EMF Pinewood Derby: A Practical Physics Project

[Stinson]

Also, the car battery isn't blowing the 10A fuse (very little time connected) but the smaller lantern battery seems to result in more motion. That is unexpected.

 

[sophiecentaur]

Also, the car battery isn't blowing the 10A fuse

It's encouraging that you are getting some motion.
If you have a DMM, you could measure the resistances in the circuit. That would give you an idea of the actual current flowing. It looks as if your coil circuit has a resistance of more than 1Ω, if 12V doesn't blow the fuze. That's fine. The fuse is there to protect against the effect of shorts and my 10A guess must be about right. However, why the car battery is not performing better is a surprise. Poor connections or a high resistance fuse holder, perhaps?
How are you supporting the moving magnet, to deal with the problem of attraction towards the stator? Have you understood the point I am making about that and how it's dealt with in a normal motor?

 

[Stinson]

Yes I am understanding, and I thank you so much for your patient and persistent support. It turns out my error in theory on paper was a missunderstanding of how the permanent magnet would react to the flux of the electromagnet. Now that I can physically see the permanent magnet does not travel from the "N" to "S" end of the electromagnet, but instead achieves equilibrium dead center, reversing polarity at that point to to push/pull half way though a single electromagnet is clear. I just wasn't getting that on paper looking at endless flux diagrams.

So the car starts at one pole, is pushed to the middle, polarity reverses, car continues on to the next magnet, repeat repeat.

I have 4 working electromagnets and enough magnet wire for 10 more, so I can keep this up for a good long while. I haven't used any brand new magnet wire yet, only what I have salvaged used. It made sense to use the old stuff to work the kinks out of wrapping the windings before I use the brand new spool. There were some noticeable blemishes on the used wire with close inspection, but it checked out on the ohm meter.

I currently have the magnets secured to the nose of car with painter's tape. Once I feel satisfied I am out of the orientation experimentation phase, I will cut a hole in the nose of the car and bondo the magnet into the frame.

The fuse is attached with some small alligator clips I picked up at that auto parts store when I got the fuses. Jumper cables to battery, small alligator clip from positive jumper cable to fuse, alligator clip from other end of fuse to electromagnets (solder), and then I'm just touching the ground to the negative alligator clip for now. Haven't messed with shoes and permanent placement yet, though I did pick up a piece of aluminum sheet metal to make the shoes and track with.

I figure I'll have 2 wooden rods like chop sticks or popsicle sticks coming out the sides of the car in line with the magnet. I'll fold a piece of paper to function as a spring and hot glue it facing down from the stick. Then hot glue some sheet metal to the paper. One side will be initial coil initiation and the other side will be polarity change. To figure out where to put the sheet metal switches for the show, I'll simply run the car. When it is close enough to the magnet to pull in, start the track. When it stops, stop the track and start the polarity change. I'll bondo the gaps smooth so the shoe doesn't physically realize it isn't on the sheet metal.

 

[Stinson]

Just got back from church and got to try out the double wrapped coil I finished just before I had to take a shower and leave 5 minutes late. That makes a BIG difference, wow. I expected it to, but it exceeded those expectations. I plan to step it up as I go down. The first 3 coils have 90 wraps, the next two will have 180, then 270, then 360

Just for the lolz. I expect the bigger difference I'm seeing from 180 is because whatever friction retardation or anything else holding the first 90 wraps back are already taken care of. It's more than double the distance.

I started with the single row coils because the worst shape material I had required that recepie. As I go up in rows I'll also be using brand new wire for the first time. The double coil I just made was actually in the worst shape of all.

 

[sophiecentaur]

This seems to be going well. You should try to 'tune' it by subtle changes in the phases and the spacings of the shoes. It could be impressive (but no promises!)

 

[Stinson]

The problem with tuning my shoe design with subtle changes is akin to dressing for cold weather. I'm in Florida so everything below 70 is cold weather. It's easy to take off more than you need. I just use some tin snips to trim the sheet metal accordingly. Realizing I trimmed to much and wanting to backtrack on the other hand...I only have a small 8"x18" sheet to span the entire project. This sure is fun though.
I just tried my first 3x layer coil (90+90+90=270 wraps of magnet wire around the core). I'm noticing drop off in efficiency compared to the MASSIVE boost from 2 layers, but it's still a solid gain. The 3x is so strong however that unless I'm pushing away from a distance, the coil jumps out of the groove and kisses the magnet. I've already planned for that with a bag of zip ties, but I'll need to actually zip tie the 3x coil into to track before I can even play with it.

