luck. PS. There may be a tachometer for motorcycle applications that can read upto 23000. as for the sensor, a line on the shaft, or some sort of magnetic sensor ... Bye. Jasen |
#4
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rpm
Dan Hollands wrote:
Building a tachometer with readout is a bit of a challanging task Why not use a laser strobe tackometer: See Pocket Tach 99 (PT99) for $150 http://www.monarchinstrument.com/Poc...ser.htm#Pocket Thats probably cheaper - and much much quicker than you can buy the parts and build one Dan Dan, Thanks for the info. Unfortunately the space available is very limited and is under the top which would negate the reading of the display. I looked at the pocket tach and it wouldn't do the job. But thanks any. f. |
#5
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rpm
Jasen Betts wrote:
and RPM measuring device is called a "tachometer". a sdimilar device called a "frequency counter" will give you a result exactly 60 times lower. there are off-the-shelf and kit versions of both. good luck. PS. There may be a tachometer for motorcycle applications that can read upto 23000. as for the sensor, a line on the shaft, or some sort of magnetic sensor ... Bye. Jasen Jasen, Thanks for the info! I will look into both of the things you suggest. If anything works out I will put it back here at the newsgroup. f. |
#6
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rpm
----------------------------
"fritz" wrote in message ... Hi, Perhaps someone might be of help? I am building a my own router table that will have a 3HP router motor rated at 23,000 rpm. I have a speed controller that will vary the motor speed but of course there is no actual speed readout. Depending upon the diameter of the bits one must lower or raise the speed of the motor. My desire is to build a sensor and display that would read out the rpm. I am good with a soldering iron and in the past have built a few FM radio, and other kits. Perhaps someone could point me in the direction of a kit that might do the job or perhaps find a schematic that I could build. I was thinking that the sensor would be some kind of light sensor that would 'see' a white line painted on the chuck of the router? I searched the newsgroup for 'rpm' or 'speed' and came up blank. I also searched google with mixed results. Any help would be greatly appreciated! --------- A white line and a photocell can be made to work at 1 pulse/revolution- feed it into a counter. Add more lines for more counts/ per rev. A lamp shining through a film circle with alternating black and clear areas (i.e. a negative) and a photocell will work (1 transistor amp may be needed). The number of areas can be adjusted to give multiple pulses per revolution but at the speed and needed accuracy, this won't be needed. Alternatively, glue a small magnet on the shaft and pick up magnetic pulses. I have done this at lower speeds- a disk giving 60 pulses/revolution, on a 1 second gate will give a 1 second count good to +/- 1 rpm. Select the number of pulses to give a convenient scale factor. (at 24000 rpm, 6 pulses per revolution give a count of 2400Hz -scale by 10 and you have your speed measurement to a satisfactory accuracy. HP also made a pulse tachometer - may be still available and price? -- Don Kelly @shawcross.ca remove the X to answer fritz |
#7
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rpm
Don Kelly wrote:
--------- A white line and a photocell can be made to work at 1 pulse/revolution- feed it into a counter. Add more lines for more counts/ per rev. A lamp shining through a film circle with alternating black and clear areas (i.e. a negative) and a photocell will work (1 transistor amp may be needed). The number of areas can be adjusted to give multiple pulses per revolution but at the speed and needed accuracy, this won't be needed. Alternatively, glue a small magnet on the shaft and pick up magnetic pulses. So I assume that if the line is reflective enough, the light source could be right beside the photocell. The distance between the photocell and the line would be about 1.3 inches but that could be ameliorated by encasing the photocell in a small tube with a focus on the line. A magnet wouldn't work because one has to use a wrench on the collet to remove