Joule Mobile Mass Transporter.

[Ivan]

Hi bradleyshanrock-solberg,

Thank you very much for the advice. Based on what you said, I have to start from scratch. Now I am coming up with the design of my cart. Here it is:

Wheels- CDs
Body-Undecided. Here are my options though: Wood (I dont know how big though), or Video Casette. I don't know which to choose. Any Suggestions?

Questions: 1. How do I make the axles? I need to know how to connect the CDs on each end and how to connect to the cart.
2. How do I wrap around the axles? A bit confused. Alittle clarification.

Clarification: 1. Can you clarify the pulley thing?

Thanks in advance.

[bradleyshanrock-solberg]

Any kind of string that will hold the weight reliably and that is handy enough to tie off should work ok. You don't want thick twine and if you use something like fishing line it might not hold the weight or might be too stiff to work with.

The main properties of string to worry about are strength, flexibility and "stretch"...if they have a lot of spring in them the weight will bounce up and down after it is dropped.

But almost anything should work. Ordinary kite string, for example.

[Ivan]

Hi bradleyshanrock-solberg,

Thank you very much for the advice. Based on what you said, I have to start from scratch. Now I am coming up with the design of my cart. Here it is:

Wheels- CDs
Body-Undecided. Here are my options though: Wood (I dont know how big though), or Video Casette. I don't know which to choose. Any Suggestions?

Questions: 1. How do I make the axles? I need to know how to connect the CDs on each end and how to connect to the cart.
2. How do I wrap around the axles? A bit confused. Alittle clarification.

Clarification: 1. Can you clarify the pulley thing?

Thanks in advance.

I am sorry. I dont like doing this. But can you answer my question please? Thank you very much and sorry for this repetitive post.

[bradleyshanrock-solberg]

Arg. I just posted a big long reply and it timed me out. Let me try to summarize.

0. I like the VCR cassette idea for a body. It's pre-built and very sturdy and easy to drill into.

1. CD wheels. Too narrow and slippery if you use just one to grip the ground well or to attach to anything. If you glue 2 or more together and do something like wrap a rubberband or electric tape around the rim, it might grip well enough.

2. Wheels to axle. Same problem. More CD's make it easier to grip, but CD's have this big hole in the middle. I read somewhere about somebody using wine-bottle corks to grip the inside of CD's...it's about the same size and cork can be compressed to fit and it then expands and grips...the same thing that makes it good for wine bottles would make it good as a tool for gripping the axle. After stuffing a cork into the CD assembly, you could drill out the middle a bit smaller than the axle and the axle would probably be gripped well enough.

3. Axle....consider those large, round pencils that grade school children use, or that are sometimes seen as souveniers. They're about the right shape and size and very sturdy. Larger diameter is good for gripping the cork well but won't be too big for a VCR cassette.

4. Pully assembly. Take a soda or water bottle, plastic, probably 1 liter or less. Cut the top and bottom off (knife or even scissors) so what you have is a cylinder. punch a ballpoint pen or similar round, smooth object through the top, with enough height so that the weight
can fall the right distance if the top of the weight is raised to the ballpoint pen position.

5. Attach the cylinder to the VCR cassette, with the pen positioned directly over the axle. You can probably just duct-tape the thing on, but if it isn't sturdy enough that way, you can take a larger bottle, make vertical cuts in the cylinder to the height you want it to really be, and fold the bottom out as flaps that can be used to screw the assembly to the VCR cassette or provide more surface area for the tape.

6. put the weight inside the cylinder and thread your string over the pen and down to the axle (you may need to drill a hole in the cassette for this purpose. There needs to be enough string so that when the weight is at rest, the vehicle can roll freely. This might be done by tying it onto the axle loosely, attaching it firmly (drill hole in axle, thread the string through the hole) but with plenty of extra string or not attaching it with anything studier than a bit of tape. You will have to experiment.

