Engineer Geek Page

Are you tech savvy? This page was created for those of you that understand what our Chief Engineer has to say better than I do! He really is a genius, (but don’t let him know I said that)

 

 

GalgoMoto Strain gauge measurement error strategy:

The heart of the GalgoMoto quick shifter is the strain gauge sensor.  It is waterproof, shockproof and will not weld or fail like simple spring loaded switch sensors.  Most importantly it offers adjustable shift preload over a range of  +/- 2 to 12 Kg, push or pull, that is not offered with spring set shift switches that are prevalent in the industry..without mentioning names..The real issues with strain gauge technology is repeatability; and that is a genuine concern as both temperature of the sensor as well as lead length and individual manufacturing differences can affect overall accuracy.  To get an understanding of the proble, at Galgo we look for the identification of a “shift” to be as low as 50/1000 of a volt!  Think about that!  That is a 4 Kg shift..typical,  and at a 10 Kg shift this represents 120/1000 of a volt.  Because of such small voltages that have to be measured, temperature drift inaccuracies  can be caused by current heating from the actual power applied to the strain gauges as well as ambient temperature changes. 

The normal method of addressing these potential inaccuracies has always been either direct temperature compensation using a temperature detection device mounted on the strain gauge sensor to generate a temp compensation curve or to use a “minus” strain gauge in the position usually reserved in the Wheatstone bridge for a second “positive” strain gauge  that is used to increase sensitivity.

The temp compensation method that depends on a separate temp sensing device adds cost and complexity to the design while the “negative” strain gauge method decreases sensitivity of the unit.

At Galgo we have used the following strategy:

First we use a digitally controlled resistor to put the Wheatstone bridge into an acceptable range of operation when the bike is first turned on based on multiplying the difference voltages by 388.  We call this output voltage from the differential amplifier Vref.  We use the digital resistor to set the useful range of the output to between 2.25v-2.75v.  Once the system has stabilized in this voltage range we cut off the permissive for the digital resistor and let Vref “float” over this range to compensate for minor temperature changes.  A shift command is “recognized” whenever Vref changes by Vref+Increment where “Increment” is approximately 50 mv.   This means that every cycle Vref (every 0.000000006 seconds) Vref is examined for a shift signal and will respond ONLY if a 50 mv or greater increment is detected for over 10ms…  If the temperature at the track drops like 20 degrees or so and the system drifts out of the desired operating range the system will allow the digital resistor to function to return Vref to within bounds and we start from there..but it won’t keep you from freezing!

This method results in repeatable shift preload “shifts” and reduces cost to the customer..We love what we are doing!

Richard King

Chief Engineer for GalgoMoto LLC.

The advantages of auto-cal for strain gauge measurement systems:

Almost all strain gauge measurement systems depend on the Wheatstone Bridge.   The principle for the design is to generate a measurable voltage differential after a very small change in resistance is caused by micro stresses in a material that has been put under load.  Nothing so far has proven more effective or reliable for strain gauge measurement.  The small micro volt differences across the bridge are then amplified 100-200 times by a sensitive solid state amplifier to create a usable signal that is proportional to the stresses placed on the gauge.

One of the main issues with respect to accuracy is the fact that very small resistance differences, as small as one ohm can affect the balance point of the Wheatstone Bridge and throw off its calibration.  In our earlier units we hand balanced the bridge by making micro changes in the balance resistors so that the bridge perfectly matched the two individual strain gauge units as well as the resistance in the lead in cable.  Although this worked ok..it was time consuming and what happens when the customer wants or needs to replace a sensor unit in the field?  What happens over time as the strain gauge off-set eventually changes due to work hardening of the substrate?

A feature that is unique to the industry that GalgoMoto has developed is a strain gauge measuring and amplification system with microprocessor controlled auto-calibration on each and every start-up of the bike.  When you start your bike..the micro-controller adjusts a digitally controlled resistor in the Wheatstone Bridge to bring the bridge into balance.  This system compensates for any small variations in sensors, lead length, temperature, fatigue, wear, etc! And it happens each and every time the unit is turned off then turned on again.  The calibration takes less than a second to complete and completion is indicated by a steady green led light on the front panel of the QS4.1 unit.