the bit. I have done this at lower speeds- a disk giving 60 pulses/revolution, on a 1 second gate will give a 1 second count good to +/- 1 rpm. Select the number of pulses to give a convenient scale factor. (at 24000 rpm, 6 pulses per revolution give a count of 2400Hz -scale by 10 and you have your speed measurement to a satisfactory accuracy. HP also made a pulse tachometer - may be still available and price? I would use one or two lines so that should be well within the ability of a photocell to capture. Thanks for the verification that it can be done. I'll start looking at photocells after the holidays. Later I may need some help in getting from the photocell output and the counter out to the display. Thanks again for the input. f. |
#8
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rpm
On 2005-12-23, fritz wrote:
Don Kelly wrote: --------- A white line and a photocell can be made to work at 1 pulse/revolution- feed it into a counter. Add more lines for more counts/ per rev. A lamp shining through a film circle with alternating black and clear areas (i.e. a negative) and a photocell will work (1 transistor amp may be needed). The number of areas can be adjusted to give multiple pulses per revolution but at the speed and needed accuracy, this won't be needed. Alternatively, glue a small magnet on the shaft and pick up magnetic pulses. So I assume that if the line is reflective enough, the light source could be right beside the photocell. The distance between the photocell and the line would be about 1.3 inches but that could be ameliorated by encasing the photocell in a small tube with a focus on the line. A magnet wouldn't work because one has to use a wrench on the collet to remove the bit. if the shaft is shaped to accept a wrench it's be perfect for a variable reluctance pickup... it could be positioned behind the shaft where it doesn't get in the way of the wrench ______ / _____) _ ______/ //~~~\ |o| wrench //shaft\|~|~|~|___ sensor ______ \\ /|_|_|_| \ \\___/ |o| mounting \ ~~~~~) ~ ----- bracket ~~~~~~ shown with a hexagonal shaft but it'll work with round a shaft with two flat sides or with one or more notches etc too, it'll just give a different number of pulses per rotation. "reluctors" are used in electronic speedometer pickups etc once can probably be had for little cost from an automotive wrecker I had a car that had one on that sensed the flywheel's (ring gear) teeth it was only connected to the diagnotic socket. Bye. Jasen |
#9
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rpm
Jasen Betts wrote:
On 2005-12-23, fritz wrote: Don Kelly wrote: --------- A white line and a photocell can be made to work at 1 pulse/revolution- feed it into a counter. Add more lines for more counts/ per rev. A lamp shining through a film circle with alternating black and clear areas (i.e. a negative) and a photocell will work (1 transistor amp may be needed). The number of areas can be adjusted to give multiple pulses per revolution but at the speed and needed accuracy, this won't be needed. Alternatively, glue a small magnet on the shaft and pick up magnetic pulses. So I assume that if the line is reflective enough, the light source could be right beside the photocell. The distance between the photocell and the line would be about 1.3 inches but that could be ameliorated by encasing the photocell in a small tube with a focus on the line. A magnet wouldn't work because one has to use a wrench on the collet to remove the bit. if the shaft is shaped to accept a wrench it's be perfect for a variable reluctance pickup... it could be positioned behind the shaft where it doesn't get in the way of the wrench ______ / _____) _ ______/ //~~~\ |o| wrench //shaft\|~|~|~|___ sensor ______ \\ /|_|_|_| \ \\___/ |o| mounting \ ~~~~~) ~ ----- bracket ~~~~~~ shown with a hexagonal shaft but it'll work with round a shaft with two flat sides or with one or more notches etc too, it'll just give a different number of pulses per rotation. "reluctors" are used in electronic speedometer pickups etc once can probably be had for little cost from an automotive wrecker I had a car that had one on that sensed the flywheel's (ring gear) teeth it was only connected to the diagnotic socket. Bye. Jasen What an idea! I assume that it senses more or less metal within it's sensing range. The way the collet is shaped would give 4 pulses/rotation or 1600 pps. I assume that since it can sense all the teeth on a ring gear it ought to be able to do this. Thanks for the suggestion! f. |
