How would you measure tip speed on a hydraulically powered mower blade?

[MossRoad]

This seems like an interesting project.

The question came up to me of "what is the tip speed of your mower blades?"

The mower deck is hydraulic, so the only shaft I could measure speed on would be the shaft coming out of the hydraulic motor. The center spindle is direct driven by that shaft, so it would be accurate.

I used to have access to a tachometer that has a wheel I could press on the shaft to get speed. Then I could calculate from that. I don't have access to that tach anymore.

How would you go about measuring the RPMs of that shaft?

 

[4570Man]

Tachometers are pretty cheap for entry level ones. Do you know the flow into the motor and the motor volume?

 

[MossRoad]

Tachometers are pretty cheap for entry level ones. Do you know the flow into the motor and the motor volume?

Yes, but that can vary with throttle on the engine, which varies the RPMs of the pump, affecting flow calculations. I'd need an engine tachometer and assume that the 20 year old pump and motor, and hoses, valves, etc... have no leakage, slippage etc....

I'd like to measure right at the beast itself.

 

[MossRoad]

White paint strip and an adjustable strobe light?

 

[MossRoad]

Hmm.... found a bunch of them for under $30 on-line. Will have to look at them.

Here's one at Walmart for $12. Some kind of laser doohickey with reflective tape for the shaft. Comes with a whopping three, yes 3, reflective strips! :laughing:

https://www.walmart.com/ip/Handheld...MI0N_Bjq_s4gIVA1YNCh31cgBFEAQYBCABEgI26fD_BwE

 

[MossRoad]

Here's one for $20 with one (1) reflective strip.
https://www.walmart.com/ip/Handheld...MI0N_Bjq_s4gIVA1YNCh31cgBFEAQYAyABEgI7ufD_BwE

 

[MossRoad]

Harbor Freight $38.
Digital Photo Sensor Tachometer

 

[RSR]

A hall effect sensor. You can buy one for about $10 on Amazon. You'd have to wire it up to a monitor, though. Or, you could buy one packaged as a bicycle cyclometer (speedometer), for about $20-$30. Simply place/fix a small magnet on the blade, and place the sensor within about 1/4" as it passes by. If you go the bicycle speedometer route, you'll have to back out RPM based on the circumference of the "tire" that is set on the cyclometer. V = RPM x pi x D. Just be careful with units when making the calculation.

 

[RSR]

Bicycle cyclometer

https://www.amazon.com/Speedometer-...t=&hvlocphy=9005312&hvtargid=pla-727449593694

The advantage with it is it could be placed permanently, and monitored in real time.

 

[MossRoad]

I guess that was too easy. I'll be looking at a few and get one sometime in the near future and report back. Thanks.