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Practical Wiring - Professional Motorsport: Step 3 - Documentation Detail and Concentric Layer Design

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Step 3 - Documentation Detail and Concentric Layer Design


00:00 - The third step of the HPA 10 step motorsport wiring harness construction process consists of finalising our design and our documentation.
00:09 The design and documentation are grouped into one step as most often you will be undertaking both tasks in tandem, generating your documentation as you progress through the design.
00:20 We're going to draw upon the information from the previous two steps for the details relating to the circuit design and the wire size as well as the physical layout.
00:29 The first step we undertake in this process is to finalise our connector specifications.
00:34 There are three common situations you will strike when specifying a connector.
00:39 The first is the simplest which is when you are making a direct connection to a component of the EFI system and the connector to be used will be reliable in a motorsport environment.
00:49 In this situation, the decision is essentially made for you as you will specify the connector required by the EFI system component.
00:58 A common example of this would be injectors with the US car connectors.
01:02 These connectors have proven to be very reliable and are suitable for motorsport use.
01:07 The second scenario is when you need to make a direct connection to an EFI system component, however the connector on the EFI system component is not suitable for a motorsport environment.
01:18 In this situation the solution is to install a flying lead onto the EFI system component, pot the connection point, and break the flying lead out to a more reliable connector.
01:29 An example of this would be the ignition coil used by Toyota on their 1ZZ series of engines.
01:34 These are commonly used for coil on plug conversions but race history has shown that the OEM connectors become unreliable in a motorsport application due to the harsher vibrations they see.
01:45 In this situation you will need to specify a connector to be installed on the flying lead and Autosport ASL range is a commonly used option.
01:54 The third scenario is when you're making a connection between wiring harnesses.
01:58 This situation is much like the last but without any potting involved, and typically we'll use a connector with a higher pin count as there will be more connections to be made.
02:08 A good example of this is a connection between a main EFI wiring harness and a sub harness that serves the intake manifold.
02:15 The sub harness will be making connections to multiple injectors, sensors, and other parts of the EFI system, and there will be many connections to the main wiring harness required.
02:25 You'll need to specify a connector with enough pin locations of the right size for the wiring and current load.
02:32 Autosport AS or Souriau 8STA connector ranges are a good option for this.
02:39 With all your connectors specified, you can begin to create your documentation by setting out a spreadsheet with sections devoted to each connector.
02:48 With this setup, the next step is to detail the pin out each of these connectors.
02:52 Much like specifying the connectors themselves, often this pin out designation is defined for us when we're making a direct connection to an EFI system component.
03:03 In which case this can be directly recorded on your spreadsheet.
03:06 The situation is a little more complicated when we can define the pin out of the connectors ourselves.
03:11 In this situation we want to take into account our concentric twist layer design.
03:16 The construction of the harness will be much easier if we can, as much as possible, match our concentric twist layer design pattern to our connector pin out decisions.
03:26 In this situation, I will still fill out the documentation section for each connector with the required wires but wait to finalise that pin out until the concentric layer design for that harness section has been completed.
03:39 Which is the next part of the process.
03:41 We covered the concentric layer design process quite thoroughly in the design lessons section of the course, and this is the point where those lessons get applied.
03:49 WIth all the connectors and circuits for the harness specified, you will have all the information to know the exact wires running through any harness section.
03:58 Using this information, you can design your concentric layering for each section.
04:03 Typically this will involve working from the largest wires or cables in a particular harness section, outwards to the smaller wires on the outer layers.
04:12 Including any filler wires that might be needed to complete a layer.
04:15 With the concentric layer pattern for the harness sections detailed, you can now go back to your connector pin out designations and fill them out to match your layer pattern as much as possible.
04:26 Now this will not be possible in all instances.
04:29 Particularly in the case of ECU connections.
04:32 These are quite large connectors with many different types of wiring.
04:36 But the pin out is defined for us by the ECU manufacturer and not something that we can choose.
04:42 In this situation the design process for the concentric twist pattern does not change but the area behind the ECU connector, usually beneath the boot, will end up a little untidy as wires need to change locations around one another to get to their correct layer position.
04:58 This design and documentation process can be an iterative one.
05:02 With the design evolving as you progress through it.
05:05 Often patterns will become apparent and you will alter wire positions as you progress through the process.
05:12 However there are some good guidelines to follow.
05:14 You want to have your concentric twist pattern design drive your pin out definitions as much as possible.
05:22 You want to group wires that branch out together in your concentric twist pattern.
05:26 Try to have them in the same layer and try to have them next to one another if possible.
05:31 Try to have wires that will branch out early at the outer layers and wires that will run the length of the harness in the middle.
05:38 We'll have a look at the documentation and design for our FD3S RX7 harness now, and go over some of the key points.
05:46 The complete documentation is available below the module..
05:49 You can see in the documentation for our FD3S RX7 here we've got our spreadsheet set out, and we've got all our different sections relating to all the connectors that are going to be on the harness.
06:01 We'll have a look at our sensor interface connector here and talk about the decisions behind using our 8STA0 1435SN connector for this application.
06:13 The first key point is that the connector does have the required number of pins to get all of our signals through our bulkhead and into our engine bay.
06:23 Now we have used all 37 pins in this situation and that's not actually particularly common.
06:29 Most often you will be specifying a connector that has more pin locations that you require.
06:35 We just happen to have gotten lucky in this situation that we need to pass 37 wires through and there is a connector available with 37 pins.
06:44 The second key point is that this is a sensor interface connector and we are using 22 gauge wiring for the majority of our sensor signals.
06:54 The one exception to that being our 24 gauge twisted shielded pair thermocouple wiring.
07:01 This connector has size 22 pins, so it is going to be correct for that application as we can reliably crimp our 24 gauge thermocouple wiring into those size 22 pins.
07:14 Speaking of the shielded cable, that is a key point when you're determining the number of pin locations your connector is going to need.
07:22 Each of the shields on our shielded cables are going to get broken out to a wire, and passed through a pin location on the connector.
07:31 This is also a point of flexibility when it comes to the number of wires that need to pass through a connector.
07:38 You can see here that our ref and our sync shielded cables are actually going to have their shields joined together and passed through on a single pin.
07:47 If we were to pass those through individually we would need 38 pins on this connector.
07:53 That would mean that we would have to step up to a larger size.
07:56 So to avoid that, we are going to join those ref and sync cable shields together and pass them through on a single pin.
08:03 If you can avoid doing this, it is best to, but there isn't going to be any downside in this application.
08:10 Particularly as we are grouping our ref and our sync shield cable braids together.
08:16 Those cables head to the same location so they're likely to be susceptible to the same levels of noise.
08:21 You can see also that we can specify the part number of all the pins to be used in this connector which are 38943-22 sockets in this case.
08:32 You'll see there is a change in the part number down here where our thermocouple wiring is going to pass through the connector.
08:39 These are specific pins made of the same material as the thermocouple wire, that's going to keep our unbroken chain of thermocouple material for that entire wire run, back to our sensing element which is going to be an amplifier mounted in the interior of the vehicle.
08:55 Now ordinarily at this connector specification stage, we wouldn't actually have the information about all the pin destinations where this particular pin is going to head off to in the harness finalised yet as that is going to be related to our concentric twist layer design.
09:11 However we have actually undertaken that process already.
09:14 But that is something that's going to happen after you actually specify this connector part number in this position of the harness.
09:22 Up the top here we've got our further connector specifications.
09:25 We've specified the size boot that we're going to be using on it.
09:29 In the connector booting section of the course, we do have that downloadable sheet that shows you our most common boot sizes to be used with the connector shell sizes.
09:40 You can see we've also got details here about the solder sleeve and splice connections that are going to need to be made underneath that boot behind the connector.
09:49 We've got our four solder sleeve connections to our shielded cable braids.
09:52 And we've actually got two splices as well.
09:55 Being our sensor supply or our sensor five volt coming through the connector on a single pin and then splicing out to all the individual sensors and a very similar story for our sensor ground as well.
10:07 Splices are another part of the harness design that you're going to need to specify in quite a lot of detail.
10:12 We have another spreadsheet section down here in which we have detailed all of the splices that are going to be in this harness.
10:20 Each one of these sections includes all of the wires that are going to be included in that splice.
10:26 We've got the location of the splice itself, the overall CMA of the wires included in that splice which has driven the decision of the part number of the splice to be used and also how we're going to insulate that splice as well.
10:40 We've got another spreadsheet here that has sections detailing all of our individual harness sections.
10:48 So that is a part of the harness that runs and terminates to a connector.
10:51 But also the parts of the harness that run between branch points.
10:57 Now at this point with all of our circuits defined, our wire sizes decided upon and our connectors specified, we've got all of the information to know all of the wires that will be in any of our harness sections.
11:10 Using this information we can go through the design process for our concentric twist layup.
11:17 We'll have a look ta the sensor interface to branch point A of our FD3S RX7 here, and talk about how this particular concentric layup design was decided upon.
11:29 We started with our core design, which included our most complicated cable sections.
11:35 That is our twisted pair for our CAN wiring and out twisted shielded pairs for our ref sync knock and our exhaust gas temp sensors as well.
11:42 The initial design was actually to twist all six of these wires together, but I built a small test section of harness and determined that this really wasn't going to be tidily feasible.
11:56 Then I built another test section that was a bit of an experiment, using our CAN bus wiring as a core here and then twisting our larger twisted shielded cables around that.
12:06 Now you can see that this has generated a really nice concentric twist.
12:11 We'll be using this for our coil, we've got good flexibility and it's a nice circular profile there, we've got all of our wires and it really has gone quite well.
12:22 Now this is a concentric layup design that the math that we've talked about wouldn't have actually helped you to achieve.
12:29 And for that reason, sometimes building a test layup section really is the best way to go.
12:35 So this is a test layup section for the core of our harness section that's going from our sensor interface bulkhead connector to branch point A.
12:44 I've got another test layup section here that's for our actuator interface to our branch point A.
12:51 And it really does help you just to confirm the design, knowing that it's going to be reliable, easy as possible to construct and give you that good circular cross section and flexible result that we're looking for.