#10
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rpm
______ / _____) _ ______/ //~~~\ |o| wrench //shaft\|~|~|~|___ sensor ______ \\ /|_|_|_| \ \\___/ |o| mounting \ ~~~~~) ~ ----- bracket ~~~~~~ What an idea! I assume that it senses more or less metal within it's sensing range. The way the collet is shaped would give 4 pulses/rotation or 1600 pps. I assume that since it can sense all the teeth on a ring gear it ought to be able to do this. Thanks for the suggestion! I've got bad news, it might not work - the magnetic field from the motor might be stronger than the differences caused by the shaft aproaching and retreating.. I just remembered similar sensors are also used in antiskid breaking systems ... but If it works it'll be immune to sawdust and the like.... Bye. Jasen |
#11
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rpm
Jasen Betts wrote:
I've got bad news, it might not work - the magnetic field from the motor might be stronger than the differences caused by the shaft aproaching and retreating.. I just remembered similar sensors are also used in antiskid breaking systems ... but If it works it'll be immune to sawdust and the like.... Bye. Jasen Well, I'll just start with a photocell and see how it goes. If that doesn't pan out I'll try this. Thank you! f. |
#12
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rpm
"fritz" wrote in message
... Jasen Betts wrote: I've got bad news, it might not work - the magnetic field from the motor might be stronger than the differences caused by the shaft aproaching and retreating.. I just remembered similar sensors are also used in antiskid breaking systems ... but If it works it'll be immune to sawdust and the like.... Bye. Jasen Well, I'll just start with a photocell and see how it goes. If that doesn't pan out I'll try this. Thank you! f. ---------- How much space do you have? This can limit options. The machines that I used a photocell on were 5HP units and space, away from couplings, wasn't a problem. There a negative of a picture of a circle with black and white sectors and about 6 inch diameter worked well. the light source and photocell were mounted in a U bracket over the film which was put between two sheets of 2mm plexiglass. Alignment as needed for a reflected signal wasn't critical as one was picking up the direct beam through clear areas on the film. It was necessary to amplify the output signal but the technology has advanced since then (early 80's) so better light output/sensing may not need the amplifier. It is no big deal to add one. The magnetic approach may still work but may need some shielding. Tin can around all but the pickup side. Even a shaft bump and a capacitive pickup can work. -- Don Kelly @shawcross.ca remove the X to answer ---------------------------- |
#13
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rpm
Don Kelly wrote:
--- How much space do you have? This can limit options. The machines that I used a photocell on were 5HP units and space, away from couplings, wasn't a problem. There a negative of a picture of a circle with black and white sectors and about 6 inch diameter worked well. the light source and photocell were mounted in a U bracket over the film which was put between two sheets of 2mm plexiglass. Alignment as needed for a reflected signal wasn't critical as one was picking up the direct beam through clear areas on the film. It was necessary to amplify the output signal but the technology has advanced since then (early 80's) so better light output/sensing may not need the amplifier. It is no big deal to add one. The magnetic approach may still work but may need some shielding. Tin can around all but the pickup side. Even a shaft bump and a capacitive pickup can work. Mr. Kelly, I figured that a picture is worth a thousand words so I put up some photos and layout he http://ballistic.org/wood/router.htm Check it out. Thanks. f. |
#14
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rpm
I am a bit concerned about the distance and angle between source and pickup.