In addition to a patent pending sensor design that allows push or pull shifting with NO wiring changes via Bluetooth connection this feature is just another innovation that GalgoMoto brings to the QuickShifter market.  By Riders..For Riders..

Quick Shifters…Understanding the Technology of Quick Shifter Control Systems

Modern Commercially available quick shifters are great additions to any motorcycle.  In fact, some of the newest and most expensive motorcycles come with factory installed systems.  They all allow the motorcycle to be up-shifted at any throttle setting without using the clutch and, if desired, the throttle can be kept fully open to give maximum drive between gear changes.  If you have not used one you will be amazed how effective they are.  Especially on the race track!  ALL professional racers use quick shifters on their motorcycles..it is NOT just bling!

So how do they work?  Quick shifters, upon detecting an impending gear shift at the shift lever, interrupts the output power from the engine for a very short interval.  Typically 60 to 70 milliseconds.  This unloads the shift dogs in the transmission which allows them to disengage from the current gear and slide into position on the next gear selected.  When you use the clutch you do exactly the same thing..but you are out of “power” for a much longer interval.  There are two principle ways to precisely interrupt the engine power, interrupting the fuel flow and interrupting the spark.

At least one very popular unit is sold that interrupts the signal to the fuel injectors on fuel injected engines when a shift is detected.  This works quite well and since this particular unit is often hooked up to allow modifying the fuel curve on the motorcycle anyway, it just requires a sensor and some software to work.  The downside of this technology is that it will NOT work on bikes without fuel injection and it will NOT work on high performance high RPM motorcycles that have two sets of fuel injectors.  These motorcycles have what is called a “shower head” injector mounted up in the air box that sprays down into the throttle body air funnels.  The idea behind the “shower head” injectors is to give the high rpm engine more “time” for the fuel to properly atomize and mix with the incoming air.  This has the unwanted effect of making it impossible to generate a properly timed power interruption because when  the shower head injector is signaled to shut “off” the fuel and air mixture is still traveling down the intake track and there is a delay in the “kill” interval.

The second method to achieve power interruption is much more popular.  It is to simply interrupt the spark and therefore it is not limited to just motorcycles with single injectors or fuel injection period!  This system will work on ANY motorcycle and even your lawn mower if desired.  (Yes we will make one for your lawn mower on special request! LOL!)  There is no downside for this technology..at all..if properly employed using the correct strategies.

So that we can explain the difference in various strategies we first need to explain how a motorcycle ignition system works.  There are two main types of ignition systems used on motorcycles.  The CDI or capacitor discharge ignition system and the much more typical inductive discharge ignition, sometimes called the Kettering ignition system.  Other than some dirt bikes, by far the most common ignition type on motorcycles is the Kettering system so we will only go into the detail on that system.  It is really very simple and works by first charging a coil of wire with a current, thus creating a magnetic field, then suddenly stopping the current flow to the coil of wire which causes the magnetic field to quickly collapse which creates a very high reverse voltage across the coil of wire.  When this coil of wire (the primary) containing “N” turns is wound onto a common magnetic core of steel, iron or ferrite material that has a second coil of wire (the secondary) “N times X turns” of wire on it, a much higher voltage is induced through magnetic coupling on the second set of turns of wire.  This is then connected to the spark plug and makes the spark.  These voltages are typically in the thousands of volts!  So..in a nutshell, all you have to do to make a motorcycle ignition work is to just cause a current to flow in one side of a two coil electro-magnet and then suddenly stop the current just when you want the spark to occur.  Yep it is just that simple.  So how do we make a quick shifter work? First we have to go into just a little more detail..

