Jun 112018
 

Ashley, Chairman Essex North Panel, has requested help with the following please:

Remap Essex North have been asked to make a remote stop device for an older Kubota Mini Tractor. The Tractor is used on a Therapy Farm run by a very experienced OT.  Clients are occasionally allowed to drive the tractor once the supervisor is happy they are competent to do so and have had enough training. Currently if anything goes wrong or a dangerous situation arises the supervisor reaches over the drivers leg and pulls the stop control.  Tractor is quite old and diesel powered stopping it is possible only by cutting the fuel achieved by pulling the stop lever, this is common to most older diesel farm equipment. We have been asked to make a remote stop device, the solution we have currently is a cord (extending dog lead?) attached to the control in such a way that pulling it will activate the stop control. However, this solution is not really what is required they really want a completely remote system that the driver is not aware of , I think this is a driver confidence issue.  Remote we take to mean within 20-30M or so with safety person behind or out of direct sight of the driver whist still being able to assess the driving. Tractor is used on level ground albeit quite muddy at times.  We have thought of solenoid valves and car key fobs but all have issues with failing safe.  Has anybody made something like this?  Perhaps  a contact with a University or College could help we are open to any ideas or if you want more information do get in touch.

Thanks

Ashley  essexnorth@remap.info

  14 Responses to “Remote stop device for Kubota mini tractor”

  1. I am a little concerned that the fail-safe aspect of this project has not been clearly defined. One area I can see that could cause problems is that the RF side of things is not being monitored for failure. The scenario I can foresee is that a STOP command from the RF handset (the transmitter if you like) may not be received by the tractor (the receiver) and the tractor would fail to stop! This is clearly sub-optimal 🙂

    The only way to make this fail safe is if the Tx side sends a constant RUN command. Then if the tractor looses that signal…or a STOP command is received, the tractor should then stop. This would then prevent any RF interference/batteries/range etc. from compromising the safety of the system.

    This type of system is often called a charge-pump, or keep-alive.

    Yes it would complicate things a little but a suitable RF Tx module hooked up to an Arduino, could perform the task. On the tractor you would need an Rx module and again an Ardiuino to perform the charge-pump functionality.

    Every time the charge-pump is charged a red lamp could be flashed on the tractor to give a reassuring heart-beat to all around.

    If you need any help with the sourcing/design/programming of such an RF fail-safe device then let me know.

    Roo

    • PS – The RUN command would normally be sent every second or so. The tractor would stop if either it received a STOP command, or if it failed to receive a RUN command for more than say 5 seconds. Obviously these times are completely customizable in the Arduino code and based around risk.

  2. Update Thanks for all the help so far. We think our solution should operate the diesel injector pump stop lever not cut the fuel to the pump, that way we will get a quicker stop. The tractors manual stop operates this lever but has quite a complicated linkage and we will need to leave this is. Place. We have however think we have solved the “ remote” part of the solution.

  3. Thanks for the replies. We had thought about a solenoid valve. I’m not that familiar with diesel pump metering units but we think cutting the fuel should stop the tractor in 2-3 seconds. It’s an old tractor doubt if it has much in the way of electrics just a battery alternator and starter motor, probably had headlights too.
    I’ve passed on the ideas to the engineer involved. One point is that the radio control frequency for model air planes is strictly reserved for models and there are big fines for using the model frequency for non model applications. Remember the Only Fools and Horses sketch where he made a phone call and all the model airplanes crashed! I’m sure this doesn’t apply to door bells or garage door openers.

    • The remote control relays of the type I mentioned are on the 433Mhz band. This is the same spectrum as other low power entry/exit systems, such as car door locks, garage openers etc.

      • Hi Ian. I’m thinking you could wire this up to act like a no volt release contactor so energising a relay causes it to latch on and will stay latched until you open a normally closed switch in the power feed. Should be all thats needed. I like the fuel solenoid with a manual valve the owner could then operate the manual valve for most day to day uses then switch it to remote stop when he wants a client to use it. Remote control devices seem easily available but we need to remember its a tractor witch will vibrate a lot (its a 3 cylinder one and old) get very dusty probably wet and likely to get hot and indeed cold so the receiver will have to be reasonably robust.

        • Yeah – that’s what I meant by using the “normally open” contact on the relay. The circuit has to close it. This means the relay is energised for all the time the engine is running (which will shorten its life*) – but it should fail safe**.

          *One option is to replace the relay on the board for a high quality one rated for continuous duty.

          ** One risk is that if a relay is switching a high power load and/or being overloaded, the contacts could weld together. But I can’t see that being a significant risk in this case.

