Thread: Hand Held RPM meter (tacho)

Thanks Fred.

Simon,
I'll chase up a copy of the MEW mag.

Chris

I bought one of the $7 strobe type tachos from the Peoples Repuplic of China , last year . Works fine . I took it into TAFE and the teachers were impressed with it . The reflective tape tends to fly off , needs to be firmly stuck on. Mike . PS I did the RPM check on the lathe spindle and got a laminated page printed out , a simple chart ..stuck it on the wall

Originally Posted by simonl

Also the accuracy of any of these methods including the handheld optical ones would be plenty for determining the RPM for turning speeds. I would imagine they would have a typical error of about 1%. So even at 2000 RPM, error would be no more than +/- 20 RPM.

The trick with those hand held reflective tacho’s is to point them at a single fluro tube. That triggers them, at 50Hz, you should get a reading of 3,000 on the meter. (50 per second x 60)

Regards Phil.

Thanks fellas. My lathe already has a plate on the front which tells me the RPM for any given combination of belt settings. However, I'd prefer an instant readout of RPM, rather than having to open the headstock cover and work out what the current setting is. I know it only takes a few seconds, but I'm lazy.

Phil,
I don't own one yet, but that sounds like a brilliant idea.

Dave

Originally Posted by Dave J

I don't own one yet, but that sounds like a brilliant idea.

Just for the record, is wasn’t my idea, that come in the instructions with the first one I bought years ago.

And be aware, its not an instrument quality check. Electricity supply frequency can fluctuate. I think the supply guarantee down here is something like 48.5 hz – 52hz. Its generally pretty close to 50, but try that on one of those stinking hot summer days, when everyone is using AC, and they are threatening rolling blackouts to offload supply, it will be slow.

But it will tell you if the meter is working, with in reason.

Regards Phil.

Originally Posted by unixbigot

I built my own tachometer using a microcontroller board (an arduino clone called RBBB), a 16x2 LCD and a hall-effect sensor.

With a tiny rare-earth magnet hot-glued to a shaft or pulley, it displays RPM. Also, if you select a work diameter (using up/down buttons in 5mm increments) it reads out the surface speed directly.

Must ask my son he plays with this stuff all the time.
Just finished doing a similar one for Sydney Uni.

Russell

Originally Posted by Matt McLeod

unixbigot, that looks like a nice little project where I could generate smoke instead of swarf.

I couldn't find much on Mr Google but I was probably searching for the wrong thing.

Are plans/instructions in the public domain?

Cheers,
Matt

I haven't quite finished writing up the doco yet, but when I do it will be at Make The Future

The code and schematic (eagle CAD format) is available right now at https://github.com/unixbigot/Spin-Doctor (RPM and mpm/fpm mode (for machine tools) works, kmh/mph mode (for vehicles) isn't complete). The pin assignments are documented in comments in the source code file.

I tried the bicycle computer tacho idea. It's a great concept, but is limited by the maximum speed of the computer.

The idea is simple- you set the units to KPH and the wheel circumference to 167cm. The computer will then read 10's of RPM. i.e. 1 KPH=10 RPM. The only problem is that my computer is limited to 95 KPH, meaning it's not useable as a tacho above 950 RPM. I suspect most bike computers have a similar limitation.

unixbigot,
please keep us posted on your progress. I'd like to build your tacho if you don't mind sharing the details.

Chris

Some bicycle speedos go to 300. I used to have one on a motor bike. In fact I still have it somewhere. I will have a look later. I think the brand was Sigma.

Bryan,
that's great if it's true. Is yours one of these?

SIGMA SPORT® online - Bike Computer, Puls Computer, Beleuchtung

Hi unixbigot,

Good project, I'll be interested to see some finished pictures, I have a half finished tacho project for the mill. Using a pic, and driving an air-core analog meter (just to get the 270 degree travel)

Regards
Ray

Jack, I couldn't find mine, but I think that would be the company. But looking at that site made me realise mine would be over ten years old, and any resemblance to current products would be purely coincidental. I should have said, "In the olden days..."

I checked the RPM on my Standaco mill drill. The Chinese tacho reads somewhat higher than what is written on the speed chart on the machine. I tend to believe the tacho . eg the chart says the slowest is 75 rpm but the tacho says about 100... this goes on through the range with the tacho indicating higher than what the 50 hz chart says. MIKE