In a 4 stroke engine the spark plug only has to fire every other revolution, unless the engine is of the “wasted spark” type where the plug fires every revolution.  Wasted spark systems are rare these days but work fine.  The only thing is,  that not only does the spark plug fire at the top of the fuel-air compression stroke but also on the exhaust compression stroke as well.  It just doesn’t DO anything on the exhaust compression stoke but it doesn’t hurt anything.  The reason wasted spark systems were used was to allow one coil to provide spark for TWO cylinders.  The popular Kawasaki ZRX 1200 uses this type of spark system for its 4 cylinder engine.  There are only TWO coils.  The reason I mention this is that this must be taken into account when designing a quick shifter unit. (and our Quick Shifters allow this selection)

Getting back to the actions of the ignition system…there are three main sequential intervals in the life of a spark coil.  Dwell (charging), spark (discharge) and dead time.  All of these intervals must take place, head-to-tail within the time it takes a motorcycle engine to complete two revolutions.  To give you an idea what kind of  time this is, at 10,000 rpm this period is 12/1000’s of a second!  If it were a wasted spark system the interval would be 6/1000’s of a second!  Typically, most modern spark coils require the application of 12 vdc for a period of 5-7 thousandths of a second to store enough of a magnetic field to provide a strong spark and the spark typically is about 2 thousandths of a second.  Thus, in a typical 4 stroke motorcycle engine running at 10,000 rpm the dwell, or charging interval is 7 milliseconds, spark 2 milliseconds leaving a dead time following the spark of 12-7-2= 3 milliseconds.  Stuff is happening quick! Now let’s make it even more complicated.  You might ask yourself “what is the purpose is of the dead time interval?”  I mean..why don’t we just restart the dwell cycle immediately after the spark and simplify the cycle?  Well..actually at very high rpm you could do that with no ill effect but it will NOT work when you sit idling at the stoplight at 1,000 rpm!  At 1,000 rpm the dead time becomes 120-7-2=111 milliseconds.  Modern spark coils are now made with very low resistive impedance on the order of less than one ohm.  Something like 0.6 ohms.  Using ohms law we do a quick calculation and take a typical 13.8 vdc system divided by 0.6 ohms to come up with a current flow of 23 amps!!!!  This would burn up most of the wiring in your system or blow fuses..and will for sure burn up the spark coil.  So how does it not do that during the dwell or charging cycle?  It is due to the principle of inductance and time.  A spark coil is an inductor and, an inductor “looks like” a very, very high resistance when you first start charging it.  As the magnetic field starts building up this resistance is reduced and the charging current continues to increase.  The secret to limiting the total coil charging current to something manageable is to limit the charging interval.  Thus at lower operating rpm there MUST be dead time prior to the next dwell interval or you would burn the hell up everything.  Don’t ask me how I know this for sure..

So why have we gone into all this technical discussion?  So that you understand the difference between quick shifter designs that work at the race track and those that will work anywhere.  The foundation of our GalgoMoto QS 4.0 design is to “detect” the next cylinder( followed by the others in order of the firing sequence) coming into the dead time period and prevent it from starting its next dwell cycle until AFTER the power interruption interval has expired. Then it hands off operation to the motorcycle ECU. This is very important.  This strategy exposes the spark coils to no more than factory specified dwell times and does NOT randomly interrupt the dwell cycle of any cylinder which could result in a partial spark on a charge compression cycle that “could” occur at lower rpm, causing pre-ignition.  Our system “reads” every individual cylinder so that the power interruption interval is optimized without damage to the engine or its components. This is in contrast to some lower cost quick shifter designs, some of which I have designed and used myself!

Years ago I designed a simple quick shifter system for my old (and still my current) SV 650 track bike.  The way this one worked was that whenever the system detected the power interruption signal from the shift lever, it would simply ground the spark coils, essentially putting all of them into the “dwell” interval for a duration of about 65 milliseconds.  This works great at high rpm where there is little chance that the random coming out of dwell point would produce a dangerous pre-ignition spark in the engine.  However it DID expose the spark coils to very high currents in excess of their design during the long “kill” interval! (I learned this two sets of coils later. ) To overcome this issue I had to install current limiting resistors in series with the spark coils to “protect them”.  Problem is this limits the maximum charge amount in the coil at stock dwell times and a somewhat weaker spark.  It works..but it is ugly..and cheap!

So now you understand the basics and intricacies of quick shifter control system design.  You can now go out and build your own and avoid some expensive mistakes or…you can buy a Galgo!