MF Technical help

1) It is, in fact, a hydraulic motor that normally runs the cable drum. Side note: the pump had to be replaced this season which resulted in MF's longest downtime of the season: 3:30pm one day until 10:15pm the next.

2) The emergency back-up system is powered by a diesel motor as shown in Jeff's second picture. The motor can be used to power the lift system as well as any other aspect of the ride.

Rideman, I was looking on your website at the knex cable lift hill, and I was wondering if you could explain it to me. I understand now how the system works, with the drive motor driving a drum with the cables. I understand how everything works, but being only 15, I do not know how to read electrical diagrams yet. I do not understand how the wiring is set up, and I don't understand how the switch works to reverse the polarity of the motor. Is there a way to reverse the polarity of any old electric motor? I have a hair dryer motor that I could easily attach a drum to, but it doesn't reverse. Is there a way to reverse this motor? Also, I drew out templates for the lift hill, and its going to be about 3 feet tall, just to give everyone an idea of its size. I also am looking to build the station on it, and the magnetic brake run behind it, and I want the brake run to be working. That I have a really good idea on how it works, and I am not worried about that. I am also going to construct a train for it, but I am clueless on how I'm going to do that as of right now. Thanks for all of the help!

If your allowed to, get some help from a parent, or anyone with a background in electricity or engineering.

My dad will be helping me, and he's the only person who I know that has any electrical experience, but he doesn't do it for a living, and he is not sure enough of himself to do anything without knowing how to do it.

Just a thought, if you have like a college near you, (community or university), you could try taking it in there and asking them for help.

Looking at the model lift idea on my web page...

I specify a DC motor, such as the motor supplied with the K'Nex model sets. This is because those motors are permanent magnet DC motors, and the direction of rotation is determined by the electrical polarity. That doesn't work with an AC motor. The K'Nex motor has a 3-position switch on the battery box which gives you a forward, reverse, and off position. That switch is a "SPDT" (Single Pole, Double Throw) switch. That means, it has a single set of poles, and two positions: the center pole, called the common, is alternately connected to one or the other of the remaining poles. The switch 2 in my diagram is a DPDT switch, which is functionally equivalent to a pair of SPDT switches with the toggles mechanically (but not electrically) hooked together.

The concept I show is that the lift catchwagon 1 gets pulled up the lift 7 by the motor 5. When the catchwagon gets to the top, it hits a mechanical arm 3 that toggles the DPDT switch 2. If you refer to the electrical diagram, you can see that the battery voltage flows from the battery, to opposite corner poles on the switch, through the switch to one side of the motor or the other, depending on which way the switch is thrown.

Hmmm...I just noticed that there is a line missing in that electrical diagram. There should be a connection from that unused DPDT switch terminal to the battery lead connected to the opposite corner of the switch.

Anyway, if it were just the DPDT switch and the motor, the catchwagon would go to the top of the lift, come back down, reverse the switch, and go back up again without stopping. So I added a limit switch at the bottom of the hill but above the point where the switch reversing mechanism gets hit by the catchwagon. That switch should be a "normally closed" switch: that is, there is a connection until the catchwagon brushes against it and triggers it. Then a normally-open pushbutton allows you to bypass the limit switch so that the catchwagon can finish its trip to the bottom of the lift, reverse the DPDT switch, and thus go back up again. :)

I hope that makes some kind of sense. The wiring diagram is truly simple, as the only things on it are switch contacts...and by looking at the information given with the switch contacts you can see that the pushbutton is normally open (the contact doesn't touch the connections) while the limit switch is normally closed (bar touching contacts).

If you build it, or something functionally similar, send me photos and I'll add them to the site!

--Dave Althoff, Jr.

Thanks a lot rideman, and anyone else who contributed to this thread. I have one more simple question though, what would you recommend me using since I'm NOT using a K'nex set. I dont have the motor that came with it. Is there any thing anyone would recommend? *** Edited 12/19/2004 4:09:41 AM UTC by SFSL_Guy07***

I know this may sound stupid, but why don't you just buy a "replacement" motor from K*Nex?

The K'nex motor set is nice because it is a small DC motor attached to a gearbox, and it is a decent size motor, so it can actually do some work. It uses a worm gear on the motor to drive the gearbox, so the output shafts (there are several, depending on what speed you want) have no appreciable slippage.

That said, almost any motorized construction toy design may include a suitable motor assembly (K'Nex, Erector, LEGO, etc.)

Of course, you could also eliminate the motor entirely and put a crank on the thing... :)

--Dave Althoff, Jr.

Thanks Rideman. I finally understand how it all works, but the only thing that still baffles me is the limit switch at the bottom of the lift. I am probably missing something. I know its purpose, but I guess since I dont understand how it works, I'm confused still. Thanks!

One other quick question, are all DC motors permanant magnet ones that can be reversed?

Wow, I'm really learning a lot:) *** Edited 12/19/2004 4:48:12 PM UTC by SFSL_Guy07***

The idea behind the limit switch is that when the lift carrier approaches the bottom of the lift, it will trigger the limit switch, causing its contacts to OPEN, thus shutting off the motor. So that would be something like a "cat's whisker" switch, or something like this (picked at random from a Google image search). It triggers before the carrier gets to the reversing switch at the bottom of the lift. So when the pushbutton is activated (bypassing the limit switch), the carrier continues running backward down the lift, hits the reversing point, and reverses. The pushbutton has to be held until the carrier clears the limit switch on its way back up again.

As for motors...all generalizations are false, including this one. Most modeling motors are going to be reversible.

--Dave Althoff, Jr.