 

[sophiecentaur]

Can you adjust the spacing and the phase, though? You may not need to cut pieces off the shoes if you put in short lengths of insulation (?)
It's good that it seems very lively. Could you try with lower volts? A chunky 0.1Ω resistor would do or even just a length of the wire you already have,in series with the whole thing.
Any chance of a photo of the working arrangement?

 

[Stinson]

This was ~ midnight last night when my first working coil actually moved the car. I promise I'll give you a video walk around of the final product when it's complete. I'm actually in a team of 4. So far I've done 100% of the work but I decided to hold off on mapping out the individual coil strengths for the shoe and bring the whole contraption with my new found knowledge of how to make it work into class tomorrow. I'll let the rest of the team help me plot the strength of my 5 current coils (90 wraps x3, 180 x1, 270 x1). And probably have them each make a coil of their own. They aren't slackers, they just aren't good at dumpster diving for parts. I'm sure I'll add more coils as well but for now I want to explain to the rest of the guys the who/what/where/when/how of the thing.

We are in a strange physics pilot program which the syllabus claims as "no lecture no test" physics. We meet Monday, Wednesday, Friday for 2 hours and the entire class is a lab. It started at Harvard and my university is one of several others trying it out. They drop large practical projects and/or papers like these in our laps with a sink or swim attitude. The idea is that instead of spacing out in a lecture you'll be forced to teach yourself and make creative working examples of the lessons or you simply don't pass. Seems to be working pretty well. I sure know a hell of a lot more about electromagnetism tonight than I did two weeks ago. There are 16 groups and each is doing a project on electromagnetism. I know someone is making a rail gun, which was my first though but the rest of my group had reservations of bringing a "gun" to school. Hah. Another group who's proposal I overheard is making a hand crank generator. I don't know what the other 13 groups are doing. One my group's members said, "lets move a car down a track", and here we are. The next (and last) project will focus on optics.

We are allowed to use any resource imaginable with the single exception of Chegg, so coming to forums like this for advice isn't frowned upon. In the end you either make it work or you don't. Projects are graded on a scale of 0-3.
0 = you didn't even try
1 = you tried but it wasn't very impressive for whatever reason
2= exactly what they were looking for, good job
3 = exceptional (it wouldn't be uncommon for there not to be any 3's though I made one for a paper describing the electrostatic mechanisms of the nervous system)
All 2's is an A for the course, but a 3 can offset a 1. If you get a single 0 the highest grade possible is a C regardless of how many 3's you may have and two 0's is automatic failure.

This was tonight, beginning to map out the shoe. I complete the first coil as an example to my teammates but I'm going to walk them though doing the others themselves. I'll actually apply the sheet metal either tomorrow night or Tuesday, but I want them to at least play with the battery and draw the lines if nothing else. I'm using the car battery exclusively now by the way. Went to WalMart tonight and picket up some more cheap alligator clips, the ward off any extra resistance from touching the speaker wire to jumper cables. I was getting tired of arc welding the wires over and over anyway.

I never intended the permenant magnet's final resting place to be taped to the grill of the car. I'll move them back, probably toward center of mass. The measurments are still valid though, as the magnets frame of reference won't change. Just move the lines proportionally to match. Love your idea about insulating the shoe. I'll probably just use one long strip of alluminium with electrical tape representing where to cut, just dial each coil in one at a time until it's right. Then cut and wire each piece of the shoe's track afterward.

Notice in the above image the coil is zip tied under the track. This was what happened before that development:

My first 3 coils, I've sense gotten much better. I'll have to get a picture of the new ones. Anyway, thanks again for all your help. I'll make sure to update my progress when I have progress worth updating. I'm feeling pretty confident at this point. It's going to happen, and it's going to be awesome.

 

[sophiecentaur]

I'm actually in a team of 4.

You are the little red hen!
If you can reproduce that successfully on a longer scale, it should get you a 2, at the very least. Getting the switching contacts right will be your next thing. There are several alternatives to a simple sliding shoe arrangement (although that should do the trick ok). Depending on whether your other 'helpers' could do it, an optical position detector would be cool and it would be easily adjustable, to get the timing and length of pulse just right.
Once you get this DC system working you will begin to see the advantage of a proper linear motor with and AC feed. But, one thing at a time. . . .

 

[Stinson]

It was a bomb with the group. I'm just going to press on without them and if we all share a better grade because of it...that's just how group projects work sometimes.
One member stayed with me for 2 hours connecting circuits and seeing how everything works. He was really interested and thought it was great. I think he understands the basic premise.
The 2nd member wants a single coil to push the car a couple inches onto a downward sloping ramp without all this "alternating circuitry mumbo jumbo". He walked out before I hooked anything to a battery. He thinks we should do it his way because he came up with the original idea of moving a car.
The 3rd, who is the 2nd's fiancee, didn't bother coming to the demonstration.

I can tell the advantages of AC from various literature I have read. I'm excited to learn more about it in the future and will probably have opportunities in other classes to modify this basic design in different configurations. Like you say though, one step at a time.

 

[Stinson]

I think I'm going to dismantle two of the 3 90-wrap coils, saving one for pass around demonstration, and convert them to 180-wraps. I just don't feel like hack sawing and filing more cores at the moment. I'll be using brand new magnet wire now, as I think the prototype coils from salvaged wire I've made thus far have served there intended purpose of teaching me how to do it properly. I hope to break major ground today.

 

[Stinson]

Well I finally blew a fuse. bahahahaha
Still have 9 more so no big.

 

[sophiecentaur]

Stick with it. Your passengers will appreciate you in the end and you will be richer for the experience.

 

[Stinson]

Wound the brand new coils before dinner and just hooked them up to real juice aside from just an ohm meter. I'm getting 14" of push in a single direction from a single electromagnet and the track is only 3' long. The original plan was to push the car up an incline, but I only have a tabletop for the display. One of the group members suggest I use a break magnet to serve as an invisible fence and I think thought that was a good plan. So this thing is going to be moving pretty damn fast, and at the last second it will come to a halt.

 

[Stinson]

Coming right along...Ignore some of the wording, I'm just copying and pasting from my Facebook post from a couple seconds ago.

Bottom circuit route, power and ground coming from each coil lead so they can work in both directions to pull the car in and then push it away when it passes.

The leads were too short to reach a crimp under the plywood so I got to show off my soldering skills. Soldering 3 wires together, one of which (the magnet wire) doesn't take well to soldering, is a nightmare. I started getting mad at my lack of 3 hands. Even that would be tough, it's a 4 hand job. So I just crimped.

Dismantled the 2nd and 3rd coils I made in the prototype phase. I kept the 1st for sentimental reasons. Used the cores from those 1 layer coils (which also had used wire) to make these 3 layer coils. Got lazy and didn't feel like spending half an hour hack sawing more cores. The brand new wire is much thicker than the old wire I was using. This mean less wraps per layer. The older wire feels like wrapping a spiderweb by comparison.
These are pushing my car 13 inches 1-way. When everything is hooked up they will be working both ways. The track is only 3 feet long, so the car should be moving pretty quick once you add them all together automatically.

That automatic part is what I'm working out now. I want to flip a switch and have everything just...work.

 

[Stinson]

I made a typo but can't edit. One post says 14 inches of movement and the other says 13. It was 13. I just have fat fingers and hit the wrong key. Still...13" is a pretty healthy push considering I'll have 4 separate pushes and 3 pulls in a ~24" space. I might squeeze even more force out of the coils once I prefect the timing via a shoe. I'm still just mashing alligator clips together to complete circuits at the moment.

Just re-read this entire thread start to finish and had a good hearty laugh at my ignorance just a week ago. Listening to your initial advice and understanding exactly what you were saying as if I was the one typing it to my past self was quite an experience. Then I got to listen to that past self from just a few short days ago come up with some well meaning but confused retort. It's a real testament to how much I have actually learned throughout this process.

Didn't get the shoe finished due to a small unrelated crisis, but I know exactly how I want to do it and I'll go for it tomorrow after class.
The presentation is Friday but I have a differential equations test Thursday and need to wrap this up to exam cram variation of parameters and mathematical models of spring loads. Once I jump that hurdle I can start the real electrical classes and start to think of myself as an electrical engineering major on more than just paper. You have helped me so much and I hope the finished product is something we can both be proud of. I was so lost when I made my first post here on Physics Forums that even I'm not exactly sure what I was thinking anymore.

 

[sophiecentaur]

Soldering the enamelled wire could be easier if you clean off the enamel with some emery paper - even if it claims not to need it - then twist it together first. Only two hands needed, that way!
Stick at it. From what I have seen, you have a pretty good chance of getting a result here.

 

[jim hardy]

yes, cleanness is the key to soldering. Sandpaper it down to shiny copper. A ;little bit of soldering flux will work wonders. Heat the wire not the solder.

 

[Stinson]

I think my issue with soldering is the iron itself. A $5 Walmart special, cheapest of the cheap. It boils flux but I have to rub the solder in a downward motion along the tip to get it to melt, then it freezes solid again as soon as I stop moving due to the heat absorption. It will literally solder the coil of solder to the hot soldering iron and I have to chip it off with a screw driver. It's JUST hot enough to melt the solder if I don't keep it in one spot.

I'm still a super amateur at soldering but plan to eventually invest in a decant setup, anticipating I'll be doing a lot of it in the semi-near future. Or is what I got considered perfectly normal and I just need to focus on my execution? Any suggestions on what to buy keeping in mind I'm poor? Literally every dollar I spend is funded through student loans.

 

[Windadct]

Looks like you are pretty well into constuction, but try to minimize the "gap" pr the distance between the Coil and the Magnet. Thin plywood, mount the magnet as close to the "track" as possible.

I see you have a CFU tag, Are you at Central Florida?

 

[Stinson]

UCF, Sure am! The hood design is the school emblem. I think I came here the night I painted it, so that was the main reason for the tag I suppose.

 

[HawaiiAl]

Have you thought of using 180 degree shifting coils.Shutting off as your "car" is just above them,then rotating 180 degrees then powering up again after the car passes them.This way you'll get the most from each coil on the track.
The cars magnet used as the switch.This way you'll get a push & pull effect on the car automatically.I would definitely use DC current!AC needs to be switched to DC anyway.
I'm not a physicist so this is just a understanding.I know that coils being switched isn't as reliable as switching there direction.The iron tends to hold a magnetic direction.Good luck!I know you can do this!

 

[Stinson]

Yes I'm well into that spectrum. Taking a break from cutting sheet metal to use as a printed circuit for the shifting at the moment actually.
This is a science fair type setting, so I want random people to intuitively see when the coils are off or on and which direction they are going at any given second.

 

[Stinson]

Presentation pushed back to Monday because some of the groups aren't close to ready. I'm basically done. My original spring system for the shoe failed. It consisted of a trimmed 3x5 index card folded into a spring with a metal plate on the bottom. It seemed ideal because the index card would be study enough not to bend during forward motion, allowing me to more percicly pinpoint the contacts in relation to the permanent magnet. However, the added friction was eating up 2/3 of my forward motion. I thought about it for a few seconds and figured if that was too heavy...a gum wrapper would work. Before I found the gum I decided if a gum wrapper will work, why not alluminium foil? So I have foil hot glued to a popcicle stick and it works wonderfully. I have 2 strips running the entire length of the track and a 3rd strip I'm going to cut up into pieces for both sides. Still working out where I should cut but the system works as well as I would have hoped. I'm getting massive motion from both push and pull. I could easily travel the length of the 3' track utilizing only one or the other. Won't see both together until I'm ready to cut up pieces of track and wire everything together at once, but any acceleration boost is just icing on the cake when you don't technically even need it. I can't wait to see it happen. Right now I still just have 2 full length tracks for the same shoe and electrical tap blocking current to dial it in before I start sawing...but it clearly works. Taking the project with me to school again tomorrow, hoping to get the rest of the group on board.

My biggest issue right now has nothing to do with electricity or magnets. I need to properly align the axles of the car. It likes to drift to one side and other random issues of that nature. I compromised some of the factory pinewood derby front axel grove sticking a magnet under the nose of the car facing down in the experimenting phase. I knew I was doing the damage when I did it and planned all along to repair it later. With the electromagnetism part of the project all but wrapped with a bow, doing that sort of routine maintenance is my next real goal. I'm going to go all out and wet sand the nail axles for optimal friction reduction, repaint the car (the same way but touch-up for all the chips and burs from playing hard), etc. etc.

I couldn't be happier with my results or position of timing still 5 days from presentation day. The only thing that would make it cooler is if I did a Sonic the Hedgehog style loop-de-loop where the car has so much centrifugal force from the forward motion of the magnets that it can travel upside down. I think I will do that in my own time just for the sake of doing it, but for the graded presentation I'm just going to keep it flat.

Think I got this one in the bag fellas!

 

[the_emi_guy]

Presentation pushed back to Monday because some of the groups aren't close to ready. I'm basically done. My original spring system for the shoe failed. It consisted of a trimmed 3x5 index card folded into a spring with a metal plate on the bottom. It seemed ideal because the index card would be study enough not to bend during forward motion, allowing me to more percicly pinpoint the contacts in relation to the permanent magnet. However, the added friction was eating up 2/3 of my forward motion. I thought about it for a few seconds and figured if that was too heavy...a gum wrapper would work. Before I found the gum I decided if a gum wrapper will work, why not alluminium foil? So I have foil hot glued to a popcicle stick and it works wonderfully. I have 2 strips running the entire length of the track and a 3rd strip I'm going to cut up into pieces for both sides. Still working out where I should cut but the system works as well as I would have hoped. I'm getting massive motion from both push and pull. I could easily travel the length of the 3' track utilizing only one or the other. Won't see both together until I'm ready to cut up pieces of track and wire everything together at once, but any acceleration boost is just icing on the cake when you don't technically even need it. I can't wait to see it happen. Right now I still just have 2 full length tracks for the same shoe and electrical tap blocking current to dial it in before I start sawing...but it clearly works. Taking the project with me to school again tomorrow, hoping to get the rest of the group on board.

My biggest issue right now has nothing to do with electricity or magnets. I need to properly align the axles of the car. It likes to drift to one side and other random issues of that nature. I compromised some of the factory pinewood derby front axel grove sticking a magnet under the nose of the car facing down in the experimenting phase. I knew I was doing the damage when I did it and planned all along to repair it later. With the electromagnetism part of the project all but wrapped with a bow, doing that sort of routine maintenance is my next real goal. I'm going to go all out and wet sand the nail axles for optimal friction reduction, repaint the car (the same way but touch-up for all the chips and burs from playing hard), etc. etc.

I couldn't be happier with my results or position of timing still 5 days from presentation day. The only thing that would make it cooler is if I did a Sonic the Hedgehog style loop-de-loop where the car has so much centrifugal force from the forward motion of the magnets that it can travel upside down. I think I will do that in my own time just for the sake of doing it, but for the graded presentation I'm just going to keep it flat.

Think I got this one in the bag fellas!

You may be able to reduce friction and increase electrical conductivity of the "shoe" if you can cut the aluminium foil into thin strips for making contact with the track. This is akin to how brushes work in a motor, more guaranteed contact area with less normal force.

 

[Stinson]

My main worry at the moment in that regard is too little friction. There isn't anything but a twist holding it to the shoe. I was thinking about hot gluing a small nut to the foil high enough so the nut doesn't drag on the track but low enough so it forces the foil down from its base. They are already pretty thin. I hot glued both ends of a strip in a circle onto the top of the popscicle stick, pinched what was left together, and bent it to contact.

They are only ~1/2 inch wide and the distance between the shoe strips is wider to prevent one of them from touching both sides and shorting the battery. The trouble with testing is that if the car wonders off course more than the thickness of the strip - I lose current. Just can't have my cake and eat it too.

 

[Stinson]

Tried to make the system fail on purpose without shorting just to test the limits and one of the magnets started smoking (expected). I'm curious about long term damage to the magnet from this though. Do you think it will be good as new when it cools off again or will it be a little retarded? I need to do this more scientifically with the multi-meter. I don't have any instruments able to detect magnetic field other than other magnets though. So if it's slightly weaker I might not know it.

 

[Windadct]

Sounds like a good job, and you learned a lot.

My Brother is an Associate Prof at UCF, that is why I asked

 

[Stinson]

Oh that's awesome. I really like the school. Nice campus, all of my professors (I just started and cherry picked from rate my professor so take that with a grain of salt) have been great. There is an engineering lab I discovered yesterday where you go to take problems like the one I'm working on. They have a nicely stocked complementary tool room where you just go and hash stuff out. Sat across from a girl who was building a small remote controlled boat for a race next week.

 

[Windadct]

They have adopted a good, Hands on practical approach. I was very dissapointed by our state uni using the exact same curriculum that I had 30 years ago. You still need the academics, but practical learning is the best thing to have changed in education since then.