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  #16 (permalink)  
Old 01-18-2012, 07:20 AM
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mercmad63,
The shafts have seals that press into the stators from the outside. I have solenoid valves controlling the load. I will probably add a larger motor controlled valve later if PWM doesn't work with solenoids.

Gow,
I hadn't seen that one before. Land and Sea has one also, but the AEM is cheap. I had thought about measuring torque on the shaft like that with some strain gauges. Figuring out the wireless is what has kept from it for now.

Wags,
I had just posted some pics of my adjustable stand on the other thread. I started getting some private messages and answered some questions over there so I started this thread. I have pics of the unassembled brake in my gallery if you want to try to make one.

Kevin

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  #17 (permalink)  
Old 01-18-2012, 09:27 AM
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Quote:
Originally Posted by KA67_72
Wags,
I had just posted some pics of my adjustable stand on the other thread. I started getting some private messages and answered some questions over there so I started this thread. I have pics of the unassembled brake in my gallery if you want to try to make one.

Kevin
Thanks Kevin, I'll check those out

Wags
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  #18 (permalink)  
Old 01-19-2012, 03:52 PM
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Got home tonight and started working on EGT's. Normal EGT probes are shielded, but they aren't cheap and I think bare ones will respond faster. For dyno use they should be plenty durable. I have a bare K-type I use to measure the temp of molten aluminum, which is super corrosive, and it has survived. I have 50' of K-type wire I bought for like $30 online. I decided to try TIG welding the junction. It looks just like the store bought ones. Seven more to go.

Kevin
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Old 01-19-2012, 05:16 PM
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What ever probes you use for the EGT, I would try to use all the same probes in the same condition. he relevant information is not as much about temp as it is about trends and comparisons cyl to cyl.
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  #20 (permalink)  
Old 01-19-2012, 08:48 PM
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That water brake looks nice. I have put together my own rolling road dyno using an old eddie current retarder. I have built my own controller/data aquasition system. I would like to build an engine dyno in the furture as well, so Im keen to see your progress with this.

From my research it seems most control systems use motorised valves (servo valves) to control the load. I'm interested to hear how your PWM valve setup goes. Can you tell me what valves you are using with the PWM setup?

Cheers

Daniel.
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Old 01-19-2012, 10:22 PM
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Me too...........

I have an eddy current roller dyno and have started on the home built closed loop speed control system for it, but it is going to be a very long term project.

Controlling a water brake is pretty much the same, except you need either a motorized valve, or speed controlled pump to vary dyno load, instead of just varying the current through the retarder which is a lot simpler.

But the cosed loop speed control system is going to be pretty much the same, whatever type of dyno you are building.

My system uses an optical chopper disc that generates a frequency, that is used to both control the dyno loading, and read the roller speed for calculating power.

The engine speed setting knob varies the frequency of an oscillator.
The frequencies coming out of the optical chopper, and the oscillator are compared in a frequency/phase comparator chip, and that ramps the dyno lad up and down to hold engine speed EXACTLY where I want it to be.

So I set my oscillator to the equivalent of maybe 4,200 rpm and the engine idles under zero load.
I open the throttle and the revs rise, until the engine reaches 4,200 rpm, then the dyno load builds up very fast and holds the engine at exactly 4,200 rpm.

If it drops to 4,199 rpm the load backs off very slightly, if it rises to 4,201 rpm the load builds up very slightly.
It hold engine rpm steady as a rock at any throttle opening above idle at whatever rpm I want to test at.
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  #22 (permalink)  
Old 01-20-2012, 12:02 AM
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Controlling the speed of the pump is an interesting idea, I haven't seen that before.

My system is based on a microcontroller which reads pulses from a hall effect sensor. It calculates the rpm and uses a PID loop in the code to control the speed. It also does ramp runs etc. The controller also handles the other sensors like the load cell and air temp as well as other spare analogue channels. The controller then feeds the info to the pc for displaying and logging. I have been working on my system for 3 years and have 2 mates in Melbourne who have my system on their dynos.

Cheers

Daniel.
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  #23 (permalink)  
Old 01-20-2012, 12:46 AM
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I am using a microcontroller only for monitoring outputs and digital readout.

The control system is all in hardware, and really very simple with few components.
It uses a proportional integral loop (PI) and drives the retarder coils through a PWM system (500Hz), which responds much faster, and is more linear in operation than the usual mains phase control.
The speed and linearity make PI loop tuning far easier, and with a much tighter and faster acting load control.

I have seen a centrifugal pump run off a VFD to pump water from a cooling tower sump into the water brake. The water brake itself discharges hot water through a metering orifice to the spray at the top of the cooling tower.

