Monthly Archives: July 2012

PID FTW

Amazing.  I should have gone to engineering school.  Apparently what I have been building with my tilt sensor and E/P transducer is a PID loop or proportional–integral–derivative controller.  And to make it worse there are numerous algorithms already defined using variables that have real names like “deadband” and “gain”.

I am working with Enfield Technologies, the experts in proportional control of pneumatics, and I think they have a product that would be more suited for our needs.

Enfield Technologies M1D

0.002 is the noise in G’s that we can expect to hear on the Phidgets board so if the last value is +- 0.002 then ignore it?

Hysteresis is 5%, is that our deadband?  5% of the total range?

Interval is 4ms (250 samples per second) limited by the Phidgets (the Enfield is 2.8ms)

Kp of 1
Ki of 0.02
Kd of 1

Motion Tests Day 8

Nothing but trouble.  Installed the lateral spring assist assemblies and it appeared that the right roll transducer failed.  Next time I fired up the compressor the rear pitch transducer wasn’t working so I am guessing it is an icing problem because of the humidity.

Tests I ran ended up punching a small hole in the bottom sheathing because of a improperly placed support I made for transport.  Then I ended up breaking the wood bottom plate for the right roll actuator.  And there are noises from the left roll actuator’s linear bearing (probably damaged from side-load before I added the U-joints to the bottom of the roll actuators).

Overall very depressing!

I started looking at E/P Proportional 2/3 Valves last night but the cheapest I could find was $550.  I was looking for cheaper ones on eBay but found I found these 500-EH transducers on eBay for a fraction of the cost I paid for the replacement left roll transducer.  So I got to thinking that I can simulate a proportional valve programmatically by connecting the opposite transducer to the top port on the actuator.  Not sure if that will give me more control or not – I am also looking at flow control valves.

Grounding

My dad and I got in a discussion about the grounding rod which is recommended in all cases by the generator manufacturer.  I told him that it just wasn’t feasible for a guy with a mobile attraction to drive a 4′ stake in the ground – a lot of times I will just be in the middle of a parking lot or tarmac!

250.34 Portable and Vehicle-Mounted Generators.
(A) Portable Generators. The frame of a portable generator shall not be required to be connected to a grounding electrode as defined in 250.52 for a system supplied by the generator under the following conditions:
(1) The generator supplies only equipment mounted on the generator, cord-and-plug-connected equipment through receptacles mounted on the generator, or both, and
(2) The non–current-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are bonded to the generator frame.
(B) Vehicle-Mounted Generators. The frame of a vehicle shall not be required to be connected to a grounding electrode as defined in 250.52 for a system supplied by a generator located on this vehicle under the following conditions:
(1) The frame of the generator is bonded to the vehicle frame, and
(2) The generator supplies only equipment located on the vehicle or cord-and-plug-connected equipment through receptacles mounted on the vehicle, or both equipment located on the vehicle and cord-and-plug-connected equipment through receptacles mounted on the vehicle or on the generator, and
(3) The non–current-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are bonded to the generator frame.

Ultimately, a guy on one of the forums that I like put it best.  It is a “floating ground” the same as the generator (alternator) battery and chassis ground in your car.  It is a closed system, every electron that leaves the alternator returns to the alternator… period.

ECS and APU

On the ECS (Environmental Control System) front we made a decision to get a CR-2550 (latest generation smaller unit) because it has backup heat coils and the AUTO mode works better than on the CR-7000.


On the APU (Auxiliary Power Unit) front we ran some tests this weekend using an APC SC 1500 UPS.  These were done with and without the APC LE1200.  With the compressor running on our 550W air conditioning test unit we had very steady power from the DuroMax XP4400.  When the air conditioning compressor shuts off it takes an eternity for the SC 1500 to go back online with the LE1200 connected (very strange).

 

Ultimately it appears that with a minimum load of 500W aside from the UPS load and NOT using the LE1200 the generator works great.

I ordered an automatic switch from shore power to generator power when generator power is present.

Generator

My dad purchased one of these 3500W units for $300… best deal going.  Includes 220V service, 120V service, 12V service.  Runs pretty smooth and surprisingly quiet for 7HP.


We connected a 520W air conditioner directly to the generator.  With the other plug we connected an APC RS 700 UPS (line interactive) with about 160W load on the UPS.


The UPS would stay online with the low sensitivity setting and widest berth on allowable voltages but each time the compressor would kick on in the AC because of the thermostat we would lose enough that it would have to switch to battery for a few seconds.


Finally we tried the above power line conditioner. It didn’t seem to help the UPS at all regarding the sensitivity setting (comes from the factory on “medium”). I am definitely not sold on this unit.

We are going to do some more tests this weekend with and without the power line conditioner but using APC SC 1500 UPS instead.

ClimateRight

Struck a deal with ClimateRight today to evaluate the CR-7000 for our application.  This unit does not have heating element (heat pump only).


The main concern is when the weather is below 32°F the heat pump is ineffective.  Fortunately we only hit overnight lows below 32°F in December, January, and February on average.

A small space heater could easily make up for the difference like this 200W (683 BTU) unit from Lasko.

Sizing Climate Control

I recently chose a manufacturer and design for my heater and air conditioner.  They offer different size models based on cubic feet of space.  I am looking at 200 cubic feet of area plus 1000W of heat dissipation from equipment and 400W of heat dissipation from occupants.  The question came up about the design for insulation.  Right now we have R-26 for half the floor (R-10 on the other half but that can be increased if there is room in the avionics bay), R-7 average on the walls, and I suppose I could put batting up in the peak which is just airspace anyway.

The following is specific to my location. You can get your own recommendations by visiting their website.

R-Value Recommendations for New Buildings

Heating System: Natural Gas Furnace
Cooling System: Electric Air Conditioning
First 3 digits of ZIP code: 662
Location: Shawnee, KS

Wood-Framed Building
Insulation Location R-Value* Notes
Attic 49
Cathedral ceiling 38
Floor 25 Over unheated, uninsulated space.
Wall sheathing 5 It is important to use both the insulative sheathing and cavity insulation recommended. Insulative sheathing may be placed outside of wood sheathing product, or special braces can be used.
Wall cavity 15
OVE wall cavity 21 This recommendation assumes that a 2×6 wall can be built for the same cost as a 2×4 wall, using a careful design procedure called Optimum Value Engineering (OVE). Discuss this option with your builder.
Concrete or masonry wall 15.6 Insulation should be placed on the exterior side of an above-grade wall.
Band joist 30 A band joist is a part of a floor joist system (see Fig. 1). This part of the exterior wall must be insulated before the floor is installed.
Basements and Foundations
Insulation Location R-Value* Notes
Slab edge 8 Extend the slab insulation 2 feet below ground level.
Crawl space wall 25 Crawl space walls are only insulated if the crawl space is unvented and the floor above the crawl space is uninsulated.
Basement wall exterior 12 Exterior insulation on a below-grade wall is used only if you choose not to insulate the interior side of your basement wall.
Basement wall interior 11 Interior insulation on a below-grade wall is used only if you choose not to insulate the exterior side of your basement wall.
Metal-Framed Building
The recommended insulation levels for metal frames will not necessarily give you performance as good as the recommended levels for a wood-framed building. Please see the discussion about Design Option: Metal Framing.
Insulation Location R-Value* Notes
Floor 25 Over unheated, uninsulated space.
Attic cavity 49
Wall sheathing 10 It is important to use both the insulative sheathing and cavity insulation recommended. Insulative sheathing may be placed outside of wood sheathing product, or special braces may be used.
Wall cavity 15