quilkin

Motorising for exhibition

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I built this model earlier this year. It has some Technic elements, including a motor, to animate it. It's now been shown at a one-day exhibition and created quite a bit of interest.

I've now been asked if it's possible for a semi-permanent display at the site of the building on which it's modelled. It would be protected by a screen / glass case of some kind.

At the moment it's powered by a Lego 9v 'medium' motor and a Lego battery box, with removable batteries. At the one-day event I manually started and stopped the mechanism to demonstrate to people as they passed by (i.e. I was present at all times). I also had a supply of spare batteries! But for a more permanent exhibition, where I won't be present, it needs a different arrangement. So, some questions:

  • If I can arrange a suitable mains power supply, rather than a battery box, is the 9V motor up to the task of running several times  a day for 6 months? (I think it would be started by a push-button, and run for perhaps 10 seconds at a time - I can cope with the control for this)
  • If not, can anyone suggest a suitable motor that is compatible with Lego as far as possible (i.e. mounting it and fitting a gear to the output shaft). The workload required is very small.
  • At present the drive is taken through a couple of universal joints and some speed-reduction gears. Should I glue the joints onto the axles for greater reliability? Any other reinforcements suggested?

Rather than looking through the original thread you can see a video of the model working here.

I'd be grateful for responses from anyone who's built working models for long-term performance before. Thanks.

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For long run times the other issue you will have is the ware of the plastic parts against each other 

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Yes I would recommend some lubrication, like maybe some good silicone grease on ALL moving parts, all rotating axles, pivots and pins as well as inside the motors internal planetary gear reduction. This will reduce wear as well as decrease the load on the motor.

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As kieran said, one of the biggest problem in a long lasting exhibition model is the wear of the parts, is a very common issue in GBC's and trains, you could put a little bit of lubricant oil in the functional parts to avoid most of the wearing, about the motor, if it is supposed to be running for a very long time, you could try to use the controller that LvdH said, i think is this one:

il_570xN.729009844_by3g.jpg

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You could attach a timer to the 9V train speed controller so that it only runs during certain times of the day.  I think you can also get programmable count down timers where some presses a button and it run for a certain amount of time.  Or build something that triggers it when someone is standing in front of the display. 

I use silicone lube on my GBCs.  I still get some wear and tear on the plastic, less than without lube.  At some point, parts will need to be replaced.  :classic:

 

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Nice engine/pump house. I would suggest that you have very little motion compared to many GBCs and the speeds of rotation are quite low. At 10 seconds run per flick of a switch, i would be very surprised if it didn't last 6 months, even without lubrication.

even at 60 requests per day and 5 days a week, you're looking at a total run-time of 21 hours over the six months, which isn't that hard for a GBC to rack up in a weekend at a show, and this isn't very stressful motion.

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Thanks for all the responses. It'll be easy enough to add silicone grease to the moving parts. Nobody seems to think the motor isn't up to the task, so that's good - I'll leave it as it is and have a replacement ready if required.

10 hours ago, bonox said:

even at 60 requests per day and 5 days a week, you're looking at a total run-time of 21 hours over the six months, which isn't that hard for a GBC to rack up in a weekend at a show, and this isn't very stressful motion.

That's a great comparison. I won't need to worry too much then.

Quote

What you could do is using and old train controller, which can make it go faster or slower (or turn it off), and can never run out of batteries because it doesn't use them

Puzzled by this, does that controller run straight off a 12V supply then? The engine needs to run at a constant speed to be realistic, although it does reverse now and again: The real one was used to power a lift for carrying ore to the surface. I've yet to build the left mechanism; simulating an underground mineshaft with a Lego model could be interesting.....

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actually the input says 9-12 volt, so you can provide 12V input if you want to (from a wall transformer for example).

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You have a couple of options, depending on how pure you want to be.

If you're up for a little modification and have some skills with a soldering iron, it isn't too hard to hotwire the battery box so that you can power it from a wall transformer. It is even possible to do this while retaining the ability to use batteries (but don't plug it in to the wall if there are batteries in it!).

As others have mentioned, the train controller is also a good solution, with the advantage of not having to make any modifications. They're pretty generous with what they'll accept as an input - they have an onboard bridge rectifier, so AC or DC both work, at 9-12 volts (in fact, I think that the circuitry can handle higher voltages than even that, but I don't recall the details, so I'm not going to put a number on the upper limit). I'd suggest 12 volts though, because there's some voltage drop in the circuitry, so if you put 12V in you get 9V out, but if you put 9V in you only get up to ~8V out. I say "up to" because the controller can also output lower voltages by setting the big yellow dial to anything other than full-lock either way.

