Locomotive electronics & switching

Discussion in 'The Projects Forum' started by mrpotatohead14, Dec 16, 2014.

  1. mrpotatohead14

    Thread Starter New Member

    Dec 15, 2014
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    Hello everyone
    Please can you help I am an absolute beginner when it comes to electronics. I am about to venture off building what in essence is a ride on electric locomotive. But no one other than a mannequin will be riding on it and it will be very simple in design and will traverse up and down a straight length of track, it will be driven by an electric 12v motor and powered by a 12v car battery but my problem is I need to stop it at each end of the track and send it off in the opposite direction. so it just goes backwards then forwards, I have preconceived ideas of two motors and limit switches can anyone put me straight
    Any help will be greatly appreciated
    Thank you
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    just put a couple of two way switches at each end of the track, then when the train hits the switch it reverses the battery connection using a DPDT relay, and the train runs in the other direction.
     
    Last edited: Dec 16, 2014
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  3. mrpotatohead14

    Thread Starter New Member

    Dec 15, 2014
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    thank you does it matter that the switches would have to be mounted on the loco as the track is all timber ?
     
  4. crutschow

    Expert

    Mar 14, 2008
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    If you have a reversible motor then you only need one motor.
     
  5. crutschow

    Expert

    Mar 14, 2008
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    On the loco would be the preferred location for the switches since that's where the motor and circuitry are.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I would think you need a little deceleration if there is any kind of weight or significant load on the motor. Especially if there is physical end stop (buffers)?
    Also a pause instead of instant reversal, which will certainly drain the battery.
    A couple of ways would be either to place a pre stop switch and go into a decel rate, alternatively let it coast, if precise stop is not needed, Do you have the motor yet?
    Max.
     
  7. mrpotatohead14

    Thread Starter New Member

    Dec 15, 2014
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    No I have not chosen one yet
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    What kind of mass (weight) are we talking and estimated speed of the Loco?
    Max.
     
  9. mrpotatohead14

    Thread Starter New Member

    Dec 15, 2014
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    I think a 100kg should cover it I want it to run slowly say walking pace it will be running on the flat no climbs or gradients !
     
  10. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    If the battery is on the loco with the motor, then use one two way slide switch under the loco, and a block at each end of the track ,so when the train hits the block it pushes the switch and reverses.
     
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  11. mrpotatohead14

    Thread Starter New Member

    Dec 15, 2014
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    sounds good I will start to look for slide switches on the net I am extremely greatful I can not believe how helpful you all are
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
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    So you probably require decel and no instant reversal, or some way of a brief pause before reversing would be in order?
    Instant reversal will shorten the charge life and reduce the ability for continuous service, and if the traverse length is short, could overheat the motor.
    Max.
     
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  13. mrpotatohead14

    Thread Starter New Member

    Dec 15, 2014
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    thanks max I will have to have a read back through all this and make notes my brain is fried ! you guys are fantastic the one thing I can say is that the locos I have looked at seemed to have a 130w 12v motor mounted in the wheel bogies driving Delrin gears
    thanks Sir !
     
  14. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You may want to look at a truck bumper winch, these usually have the necessary gearing on them and should be easily adaptable for this purpose.
    Max.
     
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  15. mrpotatohead14

    Thread Starter New Member

    Dec 15, 2014
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    think traverse was about 10m 30 feet imperial !
     
  16. mrpotatohead14

    Thread Starter New Member

    Dec 15, 2014
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    nice one I will look at that as there are a lot of guys locally who are involved in the 4 wheel drive off road scene
     
  17. tcmtech

    Well-Known Member

    Nov 4, 2013
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    I think the truck winch system would be total overkill. At walking speed carrying ~100 Kg any off the shelf or salvaged electric bike or kids scooter motor would be more than sufficient once the gearing was set up right.

    Also if it used a 24 or 36 volt motor rated for a normal 250 - 300+ watts running at a 12 volt input it would have no problems at all doing a full reverse under load. If it was a concern a good .2 - .5 ohm 50 w power resistor in series with the motor would drastically reduce the peak amp draw when reversing occurs.

    Switch wise at those low of voltages and power levels most any heavy duty DPDT toggle or similar switch would work just fine. If it was me I would be looking at the local hardware store at a 20+ amp rated four way lighting switch being one of those is basically a DPDT switch in a four wire design already set up to reverse input to output polarity when flipped.
     
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  18. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I can get one of the smaller 12v bumper winches from a local supplier with a P.M. motor and 153:1 planetary reduction for CAN$70.00. it is more than adequate, but the current is only going to be whatever the load demands which should be much less than it is capable of, also any switch or relay you get, make sure it is DC inductive load rated, or the contact life will be extremely short.
    Max.
     
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  19. mrpotatohead14

    Thread Starter New Member

    Dec 15, 2014
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    Thank you for your help up to now !
     
  20. mrpotatohead14

    Thread Starter New Member

    Dec 15, 2014
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    Thank you for your help up to now
     
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