Laser photo tachometer arrived, playing around with it

nasukaren's picture

Well, the postal carrier came and left without leaving me an ESC + servo tester, so I still can't install the HXT outrunner. But, she did leave me a little package from Hong Kong that contained the laser photo tachomoter that I ordered from ebay. I'm still amazed at just how cheap Chinese manufacturers are pumping things out. A laser tach would have cost me over a $100 just a few years ago, now I can buy one for $23 w/ shipping from Hong Kong. Incredible.

The quality of the unit is quite good. The laser beam is nice and coherent with minimal spread. The unit is sensitive enough that I could do my motor readings using some duct tape rather than expensive retroreflective tape (that they kindly include a small sample of with the unit).

This will be lots of fun.

Anyway, I went ahead and did some motor speed readings on my Boxer to check out my gear ratios. This is with the back wheel raised on the center stand (no load test):

Motor spindle speed / front hub speed: 3272 rpm
Rear spindle speed / flywheel speed: 2091 rpm
Wheel speed: 168.8 rpm (14 mph)

Motor amp draw was 5 amps, so close to no load. From this, I can see that my motor to wheel ratio with the 1.5" front sprocket is 19:1 rather than the 39:1 calculated by using the gear ratios (I think there is another gear inside the flywheel that I didn't consider). When the motor is at full speed, the wheel is going at 14 mph.

Anyway, I'm glad I got the tach since it's telling me the real motor:wheel ratio rather than the calculated one, which was always a bit iffy since I had a centrifugal clutch and could never test the entire system.

For $23, the laser photo tach is definitely a good buy and it'll be even more useful when I get the HXT mounted and have a variety of volts and amps combinations to play with with the new controller.


After zapping the moped with the tach a couple of times, I decided to take it out for another spin. Seems like the battery is coming up to speed after a couple of charge/discharge cycles as I was able to get 5.0 Ah out of it today.

Trip distance: 5.3 km (3.3 miles)
Moving time: 26 minutes
Moving average: 12.2 kph (7.5 mph)
Max speed: 18.3 kph (11.1 mph)

Total energy: 5.0 Ah
Total Energy: 0.11 KWh
Peak amps: 22.14 A
Min voltage: 21.05 V

km / kWh: 48 km / kWh (30 miles per kWh)

I have some NiMHs on order, I can't wait until they arrive too! Running on two 7 Ah SLAs stinks!

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Re: Laser photo tachometer arrived, playing around with it

Looks a lot like mine. I've got the DT-2234C+ one for about what you paid for yours. IIRC, it's basically the same as the one you have, but runs on a 9V and looks a little different.

I've never used any of the reflective tape, either. I just use masking tape. First day I got it, I was browsing around the house for motors and stuff that I could measure. Heh. :P

Re: Laser photo tachometer arrived, playing around with it

Link -

Yeah, mine is the DT2234A and runs on 3 x AAs.

5 digit LCD
2.5 to 99,999 rpm
Accuracy +/- (0.05% + 1 digit)
Sampling time: 0.8 sec (over 60 rpm)

Darn, I've run out of things to measure!

I was totally this way the first time I got my optical thermometer too. :-)


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