DIY electronic throttle and gearbox control

Discussion in 'OnBoard Electronics & Controls' started by CDK, Apr 3, 2008.

  1. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    Thanks for the links, they may be useful in future.
    For the gear shift you need fwd, neutral and reverse, which cannot be achieve with a 2-pole rocker switch. The circuit with 2 relays and a few diodes was the simplest I could think of. I've also used a more "electronic" circuit but had problems with the large variations in supply voltage.
    For the throttle you need precise control, not just full throttle and idle.
    Although, now that I've mentioned that, some guys don't need anything else...
     
  2. L'eau.Life
    Joined: Jan 2008
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    Location: Bay of Islands, New Zealand

    L'eau.Life Junior Member

    Ahh well, back to the drawing board - I knew my approach had to be too simplistic!
     
  3. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    Hi Fani, read your post yesterday, but it seems to have disappeared now.
    Indeed, they call it rotary encoder. It works opto-electronically, so it should live far longer than a pot. Anyhow, you asked for alternative measuring methods; I also use pots because of simplicity, preferably sealed ones with conductive plastic or wire wound.
    For a digital indicator showing the amount of water in the cistern I used a home made encoder based on the excess-3 Gray code, where there is always just one transition when the number increases/decreases to prevent misreadings caused by mechanical tolerances. I still have some very old ttl decoder circuits like 7443 and 7444 that I used for this purpose.
     
  4. Fanie
    Joined: Oct 2007
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    Location: Colonial "Sick Africa"

    Fanie Fanie

    Hi CDK,

    There are some fancy encoders / movements available, but the price waters one's eyes on those modules.

    The simplest is probably to use a screw and nut where the motor turn the screw and the nut pushes the ie. throttle. If one uses a screw then it should be ok to count turns... on a 6mm thread it is 1mm per turn, four pulses per turn is about 0.25mm, should be acurate enough. To 'home' the movement another switch can be used.

    Hall effect switches works perfect to count revs with, no mechanics, very fast, and super reliable too. Allegro.com have some of these devices.

    There are linear hall effect devices as well. The problem is using them as an adjustment feedback may have some problems with magnetic fields interfering with one another as the throttle and gearshift may be close together.

    It may well be possible using mu-metal, to create a tunnel for each magnetic field to operate in. Mu-metal is used in ie floppy drives to shield magnetic fields from the magnetic memory material. I haven't investigated the distance these linear field hall sensors will work at, but it may be worth a look at.

    One could also of course mount a bunch of these hall switches in a row, and as the movement progresses, the switch corresponding with the magnet's position will be the position indicator.

    I am a bit hessitant to suggest a pot, simply on the grounds of it's mechanical characteristics. Even if it has a good rotational spec, I'm thinking in bad waters you are riding that throttle all the time and in seconds... which if you calculate life span may not be as lengthy as one would expect. I for one is bad on maintaining things, so I'd rather go for the maintenance free option that would last forever - in theory anyway.

    I have in fact started a project with a rotational position feedback using hall switches... just didn't complete it. I may look into it again, it's still on my list of projects.
     
  5. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    Returning from a somewhat longer test run last Sunday, the throttle of the port engine 'froze' at approx 1200 rpm. I removed the throttle cable and returned to our bay with one engine idling. I use the word 'froze' but in fact the reason was the present heat wave and the heat buildup in the engine bay. One of the windshield wiper motors simply fell apart. The plastic housing may survive in a Smart-for-two, life between 2 diesels on a hot afternoon was more than it could handle.
    I am now constructing something totally different with geared industrial motors, a stainless steel screw spindle and a slider pot. This I will mount directly on the injection pump, which is quite a challenge on a vibrating diesel. If it resonates and I can't solve that, I will revert to remote mounting and a short Bowden cable.
    Pics and drawinging I will post as soon as nr 1 is ready.
     
  6. CDK
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    CDK retired engineer

    The prototype is ready for testing!
     

    Attached Files:

  7. Jack Daniels Eq
    Joined: Aug 2008
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    Location: Phuket

    Jack Daniels Eq Shockwave

    Hi - I am currently working on something similar - has anyone done an upgrade that we might take a gander at - would save reinventing the wheel somewhat
    BR>Jack
     
  8. CDK
    Joined: Aug 2007
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    CDK retired engineer

    The device I presented in this thread performed reasonably, but there were a few flaws.
    Engine vibrations, especially near idle, caused rapid wear of the fully extended spindle, so I added a support, made from a plastic with very low friction.

