10 replies to this topic

[OddlyCreative]

Hello all,

I am planning on building a to-scale replica of King da Ka out of classic SSC K'nex pieces. The coaster will be around 17-21 feet tall and the launch section 25-30 feet long (I am still working out the scale factor). I want to have an automated launch, and I am looking for suggestions on what to do. The coaster will be outside.

I have no almost no experience with Arduino, but I suspect I will need to use one. Also, I will likely need to use non-K'nex power such as a drill or servo motor.

 

In order to help save pieces, I have developed a 3D printed adapter to connect K'nex pieces to tripod screws, which allows for affordable supports (6-foot used tripods are only a dollar at my local flea market).

 

 

Questions for you all:

 

Will rubber bands / surgical tubing be strong enough to launch the coaster? Also, will K'nex pieces be able to handle the force over such long lengths (30 ft)?

If I employ a flywheel-style launch, how will I be able to reset + properly maintain tension on the catch car?

What is the best way to create the path for the catch car to travel on? I have seen it done a couple different ways.

Please mention any other relevant information or tips.


Many thanks,
OddlyCreative

 

 

[CrayCray for coasters]

Now this is where i can help, still prototyping the high power launch for now but i shall post in this topic with updates when there are any

[Alabastine]

You could take a look at my Ascension, it has a cable launch with an RC motor and the working principle is actually the same as on the real Kingda Ka. I run it with RC car parts and a remote. Now an RC car ESC should also be controllable by Arduino but I have no experience with that (yet).
The cable loops around back onto the drum. Also you'll need a tension pully on this (look at the orange parts moving in the launch). I built a slipper clutch so that the motor doesn't pull everything apart when the cable reaches it's stop.

 

I also had trouble creating a guide for the catch car and in the end I botched something to line it up only at the start, so I would look elsewhere for a solution on that.

 

Personally I really don't like rubberbands, they deliver decreasing force over distance because it's just a spring. That means you need a lot of force through your K'nex to pretension the spring, but because it falls off quickly you might still have trouble reaching the required speed. It's also not a realistic principle in real scale which is important for me personally.

 

Here's the video:

https://www.youtube....nnel=Alabastine

[OddlyCreative]

Alabastine, Your coaster definitely is what I am going for! I know that there is going to be a lot of things maintaining tension on the back of the launch, so I'll need to experiment and study up on how to do it. 

I think I have a solution for creating a path for the catch car, I'll post soon in a construction post. I am going to try and 3d print a custom catch car so that there is no need for a catch car track at all! 

I also want to experiment with using weight to constantly maintain tension on the back of the catch car; when the launch is done, the motor will just need to unwind and the catch car will be pulled backwards.

Thanks for your responses,
Oddly

 

[Alabastine]

Good to hear! Feel free study the footage of my coaster. With regards to maintaining tension, you basically only need a pully that can move and has a preload to it, somewhere behind the catch car (my tension pulley is loaded with rubber bands). 
Because in my launch (and in Kingda Ka) the tail end of the cable loops back around to the cable drum and unwinds during launch. This video explains how it works IRL very well: https://www.youtube....rtofEngineering

 

Keeping tension on the back of the catch like you are describing also works, that's basically what I did on Griffin with twisting rubber bands (wouldn't do it exactly like this though, it was not 100% consistent): https://www.youtube....h?v=D8SY8Tps7c0

 

3D printing a catch car is definitely a good idea yes .
 

Edited by Alabastine, 08 January 2022 - 05:14 AM.

[RCT2123]

Thanks for the idea Alabastine!  One of these days I'm going to work out a launch for my coaster, and it'll look something like yours.  I really like the clutch.  Feel free to reach out to me for help with Arduino stuff (email is best, tommysantoyo@gmail.com).  I'm not an expert by any means, but software is my day job, and I have an engineering degree, so electronics aren't too tricky.

[RightWayTrey]

Surgical tubing is amazing and should work great.  I dabbled with automating a launch like this and got it to work with K'nex for about 6 foot launch height.  May be hard to get to 17 feet but I think you could creative on how to support the pulleys. 

 

Here's the video of my launch

https://www.youtube....h?v=PTHByxXctYs

 

(wow this is an old video I have been away for a long time)

[OddlyCreative]

RightWayTrey, what is the use of that sideways cart? I can't seem to figure it out!

[CrayCray for coasters]

RightWayTrey, what is the use of that sideways cart? I can't seem to figure it out!

I believe it ties in with the counterweitght in the center of the tophat, quite an intuitive design

[RightWayTrey]

RightWayTrey, what is the use of that sideways cart? I can't seem to figure it out!

 

Took me awhile to figure it out, I had forgotten what I did!

 

All the sideways car is doing is taking up the slack of the string for the motor reset system.  There are 2 drums rotating under the track in the beginning of the video, a ratcheting drum for launch and a drum attached to a motor.  The ratcheting drum (farther forward along the launch track) winds up a string which tensions the surgical tubing.  It also has a second string which attaches to the motor drum.  The motor drum pulls tensions the ratcheting drum for launch, then I reverse the motor to let out enough slack for the launch.  The sideways car just ensures that this slack doesn't get caught on anything during the launch.

 

[Terracoon9]

You can do it with normal elastics, it is indeed good to use a non knex motor, I used my rc car motor, it takes about 10 seconda to wind up the elastic and it shoots about 1,5 high, I used lego mindstorms instead of arduino, its little bit easier, this is mine: