- Hey team, Andre from High Performance Academy here, welcome along to another one of our webinars.
Just wanted to talk today a little bit about some of the things that we can do with
a aftermarket dash unit.
And this is relevant to us because we have just got back from a day of testing at Teretonga
Motorsport Park which is a couple of hours south of us here in Queenstown.
We have got a new project that we are getting ready for the racing season which is now only
about 4 weeks away.
This is a Honda EF shape CRX and it's powered by a built K20.
We'll just dive across to my laptop screen again and have a quick look at the car.
So this is just a quick pic I snapped yesterday with Ben just about to head out to do some
testing.
The bodywork on it is a little bit rough so we won't focus too much on that but what I did
want to really focus on is the power plant.
This is, as I mentioned, a built K20, it's nothing wild, it's got a ported head, CNC ported head,
a little bit more compression than stock, some better conrods and a set of cams.
Obviously what we can also see here is it is running a set of individual throttle bodies here.
This is specifically a set of Jenvey throttle bodies.
Trumpets obviously hidden there behind that Pipercross filter.
It's all controlled by a Emtron SL4.
One of the problems with this is that the car doesn't run ABS.
I mean obviously nothing particularly unusual about that, ABS is definitely not a pre requisite
for a race car.
This does run a pedal box with adjustable bias as well but given that both Ben and I have come
from a few seasons now of racing cars that have got ABS, you do tend to get a little bit
lazy and start relying on it.
And of course a decent lock up can very quickly destroy a brand new slick which is a significant
investment in cash so we don't want that happening.
So while it hasn't actually been as bad as I'd anticipated, what I did do quickly was
set up a cheap and dirty, basically lock up light on our C127 dash and I just wanted to
go through what was involved.
This is still a work in progress, I was kind of working at this stage with what was available
on the car but we'll just go through this and have a look.
So the car, as we purchased it, did have one single wheel speed sensor on the front left.
So that's what we're looking at here.
It's a little bit crude but I guess at some point it got the job done.
The problem is that the CRX actually never came with wheel speed sensors but a bit of parts
raiding across the other Honda models makes this pretty achievable.
What we can see here though is this sensor chopper wheel I guess you could call it.
It's a modified or cut down ABS sensor ring and one of the things that was a little bit odd
about this is that obviously they've removed some teeth off this wheel, again this is just how
we got the car.
Now they've removed some teeth from the wheel but one thing I did notice is if you
look at the gaps here, so we've got a gap there and then we've got another gap here
and these gaps obviously aren't the same and that's problematic when we want to measure
wheel speed because the period between the adjacent teeth essentially looks like to the ECU
that the wheel speed is increasing and decreasing.
Again not ideal but we're just working with it at the moment.
The other thing is with these sensors, these are a factory style ABS sensor and I imagine a lot of
people have come unstuck, blindly wiring these into their ECU assuming that they're a conventional
variable reluctance or magnetic sensor and then struggled to get a signal out of them.
And they are actually, they're called a magneto resistive sensor.
These will not work if you just wire them into your ECU and treat them like a normal magnetic
sensor, the reason for this is that the pull up in the ECU, the pul up resistor to 5V will not
provide enough current to essentially make these work so typically you need to mess around
with some external pull up resistors to an 8V or 12V source and generally the best idea is to
actually run them on a scope.
We had a quick play with this and I couldn't get a resistor value that gave me a signal that
was usable so what I ended up doing was actually ditching that completely and going
to something we already had on the shelf which was this little guy here, it's a GT101
Hall sensor.
We'll get this under our overhead.
These sensors have been around for a long time, I've used them for trigger inputs which
is arguably maybe not the best use for them.
They're obviously great as well for the likes of wheel speed or drive shaft speed.
Relatively cheap, relatively easy to source and reasonably reliable.
I won't go too deep into it but they do create some problems with missing tooth trigger
discs on crank trigger systems as well so that's why generally it's advisable to sort of
stay away from those for an actual trigger input but for our purposes, should be OK.
This was a bit of a shot in the dark though, the reason for that is, I'll just grab up the
MoTeC data sheet for this, jump across to my laptop screen.
This is the recommendation from MoTeC in order to build a trigger disc that's actually
going to work properly.
So the problem with this is multiple, first of all we can see here that the recommended tooth
height is 5 mm, the recommended thickness of the disc is 6 mm, it has to also be a ferrous
material, it should go without saying but I'll mention it.
And then we have a maximum gap of 2 mm, obviously you can adjust that gap, you want
enough gap that you're not going to risk the tooth actually wiping the sensor out because
obviously there can be a little bit of movement with the likes of the CV so we don't want to be
wiping out sensor out but we need it close enough to actually get a signal and then
lastly is our tooth spacing.
So the problem is that that sensor ring that we had doesn't meet almost any of those
criteria, I've got a spare CV here and I'll just get this under our overhead so we can sort
of see.
This one's actually a bit ugly, it's sort of been garked up a little bit so I don't think this is
probably one that we'll use but first of all, unmodified, obviously we don't have 10 mm
between teeth and if I turn this over, the tooth height obviously really difficult to see but it's
probably no more than about 1 mm.
Having said that, we put the sensor on because it was really easy to do so and ran the car up
and straight away actually had wheel speed so for my purposes, that was good enough.
Ultimately what we're going to be doing is fitting these GT101 sensors to all 4 corners
of the car.
That's going to give us our undriven wheel speeds at the rear, it's going to give us both of our front
wheel speeds as well so that's going to allow us to set up a proper lock up light sequence.
I'm going to dive into that in a moment.
And it's also going to allow us to use traction control in the Emtron if we need to.
It's pretty good in the dry but I imagine it's going to be a bit of a handful in the wet.
Now on the rear, again there's no provision for a wheel speed sensor at all in the EF chassis
so we're kind of making our own here and this, I'll get this under our overhead, this is
just a disc that Brandon drew up using Fusion 360 and we had a local metalwork
company plasma cut it for us.
The plasma cutting's not perfect, it would be nicer to get them laser cut but it's a quick
and dirty option to get these actually onto the car before we race it.
This was acceptable.
So that's going to actually meet all of the criteria for the MoTeC data sheet which obviously is
going to be quite helpful, obviously want the most reliability, you do exactly what the
manufacturer's data sheet actually suggests you should be doing then there's absolutely no
reason you won't get a signal.
Anyway, let's have a look over at our C127 Dash Manager software and I'll just show you what I've
done here.
This is a situation where there's no black and white, what I'm going to show you, this is
definitely not the only way.
And really it's about coming up with the sort of functionality and logic that you want out
of this and then basically thinking through the different ways you can achieve this.
So the C127 has the benefit of having these 3 lights on each side and really what I wanted to
do is use the top and bottom on each side just to indicate locking on obviously a front or a
rear wheel and that means that we still have the shift light module at the top free for the
actual shift process.
So it's going to be easy to see out of the driver's peripheral vision and just a visual cue that yeah
you've actually got a wheel locked.
So the first thing, obviously we need the speed input coming from the Emtron ECU, we've got
these sensors are going to be wired into the Emtron so we've got the control strategies
we can implement in the Emtron for the likes of pit speed limiters and traction control.
But then we're sending that information via a CAN data stream across from the Emtron
to the MoTeC so that's how we get that data in.
And then, I'll show you the really quick and dirty way of doing this, or how I've done this.
So if I go to calculations and we go to user conditions here, this is how we ran the car
yesterday and all I did was create a user condition called lock up left front.
We'll just dive into that.
And this is probably I think about the easiest way of doing it but it does have some drawbacks.
So what we've got is this is the logic that it's going to use and that channel, even though it
is front left, at the moment it is being sent across as a channel called drive speed so
it's not actually drive speed, it's our front left wheel speed.
So what I've got there is if our front left wheel speed is less than or equal to 10 km/h,
and our GPS speed input is greater than or equal to 40 km/h, then our output channel will be true.
And what we've then created is an output channel that I've called lock up LF for left front, pretty
self explanatory.
So the GPS speed here, I've incorporated that, obviously if we just said, our drive speed is
less than or equal to 10 km/h or for that matter 0 km/h, we're going to have that lock up light
active when we're sitting there stationary in the pit which is going to be distracting at best
so what I've done is I've chosen a GPS speed that's going to be lower than the lowest
speed that we'll see out on track so that just gives us a sort of indication, yep we're out
on track.
The other thing we could probably do in here is bring in something like longitudinal G force.
To make sure that the car is breaking.
Or if you've got break pressure or break switch you could use that, again you're seeing here,
there's no one fixed way we can do this.
Now that gives us our output channel which we can then use.
We'll close that down and we'll come up to our functions here and we want to come down to
our shift light module, click on that and I've got the actual shift light and warning lights here.
We don't really need to worry about that, what I've got though is this one here, our
lock up left front.
So if we click on that, you can use the, select the channel that is going to make this
particular shift light strategy active.
Obviously that channel we just created, lock up left front.
And then we can choose whether it's going to be a static or flashing light.
We can choose the colour of that light and then we can choose where abouts on the
shift light module that's going to be.
That's the top left of those 3 on the side.
So that's as simple as it needs to be.
Now there are some downsides with this technique though because it's only really going to indicate a
completely locked up wheel.
And what we're going to find is that initially there'll be some level of under rotation as
the tyre begins to lock so that won't indicate that, if you look at the likes of most competitive
GT3 cars, they will have different colours of lock up warning just to indicate to the driver
how locked the wheel is.
So I'll show you another way we can do this.
But before we do that I'll just dive into some data and show you why there is some
problems with this technique.
So this is just a lap of data here and what I wanted to really highlight was these two
channels which is GPS speed and then our drive speed which is that channel that we've
just been talking about.
Now I will admit that this data for our drive speed is flawed and the reason for that is
twofold.
First of all, we've got those inconsistent tooth gaps which I've already talked about so that's
going to really be playing havoc.
And also as it's currently wired, it's using the existing wiring in the car which is non shielded
which is not really ideal so there's a little bit of noise in here, I'm actually filtering this
channel just to get it usable.
GPS on the other hand looks relatively nice and smooth.
Now everyone sort of would assume that the GPS speed is going to be rock solid and we can rely
on it, that's not always the case, in fact I'd probably go as far as to say that's seldom
the case.
It's going to depend on the GPS antennae you're using, we're using a relatively common 10 Hz
receiver which, as its name implies there, it's only updating 10 times a second or every
10th of a second which particularly if you're doing 200 or 250 km/h, that's quite slow.
So there tends to be a bit of latency in the signal, it can also be affected by the number of
satellites visible.
Particularly in the south of New Zealand, we don't have as many overhead as we may
be in North America for example.
So if we look at this data, we can see that for example in this particular area here,
the GPS and drive speed match.
Probably got a bit of calibration error here by the time we get into this area, they are
departing a little bit but what I wanted to sort of look at here is basically when you're
under brakes, there often can be quite a latency or lag in the GPS speed changing,
it's not very realistic.
And if we look at that particular point here, we've got a difference of about 10 km/h which
is significant.
So what I'm saying here is if you wanted to take the GPS speed and assume that that was
absolutely accurate and base your lock up off that data, you're going to have some really
big problems.
So let's dive into the dash again and we'll have a quick look at this.
So what we'll do is we'll come to calculations and we'll come down to tables this time and
we'll have a look at a 3D table.
I've already set this up so we can sort of see the way we can do this.
With a 3D table, we can choose an X axis and a Y axis and the output, the Z axis of that is going
to be our actual output channel.
So on the X axis we've chosen GPS speed and on the Y axis we've chosen our drive speed.
Remembering again that is our front left wheel speed and then on the right hand side,
we've just chosen, in this case relatively coarse 20 km/h per division break points
for that table.
I'll come to our output, again I've chosen another channel, I've just called it lock up.
It's just a general purpose channel with no decimal places.
So it's going to be going from 0 to 1.
And then our table, so remembering again our X axis over here, this is our GPS speed.
Our Y axis here, this is our left front wheel speed and basically we can fill this in with 0s and 1s.
So if we look at this particular point here, we're at 100 km/h GPS speed and basically
I've said that if my left front wheel speed is 80 km/h or less, so there's that 20 km/h
buffer there which takes into account the error in the GPS or lag, latency, whatever you want
to call it, then we're going to activate that channel.
So essentially we can start bringing on that lock up light before the wheel has actually
completely ceased rotating.
So again, lot of flexibility in how you want to do that depending on your own preferences.
You can bring in multiple stages of this as well with different colours.
Generally I try not to overly complicate things as well, the more the driver needs to remember
and understand on the fly, the more problems you're likely to create for yourself.
So just thought that might be interesting for some of you who are racing cars without ABS
and I've used the MoTeC dash as an example there but you can do this on just about any
quality dash that you're likely to have access to.
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