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Old 08-27-2013, 02:58 PM   #31
ttpete
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How are you going to balance it? On a pair of knife edges? That was the old way.
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Old 08-27-2013, 04:24 PM   #32
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Originally Posted by ttpete View Post
How are you going to balance it? On a pair of knife edges? That was the old way.

If it's solid steel and it's machined true, I can't see that it will be out of balance.
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Old 08-27-2013, 05:39 PM   #33
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PJ is right, if machined true - no need for balance. It's true!
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Old 08-27-2013, 06:08 PM   #34
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Originally Posted by drhach View Post
Is this really cheaper/easier than building a brake dyno?
The design and therefore manufacturing methods are more complex than the usual DIY inertia dyno because I'm lucky enough to have access to kick-arse facilities.

You can make it simpler.

One common method is to turn short stub axles down from the solid lump. Again no dynamic balancing required. Material + machining for this in Aust would be about $1400. Software + pickup $1000. + material for frame and bits and bobs you can have a very good dyno for around $3000.

There are other cheaper ideas for the rotating mass. An interesting one is to get a scrap 3 phase induction motor (a big one!), cut a window in the case to expose the rotor, run motorcycle wheel directly on rotor! The rotor is already balanced and mounted on it's bearings and designed to spin 1500RPM+ depending on number of poles. Obviously would have to check that bearings are OK.

You can build a cheap brake style dyno using an electric motor or water pump or eddy current brake etc for a load. The trouble is, they are notoriously inconsistent from pull to pull due to heating effects and hysteresis and stuff. Compensating for these effects becomes complex.

The inertia style is the most common DIY style of dyno because it is relatively easy to build an accurate dyno with good repeatability.
Main down side is that it is pretty useless at giving you a picture of what's going on below around 3000RPM engine speed and not very good for things like mapping EFI.

goggle 'DIY dyno' - lots out there.
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adrenal screwed with this post 09-02-2013 at 07:31 PM
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Old 08-27-2013, 06:31 PM   #35
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PJ is right, if machined true - no need for balance. It's true!
I suppose it wouldn't matter at the speed that that will run.

When I was working with gas turbine development years ago, EVERYTHING was balance checked. We found that even a symmetrically machined compressor test rig shaft needed some correction. A few milligrams are a big deal at 50,000 RPM+.
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Old 08-27-2013, 08:26 PM   #36
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Quote:
Originally Posted by ttpete View Post
I suppose it wouldn't matter at the speed that that will run.

When I was working with gas turbine development years ago, EVERYTHING was balance checked. We found that even a symmetrically machined compressor test rig shaft needed some correction. A few milligrams are a big deal at 50,000 RPM+.
Yeah, different league that. Still, the dyno wheels can get up to 3000RPM+ not a nice look if 1/2T steel goes ferral and takes 3 walls to stop!

BTW: What the Iron lady failed to recognise, or willfully ignored, is that capitalism suffers exactly the same problem!
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adrenal screwed with this post 08-27-2013 at 09:25 PM
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Old 08-27-2013, 09:57 PM   #37
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Originally Posted by adrenal View Post
Yeah, different league that. Still, the dyno wheels can get up to 3000RPM+ not a nice look if 1/2T steel goes ferral and takes 3 walls to stop!

BTW: What the Iron lady failed to recognise, or willfully ignored, is that capitalism suffers exactly the same problem!
Well, no. Capitalists hand out jobs, not free money. " No money, what a shame. Report here tomorrow, and you can earn some money to buy groceries and pay the rent. And you'll have pride in that you didn't have to accept charity instead of suckling off people who DO work for a living".
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Old 08-27-2013, 11:45 PM   #38
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Well, no. Capitalists hand out jobs, not free money. " No money, what a shame. Report here tomorrow, and you can earn some money to buy groceries and pay the rent. And you'll have pride in that you didn't have to accept charity instead of suckling off people who DO work for a living".
No qualms about that ttpete (except for the issue of structural unemployment), but the system is still fuelled by 'other peoples money' ie: the consumer. And when that runs out, it is fuelled by debt thru ponsie banking systems based on virtual money and financial instruments. Very prone to collapse! Bring back the Gold standard and Glass-Steagall!
Anyway, shouldn't have poked the tiger and hyjacked my own thread. Back to dyno's!
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adrenal screwed with this post 08-28-2013 at 12:33 AM
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Old 08-28-2013, 05:46 AM   #39
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Cutting cross grooves for wheel traction

Loaded into CNC lathe with live tooling








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Old 08-28-2013, 06:02 AM   #40
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Originally Posted by pommie john View Post
If it's solid steel and it's machined true, I can't see that it will be out of balance.


mmm, machined and balanced aren't the same. even for solid pieces. the larger the piece, or greater the mass, the more out of balance it can be. i'm no engineer though, so there is likely a formula i'm missing.
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Old 08-28-2013, 06:13 AM   #41
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I hope it's still in balance after the grooves have been machined
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Old 08-28-2013, 07:18 AM   #42
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I hope it's still in balance after the grooves have been machined
So do I!!!
Solid carbide tool and very shallow cut so there shouldn't have been too much tool wear. Also that machine is pretty accurate. We'll see what happens during the first pull
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Old 08-28-2013, 08:31 AM   #43
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Thanks. I know that cooling is the trick with brake dynos and that Hysteresis is a big issue. I guess from where I'm sitting, it doesn't seem to much harder to solve that the measures that you are taking for the inertia dyno. However, if the inertia dyno suits your needs then that's good enough. I don't have the means to build either one. So there ya go. Great work by the way.





Quote:
Originally Posted by adrenal View Post
My design and therefore manufacturing methods are more complex than the usual DIY inertia dyno because I'm lucky enough to have access to kick-arse facilities.

You can make it simpler.

One common method is to turn short stub axles down from the solid lump. Again no dynamic balancing required. Material + machining for this in Aust would be about $1400. Software + pickup $1000. + material for frame and bits and bobs you can have a very good dyno for around $3000.

There are other cheaper ideas for the rotating mass. An interesting one is to get a scrap 3 phase induction motor (a big one!), cut a window in the case to expose the rotor, run motorcycle wheel directly on rotor! The rotor is already balanced and mounted on it's bearings and designed to spin 1500RPM+ depending on number of poles. Obviously would have to check that bearings are OK.

You can build a cheap brake style dyno using an electric motor or water pump or eddy current brake etc for a load. The trouble is, they are notoriously inconsistent from pull to pull due to heating effects and hysteresis and stuff. Compensating for these effects becomes complex.

The inertia style is the most common DIY style of dyno because it is relatively easy to build an accurate dyno with good repeatability.
Main down side is that it is pretty useless at giving you a picture of what's going on below around 3000RPM engine speed and not very good for things like mapping EFI.

goggle 'DIY dyno' - lots out there.
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Old 08-28-2013, 04:16 PM   #44
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at one time I worked for a company that made small to medium size engines, 1 cyl to 6 cyl. We used solid machined flywheels and we always balanced them. They always needed balancing. Solid steel isn't always the same density all over I guess.
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Old 08-28-2013, 05:53 PM   #45
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static balancing the lump o steel should be minimal fuss. simply mount in two low friction bearings. process should be substantially same as video below.

this has got to be the clearest how to balance a wheel video anywhere.

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