13:06 We've also got test builds here for the rest of the core of the harness that's actually going to span from branch point A to B and then from B out to these three sensors which are going to be the ref sync and the knock sensors.
13:20 And a test layup here which was actually a very interesting one for our exhaust manifold interface.
13:28 Now this one was especially interesting because there were three larger cable sections that I really wanted to include in the core, being our exhaust gas temperature thermocouple wiring and our twisted pair for our CAN bus.
13:43 Building a test section allowed me to confirm that I will be able to reliably twist these in a trio.
13:49 It'll end up with that good flexibility, everything staying together, and it's got a reasonably circular cross section that once is wrapped in the next layer, will give us the benefits that we're looking for.
14:02 We'll head back over to the laptop now and have a look at some of the math behind the decisions that drive the number of wires in the following layers of the harness.
14:12 We'll have a look in detail at the sensor interface to branch point A section of the harness.
14:19 So as mentioned, the core was decided upon by a test layup.
14:24 So that's given us our configuration here and actually allowed the diameter of that test lay to be directly measured.
14:31 Three measurements were taken of the diameter along the length of the test section and averaged we've got 7.6 millimetres as a finished diameter for that first layer there.
14:41 Now taking that 7.6 millimetres, we can divide that by the diameter of the wires that will make up the next layer.
14:51 Now once we've got our twisted shielded pairs out of the way here and our twisted pair, every other wire in this harness section is going to be 22 gauge.
15:01 So we can take out 7.6 and divide it by the diameter of a 22 gauge wire which is 1.12 millimetres, giving us a result of 6.78, or approximately 6.8 there.
15:13 Looking that up on our cross over reference chart, that's going to give us 23, 22 gauge wires in the next layer of our harness.
15:22 Now we actually have 31, 22 gauge wires that are heading away from this connector through this harness section.
15:30 So we are going to fill up our layer two with all wires that will be carrying signals.
15:37 The decisions around which wires are going to be in layer two, are based around keeping things as grouped as posisble.
15:43 So you can see all of these wires here relate to our exhaust manifold breakout interface there.
15:51 We want to keep those as grouped as possible, much like we've done here for our upper intake manifold break out wiring as well to keep those transition points as tidy as possible.
16:01 Similar situation with our engine fuel pressure sensor wiring which is actually going to be part of our fuel system break out connector.
16:08 The other wires for which are in another harness section at the moment.
16:13 Keeping those grouped together.
16:15 Also our engine oil pressure, engine oil temperature and engine coolant temperature grouped as well.
16:21 Heading up to the third layer of our harness here we're going to need to undertake the same mathematical procedure to determine the number of wires that are going to be in this layer.
16:33 So we've been able to calculate the final finished diameter of our second layer here by taking our measured and known diameter of our layer one, which in this example is really essentially our core, and adding twice the diameter of an individual 22 gauge wire to it.
16:50 So if we take that 7.6 millimetres and add 1.12, twice we get a finished diameter of layer two of 9.84 millimetres.
17:02 Taking that 9.84 millimetres we can divide that by the size of the wires in the next layer which are still 22 gauge.
17:11 So it's gonna be 1.12 millimetres, that gives us a result of 8.78 or essentially 8.8.
17:18 Crossing that over to our look up table there, we get a result of 29, 22 gauge wires are going to wrap nicely around that layer two in our third layer, give us the correct lay length there.
17:32 However we do only have eight 22 gauge wires left in this harness section.
17:37 So that means that we're going to have to add in 21 filler wires to round out this to be a complete layer.
17:45 This is quite a lot of filler wires but it is absolutely fine to have to add those, this is also going to be quite a short harness section so it's not going to add too much extra weight.
17:55 You can see I've specified those filler wires as being violet.
17:59 This is just another colour coding standard that I've personally come up with that I like to stick to.
18:05 i don't use violet for anything else in the harnesses I build usually, so if I see violet wiring in there I do know that it's filler wiring.
18:11 Now that process is completed exactly the same for our actuator interface to our branch point A there.
18:18 And then once again for our branch point A to our branch point B.
18:22 We typically do this progressing along the harness from our ECU connectors out to all the individual sensor connectors.
18:31 Usually it is the easiest way.
18:33 You can see we're doing a similar job here for our branch points to our individual interface connectors now.
18:39 Getting down to our individual sensor connections as well.
18:43 Now a really interesting point with this harness was that once our exhaust gas temperature thermocouple wiring here branched out down our exhaust interface, we were left with those other three twisted shielded pair cables which we've got our example section of twisted together here.
19:05 Those are our ref sync and our knock sensor wiring and they actually form the core of the harness for the entire of the rest of its run.
19:14 This is actually a more common situation than you would first think.
19:19 Extremely often our engine position sensors are at the front of the engine and our wiring harness will be coming through from the bulkhead.
19:27 So the longest run is quite often to those engine position sensors with our shielded cable.
19:33 This is actually a great help as shielded wiring like this does make a really good core for our harnress.
19:39 I would strongly suggest downloading this document and getting familiar with it as a guide to the level of detail required for a motorsport harness build.