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Hi guys I have been working on a lift for my Atlas bridge. Everything is free and used, except the bridge. I have a couple of picture to share, but please remember its still a work in progress. Big thanks to Gilly, Stan2004, NYC, Subway John, RTR, and a very big thinks to Big_Boy_4005 Elliot for supplying the limit switched. Without you all I would have been lost! Here are the pictures the first one is the mock up.DSC00276DSC00277DSC00278DSC00279DSC00280DSC00281

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Last edited by mike g.
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Hi Mark, I am also thinking about adding a counter weight and a gas cylinder to help the down word speed.

Hi Carl, I'm not sure how much I am giving up on the aisle, but the bridge is 40" long and my door is only 32" so it should give me enough to get in and out. I will check how much and let you know.

Hi Everyone, I know its been a while since my last post. But I have been trying to work things out. I talked to Susan about her lift bridge to try and get some ideas, now I am ask you all. I got the up motion figured out some what. But I have a small problem with the down speed. All the electrical is from a kids car like this.carI used the switches for forward and reverse for up and down, the power switch as is, and the gas pedal to put power to everything. Here is a shot video of it in the works. Any ideas would be great about slowing it down on the down word stroke. I tried gas shocks like Susan, Screen door closers, reducing the power, but then the motor doesn't want to move.

I used the rear axel and drive motor from the car to run the cable as the drill did not have enough braking power to hold the bridge once it started down. I can take a picture of that if anyone is interested.

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Last edited by mike g.

I hate to be a broken record, but I honestly think that you should try an electric screwdriver. For this application, you need high torque/low speed. This is exactly what screwdrivers are designed for. They contain the same kind of DC can motors that your car probably has, just geared way down. I'm not sure, but I bet that if you connected one to the same motor controller that you are using now, it might just work. If not, you can find very cheap PCM fan-speed controllers on eBay that almost certainly would work.

Here's my take on the "problem".  Are you applying a constant voltage?  If so, you are victim of the speed-torque relationship.  For raising, load torque decreases (fighting gravity hardest at the bottom) and it appears the angular speed increases near the top.  Conversely, for lowering, load decreases (gravity assist is greatest at the bottom) and it appears the angular speed increases near the bottom.  Some options are:

1. increase the motor gearing (electric screwdriver mechanism?) which makes the torque vs. speed relationship "stiffer" meaning the speed change less with load torque variations for a given motor voltage.

2. design some kind of mechanical counter-balancing system to present a constant load torque somewhat independent of bridge angle.  then for a constant voltage, the bridge would rise/fall at a constant rate.  you would apply a different voltage for raising and lowering.

3. install a motor speed controller.  this is not just a so-called PWM motor controller though a true speed controller will undoubtedly have a PWM controller in it.  all our speed-controlled train engines have this capability.  a speed controller for a DC can motor does not need a tach for speed sensing - the DCC speed controllers in HO and G-gauge engines measure the internal motor parameters (so-called back-emf voltage) to measure speed.

options 1 and 2 will make it smoother but might have the problem of initially getting started for really slow speeds.  electronics can kick-start the motor applying a boost to get things moving but implementing such a circuit might not be in your comfort zone.  from the bouncing of the bridge when you stop, it seems you need to go slower than the video but as you say there is the kick-start problem.  the advantage of option 3 is it takes care of all this - applying the necessary voltage independent of load torque including the kick-start to get it going. 

the components for a DC can-motor speed controller are not expensive...maybe $10 for something that can power your bridge motor.  the problem is i don't know if they sell one packaged in a configuration easily applied to your situation.  that is, speed controllers are usually part of a system like an engine module that also controls lights, sound, smoke and communicates with a command-control system.  i haven't looked on eBay - i'm always amazed at what you can find!

Last edited by stan2004

Mike,

That's what is missing, the speed control. I have two of those vehicles for the grandchildren and had them for the children years ago. They don't seem to have much throttle control.

The counterweights would need to be about 130lbs on each side. The cars typically weigh about 50-65lbs and they are rated for 50-65lb rider, sometimes, 2 riders.

something like this Stan? motor speed controller

Avanti posted:

I hate to be a broken record, but I honestly think that you should try an electric screwdriver. For this application, you need high torque/low speed. This is exactly what screwdrivers are designed for. They contain the same kind of DC can motors that your car probably has, just geared way down. I'm not sure, but I bet that if you connected one to the same motor controller that you are using now, it might just work. If not, you can find very cheap PCM fan-speed controllers on eBay that almost certainly would work.

