measure motor spindle rpm

[RaceDiagnostics]

I need to measure the speed of a spindle rotating from about 5 to 20rpm.

Is there something off the shelf that I can used to measure and display the RPM.

I don't want to use a hand held gun, it needs to be built into a cabinet.

Any suggestions?

 

[Wedg1e]

There used to be optical tacho kits you could buy that detected the difference between light and dark areas of a rotating shaft, not sure if in this age of digital silliness they are still around... a cleverclogs could probably knock something up with an optosensor and a frequency- voltage converter IC.

 

[brightspark]

http://www.ebay.co.uk/itm/Red-LED-4...018134?hash=item25b8f78116:g:Iy8AAOSwxp9W88Xv

 

[Pete.]

Cheap as you like but to get down to 5rpm you'll have to use multiple magnets because 5rpm is 1 turn in 12 seconds and it auto-clears at 10 seconds.

If you used 10 magnets on a spider-wheel then it would read 50rpm at 5rpm and you'd have tenth resolution just by painting a dot on the readout.

 

[RaceDiagnostics]

http://www.ebay.co.uk/itm/Red-LED-4...018134?hash=item25b8f78116:g:Iy8AAOSwxp9W88Xv

Almost exactly what I need, this one only goes down to 10 rpm but it points me in the right direction.

 

[Gareth J]

I've used a couple of those ∆∆ before, the ones I've tried are quite sensitive to the magnet and all the things associated with it. They seem to skip odd "counts" and flicker between readings if you're not careful but you can normally tell what it's trying to read.

As for that low a speed, is it an output on a gearbox? Maybe you can put the sensor/pickup on a faster part (input motor?) And do some maths with the output.

 

[skotl]

http://www.ebay.co.uk/itm/Red-LED-4...018134?hash=item25b8f78116:g:Iy8AAOSwxp9W88Xv

They look good fun. I've ordered a couple and will try to fit them to the lathe and mill

 

[MoreWellie]

hmmm, tied up to something like https://www.sparkfun.com/products/246 this could give a basic rev counter monitoring a white line or multiple white lines. might be easier than attaching magnets

 

[tomsutton529]

If you mount a disc on the end of the shaft. or of the shaft is big enough just tape something onto it (with some good tape), add some weight to create unbalance and use one of the free vibration apps you can get for smart phones. It will produce a dominant peak at the speed of the motor... any other peaks then you have an issue. If the spectrum is displayed in Hz then multiply this figure by 60.

Should be OK down to 5 RPM if you have enough weight. The higher the speed use less weight... this wont affect the frequency of the peak but will alter the amplitude. you may have to experiment with readings on the Drive end and Non Drive end and see which give you the best result.

 

[WorkshopChris]

They look good fun. I've ordered a couple and will try to fit them to the lathe and mill

Was just looking at them, need to work out the connection details, sometimes this Chinese stuff comes without any documentation.

 

[daleyd]

Can you mount an encoder, some cheap ones on eBay for 10-12 quid. They should give you a much more accurate speed signal than trying to count 1 pulse per revolution at low speeds.

 

[RaceDiagnostics]

Parts ordered, it will be attached to a geared (about 200 to 1) motor, luckily I have access to the motor spindle also that I will used for the speed senor.

I'll get back to it in a few days, today's job was to repair a 20.5MHz radio telescope receiver, work in progress.

 

[Screwdriver]

I bought one of those a while back and am just about to install it on the lathe. There's no wiring diagram for the ribbon connector to the tacho display. Anyone got a wiring diagram?


<edit>

got it, I think!

 

[hunter27]

I bought one of those a while back and am just about to install it on the lathe. There's no wiring diagram for the ribbon connector to the tacho display. Anyone got a wiring diagram?


<edit>

got it, I think!

I bought one of these if it's the same and wired it up on the boats engine. I can't test it properly at the moment as the boat is out of the water and cools by sea water but it worked temporarily on my lathe chuck as a test.
Look here at the bottom of the post and there is a diagram and some listings for this tacho have more info on the wiring. I am sure I found one with pictures of the wiring.

http://www.ebay.co.uk/itm/Blue-4-Digital-LED-Tachometer-RPM-Speed-Meter-Proximity-Switch-Sensor-NPN/322154524098?_trksid=p2047675.c100010.m2109&_trkparms=aid=555012&algo=PW.MBE&ao=2&asc=38661&meid=c38812c565c749e194443d82197ee474&pid=100010&rk=1&rkt=6&sd=172036002887

 

[skotl]

I bought one of those a while back and am just about to install it on the lathe. There's no wiring diagram for the ribbon connector to the tacho display. Anyone got a wiring diagram?


<edit>

got it, I think!

Does it look like either of the units in this post?

 

[Screwdriver]

Does it look like either of the units in this post?

Yep that's the fella. Good info thanks. I'll get around to it soon.