          Maplin (R.I.P) used to do one of these remote control relay products long before they surfaced widely on ebay. I have one that has been in use for over 10 years. It controls a solenoid that lifts a dead-bolt out of the top of my garage door (keeps thieves out!). So they seem to be pretty reliable.

          But for really challenging applications like this, you have three options.

          1. Conformal coating. I use Electrolube HPA which you just spray onto the circuit to protect it. This is the simplest solution.
          https://en.wikipedia.org/wiki/Conformal_coating

          2. Potting – which is basically encapsulating the circuit in epoxy. I don’t like doing this as you’re stuffed if anything goes wrong + you won’t get the same air flow around the circuit for cooling purposes.

          https://en.wikipedia.org/wiki/Potting_(electronics)

          3. You can get IP67 rated little project boxes. IP67 is protection from dust AND will stand complete immersion in up to 1M of water for 30 mins.

          With options 1 and 2, I tend to do away with any screw terminals and removable links on the board and solder everything.

  4. Wireless doorbell. A valve that’s normally closed which will remain open only if the bell push is operated every couple of seconds, or whatever the response time needs to be. To be fail-safe, it has to have a continuous stream of human-initiated commands in order to continue operation. The electronics at the “bell” end is quite trivial – indeed the typical run-time of the music may actually be just about right for giving the required response time. That output controls a transistor operated solenoid valve via a low pass filter.

    It’s possible to increase the “fail safe” still further by using two valves. One my possibly be used as a bypass valve – “short circuiting” the pump, dropping the fuel pressure to near enough zero. It’s also worth considering replacing a mechanical fuel pump (it the vehicle has one) with an electric fuel pump plus one way valve with a settable minimum operating pressure. No electricity to the pump then equals no fuel supply.

    I spend a lot of time in Norfolk, not that far from Essex and have used wireless door bells for many of these remote control situations – they are very cheap for quite a reasonable range!

  5. To make it failsafe the fuel solenoid should be of the type that requires constant power as suggested but also the remote should be constantly (or at least frequently) transmitting a signal to keep this power applied such that if the remote was dropped in a puddle, got out of range or something else happened to it the system would fail safe to turning off the solenoid.

    There are some simple 433Mhz, and 868Mhz based radio modules, the rest could be handled with an Ardiuno or similar micro-controller.

    • Good point Graham – some of those remote control relays reckon to have a range of 100M, but there might be real-life issues/obstructions which reduce the range and/or there would ideally need to be two remotes trained up to the receiver in case the battery in one fails.

      • It depends if they want true fail safe or just redundancy. Two receivers and two remotes would provide a lot of that but interference that affected both would not cause it to fail safe. Really it requires a risk assessment to decide what is needed realistically.

        Graham

        • Indeed. There are so many variables here and we can’t adequately assess without being there on a project like this.

  6. Member Ian Midgley, addresses the issues concisely, with any loss of remote signal causing fuel shut off, a fail safe system.

    If I may suggest additional safety, with a dual channel garage door controller, ( or two separate single channel ones) with a single fuel solenoid valve, and two individually controlled relays (should be positively guided type) with solenoid coil supplied through two sets of contacts in series.
    Therefore channel 1 controls relay number 1; channel 2 controls relay 2.

    The relays should be mounted to isolate them from any vibration, unless solid state ones are used.
    Machinery directive calls for two individually operated controls for most safety systems.

    You could also add a wrist cord, through plug-in, ref jet ski, if only for a little sense of danger if the clients under supervision are not daunted, or are able to appreciate this feature.

    Riding a tractor sounds a most enjoyable experience.
    Regards.

  7. Hi Ashley – you can get solenoid operated fuel valves for boats/cars, such that fuel only flows when voltage is applied. Examples here.

    https://www.seascrew.com/browse.cfm?FUEL-VALVE-ELECTRIC-12-VOLTS-SHUTOFF-ISOLATOR–SOLENOID-&p=0000006066
    https://www.electricalcarservices.com/anti-theft-solenoid-valve-for-petrol–diesel-fuel-lines-3.5mm-bore/p-2342

    What you could then do is wire the solenoid through the normally open contacts of a remote control relay of the type widely available on ebay. You’d need to test the operating distance for these.

    In both cases, you are applying power to both all the time the tractor is running. If either fails for any reason, it ought to fail safe. But of course, there is no absolute guarantee. Plus if this sits in the fuel line, you would need to consider how long the engine might still run on once the valve has been shut.

    Finally, the power to both needs to be through an ignition controlled feed or it could be left on by accident and drain battery.

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