    Because the electronics are linear, the supply current to the motor is gradually reduced when the actuator nears the desired position. Because of differences in friction, caused by temperature and/or dirt, the idle position was not exact. I've added an end limit switch that opens the circuit to the motor when the idle position is chosen a fraction further than required. A diode across the switch allows the spindle to return to open the throttle.

    The previous version could not supply the full 12 VDC to the motor because the opamp's positive voltage swing cannot reach Vcc. I designed a new circuit with an unusual principle: instead of using the output pin of the opamp, the output stage is connected to the + and - supply pins, where the current can vary between the internal consuption (0,2 mA) and the load current (15 mA).
    This way the maximum voltage across the motor is only reduced by the Vce-sat of the output stage. With the diesel engine running, there is approx. 13,6 volts available.
    I also added a simple stabilizer circuit to avoid influences from voltage drops when loads like an anchor winch or bow rudder are switched on.
     

    Attached Files:

  9. farjoe
    Joined: Oct 2003
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    Location: med

    farjoe Senior Member

    Nice project CDK?

    For us electronic geeks it is putting together the mechanical side which stumps us, or at least me.

    Could you tell us more about your motor movement assembly? Did you buy it off the shelf or did you get it machined?

    thanks
     
  10. CDK
    Joined: Aug 2007
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    CDK retired engineer

    All mechanical parts I made myself. My favorite tool was and is a soldering iron, but for projects like this I have a lathe, metal band saw, plasma cutter, TIG welding machine, table drill and lots of hand tools.
    www.firgelliauto.com makes a better looking product for approx. $ 100, but for me the fun is in making things, not buying them.
     
  11. Jack Daniels Eq
    Joined: Aug 2008
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    Location: Phuket

    Jack Daniels Eq Shockwave

    This gets confusing - received an email alert of a CDK reply - Gracias - but cannot find it here - the latest I show is March 04 - it is March 20 - or is it because I use Linux#$%^& - I have ordered some inexpensive [$80] automobile cruise control bits to play with - like my big BMW they all run pretty decent CC - an auto engine compartment is a pretty brutal location to mount anything, so am hoping to get out of jail free here - at least not reinvent the wheel every second day - will revert - I also need input on my big boat automation project - all help appreciated
    BR>Jack
     
  12. pcguysam
    Joined: Jun 2009
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    Location: Dallas, TX

    pcguysam New Member

    Nice Work CDK! I am truly impressed. As I quit EE school because of circuits, I could use your assistance. My project is the same as yours but I am approaching it this way:

    Separate actuators with POT feedback purchased from Firgelli for the trottle and gearing.

    What I need is a comparative circuit that can keep the actuator and control handle in sync. The POT in the actuator is a 10K, so I was going to use the same in the control handle. Basically, I need a circuit to supply +12V to the actuator if the actuator POT is LESS than the control POT. And it needs to supply -12V if it is MORE than the control POT. If they are equal, then it should do nothing.

    Now, in programming, this would be easy with an if/then statement. I am not sure how this is done with circuitry. Please help!

    Oh and my boat is a 28' Pontoon Barge that I rebuilt from the deck up. It is powered by a 1982 115HP Johnson. My mechanical throttle control box seized up while I was on the lake Sunday. I decided to try a different solution to replacement of obviously flawed technology.
     
  13. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    That is exactly what the circuit in post #38 does.
    For the control handle you can use other values than 10K; if you want the resistance on both sides to be equal, use 20K with both end terminals tied together to get 10K when the wiper is in mid-position.

    I also ordered 2 actuators from Firgelli yesterday to keep as spare parts in case my own handwork gets tired. I will experiment with the existing circuitry when they arrive, probably just the resistor values in series with the POT must be changed a bit.
     
  14. MattZ
    Joined: Aug 2005
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    Location: British Columbia, Canada

    MattZ Junior Member

    Did you have any oscillation trouble with your electronic throttle control? (i.e. when the throttle position command was held constant, did the control motor oscillate back and forth?)
     

  15. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    No, there is none.
    But it could happen if the mechanical parts have little friction and/or a large mass. I purchased a pair of linear actuators from Firgelli and noticed that they tend to overshoot the target sometimes, especially when throttling back because the spring on the injection pump lever is quite strong.
    The problem can be solved by using lower feedback resistors.
     
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