Metal won’t launch through model mass driver

[bz1234]

Hello,
I’m working on a model mass driver project and it’s due in 2 days. Here’s the link to the project that I followed: https://www.sciencebuddies.org/science- ... ass-driver . I’m having a problem with the metal launching through the tube. I’ve tried to see if the metal will launch through the tube if the coils were connected to the battery directly but it still wouldn’t work. None of the metals weren’t able past/ launch through to the first coil. The arduino and the 4 channel driver seems to be connected when the program is run, so I have no idea what part of my project is not letting the metal launching through.
Please help asap. Thank you!

[bfinio]

Hi,

To clarify the physics here - if you connect the coils directly to the batteries, they will always pull the metal "in" toward the center, so the metal will never make it past the first coil. This happens because the piece of metal is ferromagnetic but is not a permanent magnet - it is temporarily magnetized by the presence of the external magnetic field from the coils, and will be pulled in toward the center of the coil regardless of which side it starts on.

The mass driver works because the hall effect sensor detects the changing magnetic field as the piece of metal passes through and shuts off the coil, allowing the metal to travel on to the next coil instead of being pulled back to the first coil, and so on.

So, if it's "not working", how do you figure out how? We can't tell you exactly what's going on just from the picture, but I can give you general advice for debugging a complicated system like this: you want to isolate and test individual components as much as possible to identify the source of the problem. In this case, that might look something like this:

1) Simplify the system by reducing it to a single-stage mass driver to start. Disconnect your 2nd and 3rd coils and Hall effect sensors. Once you know you have one stage working, it will be easier to get the other stages working.
2) Make sure your first-stage coil is working by connecting it directly to the battery. The piece of metal should be attracted to it in the tube.
3) Make sure your driver board is working by writing simple code to just turn it on and off (similar to how you would write code to blink an LED on and off using digitalWrite), without using any readings from the Hall effect sensor. You can tell that the coil is working and toggling on and off by holding a compass near it and seeing the compass direction change, or holding the tube vertically and putting the piece of metal in (if you time it right, it should be initially attracted and held in place, then it should fall when the coil shuts off).
4) Make sure your Hall effect sensor is working - write code to take the sensor reading and use an IF statement and serial print commands to print, for example "magnet detected" or "no magnet detected" depending on the sensor reading. Test the sensor by holding a *permanent* magnet near it - that way, you can test the sensor's functionality independent of whether your coil and driver board are working.

You need to go through that entire process just for the first stage to ensure that it is working. Once that is working, you can add a second stage, and so on.

It's also a good idea to make sure there isn't a simpler physical explanation for any problems, like the metal getting stuck because the tube diameter is too small.

Hope that helps!

[bz1234]

Hi,
Thank you for clarifying how it works. I’ve tried directly connecting the batteries to the first coil, letting the metal go through just the first coil, but it doesn’t get sucked into the tube. It just stays there and doesn’t move at all. Also, I’ve tried different batteries and it still doesn’t work. The size of the metal and acrylic tube are perfectly fine. Is there any other way to make it launch besides the ones you listed down below?
Thank you again!

[bfinio]

Ok - first warning, the alligator clips and exposed ends of your copper wire are very close together and nearly touching in that picture - if they touch that will short-circuit the battery and drain it very quickly (and possibly cause things to get dangerously hot), so watch out for that.

Next - it's hard to tell in your photo, but did you sand off the insulation on the wire where the alligator clips are connected? The insulation has a more reddish color and when you sand it off it should expose the underlying copper, but it can be hard to see and tell the difference depending on how exactly you're holding the wire and how light is reflected. If you didn't sand off enough insulation, then you won't have a closed circuit and no current will flow, so the coil won't do anything.

Next, do you have access to a multimeter and/or a compass? Those tools will let you confirm that current is flowing through the coil or that it's generating a magnetic field, respectively, but my best guess right now is that you didn't sand off enough insulation so no current is flowing at all.