Reply To: Model Turbines

[SillyOldDufferModerator @sillyoldduffer]

Posted by Mike Tilby on 06/09/2020 22:14:52:

Hi Dave

I'd like to look at the article you mentioned in which you describe your shaft torsion dynamometer. Can you please tell me the issue/year of MEW in which it appeared? I am wondering if it would be a more suitable alternative to the water-brake dyno that I have partly built. I am thinking it would enable me to have automated data collection without having to tackle the electronics needed for analysing a load cell. I feel happier about using optical sensors and microcontrollers since I've used them before.

Are there any problems with that type compared to the water brake type? e.g. calibrating the torsion shaft which I guess is done using static weights hanging off of a lever?

I'm not sure, but I think the first torsion dynamometer was the one invented by Charles Parsons in order to investigate lack of power in the Turbinia. His dynamometer is on display here in the Discovery Museum in Newcastle and led to the Denny Brothers of Dumbarton developing the shaft torsion dynamometer for use in the ships they built.

Regards

Mike

Now you're asking. I'm disorganised! I'll have to look through my mags to see if I can find it. Fairly sure it was the first half of 2017 but I might be wrong.

I'll have to check the old book I got the info from: I think it predates Parsons but could be wrong. Calibration as you say by hanging weights on a lever, though that's not necessary if you have the steel's specification.

There's also a mostly complete Arduino project developed in collaboration with Duncan Webster intended for a Dynamometer car he's been working on. The Arduino captures load cell values on each wheel revolution and the time of each revolution. The data is copied to an SD card or streamed to a connected PC. A program on the PC calculates rpm and power etc from the raw data and draws graphs. Been tested with a simulator but not on the track.

Probably the main disadvantage of the torsion type is the long 'spring'. Not as compact as other types. Easy enough to set up and calibrate though. The Arduino and photosensors measure the angular twist by detecting the time difference between two normally aligned holes in discs at each end other spring. The disc next to the load lags behind the one at the engine end.

Dave