What are you using as a source? Can you shroud the pickup so that less ambient light hits it? However, about all you can do now is to test it- then make modifications. -- Don Kelly @shawcross.ca remove the X to answer ---------------------------- "fritz" wrote in message ... Don Kelly wrote: --- How much space do you have? This can limit options. The machines that I used a photocell on were 5HP units and space, away from couplings, wasn't a problem. There a negative of a picture of a circle with black and white sectors and about 6 inch diameter worked well. the light source and photocell were mounted in a U bracket over the film which was put between two sheets of 2mm plexiglass. Alignment as needed for a reflected signal wasn't critical as one was picking up the direct beam through clear areas on the film. It was necessary to amplify the output signal but the technology has advanced since then (early 80's) so better light output/sensing may not need the amplifier. It is no big deal to add one. The magnetic approach may still work but may need some shielding. Tin can around all but the pickup side. Even a shaft bump and a capacitive pickup can work. Mr. Kelly, I figured that a picture is worth a thousand words so I put up some photos and layout he http://ballistic.org/wood/router.htm Check it out. Thanks. f. |
#15
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rpm
Don Kelly wrote:
I am a bit concerned about the distance and angle between source and pickup. What are you using as a source? Can you shroud the pickup so that less ambient light hits it? However, about all you can do now is to test it- then make modifications. The source I figured would be the smallest halogen 12v bulb inserted inside an Aluminium 1/4" tube with the bulb at the base of the tube and the light exiting about 3/4" later. This would shield the pickup from the light near it. Then the photocell would also be inserted into a tube and positioned deep within it so that this would add to the light shielding. This would effectivley shield the photo cell from the lamp as well as most ambient light. As you say, all I can do is build it and test it. Several years ago I bought a computer addon digital storage oscope (PCS64i) which I haven't tried out but it should give me a good look at the photocell out. Thanks for all the suggestions. It's up to me now to find the appropriate photocell, figure a power supply and check the setup. f. |
#16
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rpm
On 2005-12-30, fritz wrote:
Don Kelly wrote: I am a bit concerned about the distance and angle between source and pickup. What are you using as a source? Can you shroud the pickup so that less ambient light hits it? However, about all you can do now is to test it- then make modifications. The source I figured would be the smallest halogen 12v bulb inserted inside an Aluminium 1/4" tube with the bulb at the base of the tube and the light exiting about 3/4" later. This would shield the pickup from the light near it. Then the photocell would also be inserted into a tube and positioned deep within it so that this would add to the light shielding. This would effectivley shield the photo cell from the lamp as well as most ambient light. if you can paint the inside of the sensor tubes matt black (or use black plastic tubes) that'd help, otherwise the sensor will get reflected light. a high-intensity LED might work better than an incandescent lamp - often they produce a focussed beam, and are certainy more immune to vibrations) As you say, all I can do is build it and test it. Several years ago I bought a computer addon digital storage oscope (PCS64i) which I haven't tried out but it should give me a good look at the photocell out. Thanks for all the suggestions. It's up to me now to find the appropriate photocell, the motor is probablly too fast for a photo-resistive cell (like CdS cells) a photo-transistor or photo-diode is probably the way to go. use shielded cable. it's more important that the photo-sensor only see the shaft than that the light only shine on the shaft, if there's ambient light shining on the shaft what harm can it do? Bye. Jasen |
#17
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rpm
Jasen Betts wrote:
if you can paint the inside of the sensor tubes matt black (or use black plastic tubes) that'd help, otherwise the sensor will get reflected light. a high-intensity LED might work better than an incandescent lamp - often they produce a focussed beam, and are certainy more immune to vibrations) I had thought of painting the inside but I also had thought of unshrunk, heat shrinkable, tubing. A high intensity LED I hadn't. the motor is probablly too fast for a photo-resistive cell (like CdS cells) a photo-transistor or photo-diode is probably the way to go. use shielded cable. it's more important that the photo-sensor only see the shaft than that the light only shine on the shaft, if there's ambient light shining on the shaft what harm can it do? 23,000 rmp is a little less than 400pulses/ps. Is that too fast? I thought that I would do a trial with the LED and one of the radio shack generics hooked up to the little scope. See what I get. After the new year.... thanks f. |
#18
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rpm
the motor is probablly too fast for a photo-resistive cell (like CdS cells)
a photo-transistor or photo-diode is probably the way to go. use shielded cable. it's more important that the photo-sensor only see the shaft than that the light only shine on the shaft, if there's ambient light shining on the shaft what harm can it do? 23,000 rmp is a little less than 400pulses/ps. Is that too fast? I thought that I would do a trial with the LED and one of the radio shack generics hooked up to the little scope. See what I get. After the new year.... I read a cycle time (response time + decay time) of 50ms in a catalogue (I had no luck locating a datasheet) that basically means 20Hz, or 600RPM is the where the signal strength starts dropping in ideal conditions. (this was for an ORP12-ish LDR they also had a lower resistance one with worse performance) photo diodes and photo transistors work up to much higher rates, (remote control applications at 40Khz aren't even close to the limit) 400Hz would be no problem. -- Bye. Jasen |
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