Hi Pete, I tried 2 different battery screwdrivers, one a Dewalt and the other a Craftsman. Both worked fine lifting the bridge, but both did not have the breaking power to hold the bridge when going in the down direction. That's why I went with the drive motor from the little car with the gears, rear axel, it works great taking it up and ok letting it down, I just want it to go slower and land softer.

Moonman posted:

Mike,

That's what is missing, the speed control. I have two of those vehicles for the grandchildren and had them for the children years ago. They don't seem to have much throttle control.

The counterweights would need to be about 130lbs on each side. The cars typically weigh about 50-65lbs and they are rated for 50-65lb rider, sometimes, 2 riders.

something like this Stan? motor speed controller

I see what you guys are saying about a speed controller, my question is would I have to adjust it for everytime I wanted to go up or down?

As far a counter weight I was wondering if something like a heavy duty spring or maybe even a bungee cord would work?

mike g. posted:
Moonman posted:

Mike,

That's what is missing, the speed control. I have two of those vehicles for the grandchildren and had them for the children years ago. They don't seem to have much throttle control.

The counterweights would need to be about 130lbs on each side. The cars typically weigh about 50-65lbs and they are rated for 50-65lb rider, sometimes, 2 riders.

something like this Stan? motor speed controller

I see what you guys are saying about a speed controller, my question is would I have to adjust it for everytime I wanted to go up or down?

As far a counter weight I was wondering if something like a heavy duty spring or maybe even a bungee cord would work?

I am guessing that once you find the sweet spot it's full throttle on the pedal. When they are driving the cars, once the motor overcomes the starting load it runs full speed or it's off. For a light child, it's like a dragster launch. I don't think adding weights would help. It would be slower at first and then move quickly.

 

banjoflyer posted:
mike g. posted:

Hi Mark, how did you figure out the amount of counter weight?

 

Hi Mike, I just noticed I had not seen this question. Since your bridge is tethered at one end by means of a hinge (I'm guessing) I would start with 1/2 of the bridges weight as a beginning point for a counterweight. A small pulley on either side of the hinged end of the bridge would allow  weighted cables attached to the mid-point of the bridge to slow the bridges descent.

Kinda like this:

bridge

Mark

Shouldn't the cables need to pass through a pulley that would be above where you have it shown on your sketch ?

How about increasing the gear ratio so the bridge doesn't have the possibility to go as fast in one direction.  For speed control, there may already be something that exists, how about using the ERR Cruise Commander to control the bridge?  It already has the back-EMF speed control build in.  Finally, I think Stan's idea of the counterweight is a good one to balance the loads going up and down.

Moonman posted:
 
...something like this Stan? motor speed controller

s-l500

This is "just" a PWM controller.  It does not perform constant-speed control.  I guess it's semantics.  Yes, it does control motor speed as you turn the knob, but at a given setting if the load torque increases the motor speed decreases.  This also suffers from the kick-start problem; even if you found a setting that works for raising, I'm fairly certain you'd have to initially bump the knob clockwise for a second or two to get the mechanism started. 

As for counter-balancing schemes or what I called option 2, this is a slightly different problem than a vertical lift-bridge.  In that case the torque presented to a lift motor is relatively constant throughout the travel.  So a "simple" pulley-weight works fine.  In the angled-lift mechanism, the torque varies since gravity's effect on the moment-arm (or whatever the mechanical terminology) changes with the angle.  You can "hear" this in the video when the bridge lifts; the motor speeds up near the top and you can hear the pitch/whine of the motor transmission increase.  I may be mis-understanding the proposed pulley mechanism, but I think it would take a more complex counter-balance to present a constant-load torque irrespective of bridge angle.

 

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mike g. posted:

So let me ask you this Carl, would the speed controller be wired in between the pedal and the motor? And back to my other question, would I have to adjust it for both directions?

That's how I would try it, Mike. it looked pretty nifty watching you use the pedal in the video. Set the knob and step on the pedal fully. The other option is to just turn the knob and leave out the pedal.

I did see some scooter and electric bicycle controllers and a twist throttle for about $50. They had too many plugs on the controller for other connections.

The electric go kart controllers are around $350 and complex, in that they step in multiple batteries. That didn't even include the throttle!

stan2004 posted:
Moonman posted:
 
...something like this Stan? motor speed controller

s-l500

This is "just" a PWM controller.  It does not perform constant-speed control.  I guess it's semantics.  Yes, it does control motor speed as you turn the knob, but at a given setting if the load torque increases the motor speed decreases.  This also suffers from the kick-start problem; even if you found a setting that works for raising, I'm fairly certain you'd have to initially bump the knob clockwise for a second or two to get the mechanism started. 

