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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 ?

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