That seems to respond faster and give much better load control than some of the very slow to respond commercial motorised valves. You will probably need a pump anyway, so might as well control the pump speed directly rather than throttling it.

I am not at the stage of sweep testing, and may never bother with sweep testing.
But for mapping EFI systems, what I have works wonderfully well. It is all in pieces at the moment, must get back into it.....

If you are going to be sweeping your water brake, control of water flow volume into the brake will need to be both fast acting and fairly linear.
If it is slow and hugely non linear, you are going to have a lot more difficulty tuning your PID loop for both speed of response and stability.
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Old 01-20-2012, 03:25 PM
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I have an old Clayton chassis dyno. It's water brake has a water jacket with a temperature actuated water heater safety type valve on it. The water used to load it recirculates in the pump and is cooled by the jacket. It's only good to around 400 whp so I plan on upgrading the brake but it works pretty well within it's ratings. I'd like to play with an eddy current brake, but I haven't found one in my price range and they look expensive to make. Right now I'm just using $15 sprinkler valves on the engine dyno. I think they're way too slow to control load other than fill and drain at one rate. I will most likely end up using a stepper or servo controlled valve. Here's the load cell cal I've been working on this afternoon. I made an arm to easily locate my rusty NIST traceable barbell weights at two and three foot.
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Old 02-04-2012, 12:07 AM
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Hi,

Great thread.

I'm very interested in your progress and planning a similar project myself.

I'd love to see more details of how you are coupling the dyno to the test engine. I noticed you are using an equal number of vanes in stator and rotor - I read somewhere that normally there would be a different number?

How is your project progressing?

Cheers.
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  #26 (permalink)  
Old 02-04-2012, 06:37 AM
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I'm using a PTO flange from a jet boat supplier. They are drilled to bolt to a standard spicer flange. This one accepts 1350 a u-joint. I have an H-bar, double cardan cv, and a 1.5" 10 spline yoke to slide over the shaft on the brake. I don't know about the uneven numbered vanes, but it'd be easy enough to experement with. Right now I'm working on noise control and still learning about microprocessors so I can cheaply collect more data. I have the hardware to log 15 thermocouples, and the load cell, and 70 digital i/o points through one $10 chip. I just need to learn how to program it.

Kevin
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Old 02-04-2012, 01:52 PM
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Every commercial water brake has the vane count on the rotor and stator different by one vane. Most commonly 11/12 vanes, or 12/13 vanes.
This creates a very smooth torque absorption characteristic, as the vanes pass each other one at a time.

If you have the same identical number of vanes on both sides, the vanes will all line up and pass each other together, and there could be some significant torque pulsing every time the vanes simultaneously line up all the way around.

It will certainly work with the same number of vanes, but if you get some very strange noises or vibrations at certain speeds, you will know what needs to be done.
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Old 02-05-2012, 07:47 AM
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What stops axial movement of the rotor shaft? I guess that the rotor is keyed onto the main shaft but what stops the rotor from moving front to back and the rotor from hitting the stator?

I have started to draw something up and wondering about using thrust washers either side of the rotor to keep it central in the body.

For your materials am I right that the body and stators are aluminium and the rotor stainless? What did you use for the main shaft?

My main concern with mine is the data acquisiton - I'm happy with the mechanical and machining but will be a steep learning curve on the data side of things.

Cheers.
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  #29 (permalink)  
Old 02-18-2012, 07:36 PM
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Here's a short video of the motor on the dyno. I had an issue logging RPM so there's no HP. Peak torque has only been 363 lbs. I'm going to try to find some more power before upping the limiter from 5k, switching to fuel injection, and adding boost. I may also put some headers on it and see what it does first. It has 1.94" Double Humps on it that seem to like a lot of timing. I started the day with timing at 36 degrees. I'm currently at 42 degrees and up 113 lb of torque. It's pig rich, but I figured I'd get the timing down first. On the second pull I flipped the wrong switch and caused all the steam. If I leave the water on it works better, but I'm going to have to add a pump and tank soon.

http://www.youtube.com/watch?v=JqEvs...4J55Gml2s-Rvlh

mtrehy,
Sorry I missed your post earlier. This one is all steel. The rotor is welded to the shaft. All four bearings have eccentric collars.
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Old 05-03-2012, 01:29 AM
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Hey Kevin, many thanks for starting this thread . . . and to all others who have contributed. I have been thinking about this for quite a while. Have a few questions but no time at the moment. I need to re-read it a few times. Some pretty creative stuff here . . .
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