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

Attachments

Images (6)
Last edited by mike g.
Original Post

Nice creation, Mike!

Will it travel to vertical? It looks like you gave up about 10" of aisle.

 

Attachments

Images (1)

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

Carl, I just measured and I lose 9" of aisle. It can go vertical but I have to leave a little so gravity can help to down word motion, I am looking at possibility of building a gear drive system buy cutting my own gears.

That a pretty neat idea, power lift! Looks really nice and good idea with the drill too.

RTR Thanks, I am rethinking the drill motor, my brother gave me his kids old battery operated corvett, I took it apart and might use the motor and gear setup  in it.

Max its a Pratt Bridge from Atlas.

If you happen to have an old electric screwdriver lying around, it may be a good choice as a drivetrain in an application like this.

Hi Pete, I was thinking about a electric screwdriver, but there is no easy way to control the speed of the motor, buy using a dc I can control how much power just by a dial.

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.

Attachments

Images (1)
Videos (1)
20161031_160544
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?

Hi Frank, I'm not sure if they would work either. I hope Stan says something about the speed controller that Carl found.

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 ?

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?

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.

Another method I have used on small animated projects is the screw shaft drive.  Similar to some garage door openers.  On this LGB mart craneI used the screw drive to raise and lower the boom and another to extend the boom.  

 

https://youtu.be/jFNIfV8RZ7w

Hi Dan, I like that idea, but I would have to find an old screw type opener and kit  bash it. But that's ok, isn't that what its all about. I will start looking around for a free one. Till then I'm still open to ideas!

I think to even out the up and down speeds, the counterweight would be a good start.  That's how the real bridges do it.

Thanks John, that's something I am going to work on today, after Christmas light install, Have to keep Momma happy first!

A screw drive is a very good idea. No need to kitbash. There are very good high-power units available on eBay or Amazon for reasonable prices. 

Go to eBay and search for "linear actuator". 

Here's a random example:

linear actuator

These are very nice devices. I should have though of them first.

Attachments

Images (1)
Last edited by Avanti

The counterweight is still a very good idea, even with this device.  Equalizing the load going up and down will make things work much smoother.

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.

 

Attachments

Images (1)
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.

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

 

Attachments

Images (1)

Add Reply

Post
OGR Publishing, Inc., 1310 Eastside Centre Ct, Suite 6, Mountain Home, AR 72653
330-757-3020

www.ogaugerr.com
×
×
×
×
Link copied to your clipboard.
×
×