As for counter-balancing schemes or what I called option 2, this is a slightly different problem than a vertical lift-bridge.  In that case the torque presented to a lift motor is relatively constant throughout the travel.  So a "simple" pulley-weight works fine.  In the angled-lift mechanism, the torque varies since gravity's effect on the moment-arm (or whatever the mechanical terminology) changes with the angle.  You can "hear" this in the video when the bridge lifts; the motor speeds up near the top and you can hear the pitch/whine of the motor transmission increase.  I may be mis-understanding the proposed pulley mechanism, but I think it would take a more complex counter-balance to present a constant-load torque irrespective of bridge angle.

 

Thanks, Stan. I should have known that would be too easy.

If the electronics options (lots of techno mumbo-jumbo) is not in your comfort zone I'd think there are some mechanisms out there...most likely from the automotive world...that should be adaptable.  For example, it seems a similar mechanism is the motorized-hinged tail-gate lift on a mini-van...or the motorized-hinged gull-wing doors on fancy cars.   Varying torque is required to lift the gate or door (at constant speed) depending on angle.  Likewise, varying torque (and less of it thanks to gravity) is required to lower the gate or door (at constant speed) depending on the angle.  Obviously, in the automotive mechanism, the use of heavy counter-weights is not an option since that would add to vehicle weight.  I can imagine these might be an application for linear-actuator motors as suggested earlier.  In other words this is option 1 of finding a different motor gear/transmission that is stiffer in that speed variations are demoted in the presence of varying load torque.

The reason I asked earlier about the Bascule bridge, is that it's the most common way of lifting an end pivoted bridge in the proto world.  If you counter balance the bridge, it will take a miniscule amount of effort to raise it.  Lowering it will also be easily controlled.  Think of it like a see-saw or teeter-totter.  Give it a few grams of positive down force and you will be able to raise and lower it with a tiny motor.

Even a model airplane servo.

The pulley idea won't work unless it located away from the pivot point of the bridge. 

Extend the plane of the bridge past the pivot and add weight until the bridge is slightly down heavy. 

You say the bridge is 40" long.  Approximately how many pounds does it weigh? 

Don't mean to insult anyone but basic high-school physics will ballpark the maximum (worst case) pounds the linear actuator must deliver to raise the bridge (starting from horizontal).  Since travel of the linear actuator is less than 1 foot, you would presumably couple the linear-actuator a relatively small distance (also less than 1 foot) from the pivot point. 

I'd think 200 lbs is more than adequate (no counter-weights needed) but why not measure-twice, cut-once.  Doing the math might also suggest you only need, say, a 6" rather than 10" travel though it doesn't seem there is a gross cost penalty to buy the longer versions.

I'd consider at least the simple counterweight, that would remove a fair amount of the effort to raise and lower the bridge and give it some balance.  If it was balanced at the half-way point, you'd have a lot less effort to raise and lower the bridge than without the weight.  It's not only the effort to raise the bridge, but the strain imposed on mounting points for your lift mechanism.  You may have plenty of power to raise and lower the bridge, but a mount might bust loose.

MaxSouthOz posted:

The reason I asked earlier about the Bascule bridge, is that it's the most common way of lifting an end pivoted bridge in the proto world.  If you counter balance the bridge, it will take a miniscule amount of effort to raise it.  Lowering it will also be easily controlled.  Think of it like a see-saw or teeter-totter.  Give it a few grams of positive down force and you will be able to raise and lower it with a tiny motor.

Even a model airplane servo.

The pulley idea won't work unless it located away from the pivot point of the bridge. 

Extend the plane of the bridge past the pivot and add weight until the bridge is slightly down heavy. 

That's what I thought.  I posted the same question to Banjoflyer.  Scroll up a few posts to the diagram.  

Hi all, thank you to everyone for there input. Here is what I came up with, I poured a counter balance to attach to the back part of the bridge just past the pivot point. its 7"W X 9"LX 31/2" thick. I am not sure what the weight will be but its more then that's there now. I also ordered the 10" Linear-Actuator just because they are out of 6" and 8".

I am not sure what the bridge weights cause I didn't right it down like a fool. Stan if I just use a DPDT switch I would wire the limit switches just as before correct?

As far as the pivot point there are sealed bearings on each side.

stan2004 posted:
mike g. posted:
...Stan if I just use a DPDT switch I would wire the limit switches just as before correct?
I assume you are referring to your earlier thread about where/how to connect limit switches.  Correct, nothing changes from before.  From an electrical/wiring perspective the linear-actuator is just a DC motor as before.
 
dpdt%20bridge%20drive%20with%20limit%20switches

 

Thanks Stan, when the actuator arrives next week I will post some updated pictures.