 

Hope this helps.

Owen.

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Thanks. I think I'm Ok with the electrics / control side of things, assuming I can use a standard 9V motor. I'll probably build a control system using an Arduino, with just a simple push-button to set the thing going forward for 30 seconds, slow down then reverse for 30 seconds, then  stop automatically  (I'll need microswitches on the lift mechanism to prevent over-runs). My post was more about the mechanical side of things. I queried LvdH's post earlier about the train controller because it said it didn't use batteries, but didn't say what it did use!

The battery box and  train controller don't really help because they offer a manual way of controlling the direction & speed: this would be courting disaster in a public exhibition! A microswitch would prevent an overrun, but then how would it start again (without some additional control logic anyway)?

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If you want to go all LEGO, you could get one of the old Control Center controllers.  It can be powered from wall power and can be programmed to do simple things like run for 30 seconds, pause, then go back for 30 seconds.  For public interface, you could have an external lever that reaches through the display and pushes "play" on the Control Center.  You don't need microswitches if you use clutch gears to allow free spin once you hit the stops.

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49 minutes ago, Blakbird said:

If you want to go all LEGO, you could get one of the old Control Center controllers..... 

That sounds interesting. Clutch gears may be a bit tricky; the lifts themselves were driven via steel ropes (will be Lego cord or similar in the model) from the winding drum outside the engine house. One lift wold be going up while the other goes down (cords wound opposite ways round the drums) . I'd have to use the clutches to spin when the cord tension was too high (i.e. the list reaches the top of its travel). But actually, now I think about it more, a clutch would also prevent problems due to potential snagging elsewhere.

Anyone know if there's a specification for the Control Center anywhere I can download, before I decide to buy one?

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I don't think there is a spec.  It just records your actions and then replays them.

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About the only thing I can recommend is to avoid worm gears if at all possible - worm gears will slide back and forth on their axle and grind up against their mount, causing it to wear away very quickly.

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18 hours ago, Blakbird said:

I don't think there is a spec.  It just records your actions and then replays them.

Ok, perhaps I should be more specific. Does it remember the actions after a power-down (i.e. if mains power is removed?). In this respect one of the Mindstorms bricks would suffice but AFAIK they all run from batteries rather than mains converters.

I imagine it has the older-style connecting cables, so I'd need to solder up a converter cable.

 

18 hours ago, Phoxtane said:

About the only thing I can recommend is to avoid worm gears if at all possible - worm gears will slide back and forth on their axle and grind up against their mount, causing it to wear away very quickly.

Good point. I'll need to change that then, but it means more gears to get a  low enough speed, and space is at a bit of a premium (the motor and gearing is housed under the floor of the building). The next challenge!

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Maybe you could use an XL motor to power it, as it has higher torque/lower RPM, so less wear on the internal planetary gearing for the motor. Maybe for powering it you could just have a simple open terminal push button, basically if people want to see it operate, they hold the button, as soon as they release it will stop. Maybe some sort of simple timer program for an Ardunio could work, with a button. Another thought is maybe a toggleable switch with some sort of mechanical timer, if you had a high gear reduction, just use a flag on it to set off a tensioned reset switch, then it would reset, say after 10 turns off of the output. It would behave similar to a NOR latch with a reset timer, basically one input would stay on permanently, until a timer sends a signal to the opposite side to toggle the switch back to the open position.

You could have some sort of brick built housing attached with the switch encased, and a brick built button that has a catch on one side. It locks down when pushed on, and when the flag rotates around enough times, it will release a catch that will release the button to it's open state, with a spring to assist the button upwards. Basically when the button is down, power is being provided through a PF switch, and when it's up then no power is being provided..

Edited by Tommy Styrvoky

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3 hours ago, quilkin said:

Ok, perhaps I should be more specific. Does it remember the actions after a power-down (i.e. if mains power is removed?). In this respect one of the Mindstorms bricks would suffice but AFAIK they all run from batteries rather than mains converters.

Yes, it remembers the program indefinitely until you over-write it.  If you want to be extra sure, you could also put batteries in it.  It won't use the batteries if it is plugged in, but it would guarantee you'd always have the memory.

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On 11/29/2016 at 0:04 AM, Phoxtane said:

About the only thing I can recommend is to avoid worm gears if at all possible - worm gears will slide back and forth on their axle and grind up against their mount, causing it to wear away very quickly.

I have worm gears in most of my GBC modules.  I use bushings to keep them from sliding around.  That and lubrication seem to help with noticeable wear and tear.

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