Hi Guys and Gals, Here is a little update. I have been working on the bridge and got my Linear-Activator installed. Here is the deal, I need some help to figure out placement of it so it will open to and 90 degree and still   close all the way. here is a video of what I have sofar. Any help would be great!

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The first thing I thought was "why did he put the actuator on that side of the pivot point?"  So even if you could rotate the bridge to full vertical you'd have the actuator sticking out in the aisle which will catch on your belt, shirt, whatever as you walk by.  So I guess my first question is to ask if there's some reason you can't (or don't want to) put the actuator on the right side of the pivot?

I know you forgot to write down the bridge weight, but let's just say it weighs 10 lbs and assume (for the sake of discussion) that this is evenly distributed across the bridge).  From high school physics this is equivalent to a 10 lbs weight sitting about 24" from the pivot point.  So if your actuator can drive 200 lbs, this means you can theoretically raise/lower the bridge by applying the actuator 200/10=20 times closer to the pivot point on the right side of the pivot...or just a few inches away from the pivot. 

Since you "only" have a 10" linear travel, I think you need to use this 20x leverage to allow you to swing the bridge the full 90 degrees (ignoring whether or not real bridges swing to true vertical!).

No, the actuator can be attached to bridge close to the pivot point on the bottom. It has enough power to push it up from there and stay out of aisle.

That looks really slick, Mike!

Mount the actuator base on a cross member attached to the rear outside edge of the stand/base. That will move it back, mostly out of the aisle.

Then fit the height position with the actuator nearly fully extended and the bridge held in a 90° vertical position. Attach the bridge mount near the pivot and the base will mount where it's located/falls. That's where the mounting cross member will need to be.

I think the grandchildren will be playing with the bridge a lot.

Hi all,

Stan the reason I didn't put it on the right side to pull it down is I also made a counter weight for it and was going to mount it there.  But it sounds like you and Carl are thinking the same thing.

Carl, I will try putting the actiuator a few inches from the pivot point and see how it goes. I will take some pictures as I go along and another video when I am done.

Hi All, Thanks for everyone's help I think I have got it almost where I want it. Tomorrow I will adjust the up limit switch, wrap the wiring, and be happy!! I hope you all like it.

Special thanks to Elliot for the limit switches,

Stan for the wire diagram,

Carl for his idea of moving the pivot point.

Gunrunner John for the idea for a counter Balance, wish I could have used the one I poured. But it would hit the actuator.

I am always open for input and ideas!

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Thanks Carl,

I did try it on the back side and between the support legs, but when I raise the bridge the tail end would hit the actuator. The location where it is should be ok, as that part of the bridge support will be behind the wall on one side of the door entering the room. The Bridge is 40" long and my door opening is 32" so that means 8" will be out of the path entering the room.

Not sure, but plumbing supply houses used to sell lead in five pound increments.  I don't see any reason why they wouldn't still have the lead.  Plumbers use the lead to seal pipe joints in cast iron pipe.  For those not familiar with the method, it goes like this.  Basically you have a propane tank, not too different from the barbecue type.  On top of the tank there sits a burner mechanism with it's propane supply hose connected to the tank.  On top of the burner sits a kettle.  The lead ingot was placed in the kettle and heated until it is molten.  Then the plumber dips a ladle into the molten lead and pours it into the pipe joint.  

Bottom line here, Mike, is that the lead ingots are roughly a 3" square cube.  It wouldn't be too difficult to drill holes into it for eye bolts.  Then you could hang it from the bridge.

Avanti posted:
gunrunnerjohn posted:

Maybe you need to find a big chunk of lead for a smaller form factor.

Depleted uranium, maybe? 

Maybe he can get someone to fire a shot from the M1A1 into the train room.  Once the damage is repaired, he has the heavy chunk of material to build the counterweight.

This looks to be about the right size...

 

Certified Pure Lead Brick (99.9% Pure) 26.2 pounds

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mike g. posted:

Thanks Carl,

I did try it on the back side and between the support legs, but when I raise the bridge the tail end would hit the actuator. The location where it is should be ok, as that part of the bridge support will be behind the wall on one side of the door entering the room. The Bridge is 40" long and my door opening is 32" so that means 8" will be out of the path entering the room.

Sweet! Now you have the power lift bridge setup.

First off I would like to thank everyone for there comments!

Second I would like to thank Mark, Carl, Max, RTR12, Pete, Stan, Dan, and John! Without you guys I would still be in the dark over this darn thing. Also now that it work you all have made my wife happy! Now I can do some of the things she wants done. She is a good woman and lets me do train stuff to a point and I know I spend to much doing it.

Thank You again to you great group of guys!!

Now to think of a new project that doesn't take a lot of money ( Scratch Build)

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