7. prime it for racing by rolling it backwards until the weight is at the proper height. Let go. Ideally the axle should turn, the wheels turn and it goes forward.

Troubleshooting #7

If it goes forward but stops too soon, try lubricating the axle. Graphite from a pencil or grease can help.

If the wheels spin without the car going forward, you don't have enough friction. The easy fix is more weight over the axle, but you may need to glue on more CD's to the power wheel to thicken the wheel and get enough surface area to get some traction.

If the CD wheels spin around the cork, you need either more CD'sor a bigger cork or both. (more CD's give more surface area to grip, a larger cork will squeeze harder against hte CD's.

If the axle spins inside the cork, you can try drilling a smaller hole in the cork or alternately drilling a hole through the cork and the axle and sticking a small nail or perhaps paperclip through the hole.

Hope that helps some.

[dang.kristie]

Thank you bradleyshanrock-solberg for the detailed instructions,
I am still confused about something though:

how is the cylinder placed on top of the vcr? Is it like that?
Are there 2 sets of wheels, or one?
[IMAGE]

Also, does the cylinder work as the pulley? Because instructions for me is the weight can drop no more than 10 cm. If it does, how do I wrap the strings? You lost me there

[Ivan]

Hi bradleyshanrock-solberg,

I cannot thank you so much for the very detailed instructions on this. I feel it a lot more easier now that you explained it a lot better. Thank you very very much for the advice on this.

[bradleyshanrock-solberg]

I wish I knew how you got that diagram on, it would be easier if I could draw. It is very hard to translate something visualized in your head to the same image in somebody else's head just with words.

You'll want four wheels, but the front wheels don't do anything but roll. I've seen tripod designs too (one wheel in front) but it's easier to keep it going straight with four large wheels.

In your diagram, the cylinder is off by ninety degrees. It should not be lying sideways on the car, but standing upright. You could also use something like a soup can, with the top and bottom removed with a can opener. That would be stiffer and stronger but might have sharp edges on the inside and wouldn't give the "flap" option for a more sturdy attachment. It might also be harder to drill or punch a hole through.

Likewise the "pen", that you drape the string and weight over should be parallel with the axle, above it. The way you drew it, it is perpendicular to the axle.

The overall positioning is about right. You want most of the weight over the rear axle, the axle that you're using as your power source. The front wheel and front part of the cassette is to keep it stable and help steer. I suspect it will be easily heavy enough to be stable with two wheels and an axle and the lever arm of the cassette, but if for some reason your cart does "wheelies" (front wheels lift up when you release the weight) you can just add a little extra weight in front to keep it all stable.

This whole assembly for the weight...there are a lot of ways to do it. I thought it would be simpler to use a frame already constructed (soda bottle cylinder) than to make it out of parts. Also you seem to be already heading down that route, eg using the VCR cassette rather than trying to build your own frame from scratch. It's a similar idea. Look around for something about the right shape and figure out a way to attach it that is easy but sturdy enough. At the scale you're working with (1kg weight, 10cm drop) glues might not be enough but wrapping it in enough duct tape or any kind of mechanical join (screws, bolts) should be strong enough.

[bradleyshanrock-solberg]

Hi bradleyshanrock-solberg,

I cannot thank you so much for the very detailed instructions on this. I feel it a lot more easier now that you explained it a lot better. Thank you very very much for the advice on this.

You're welcome. Just be aware that what I visualized in my head and tried to communicate probably won't work exactly like how I imagined. The real world always introduces extra challenges. I think the basic approach is sound, but I've never actually tried to power a vehicle by dropping a kg weight on it! It should work more or less like I described, but real world engineering is different from theory. Just as an example, what if dropping the weight causes the axle/wheel attachment to buckle? You'll have to figure out how to make that section stronger, wheels wider perhaps...something. If the weight just hangs there and the cart doesn't move, you'll need to
figure out a way to grease the axle better...etc.

You will need to put it together and experiment a bit to find the right way. I can't stress enough how important it is to just try it out and play with it. If you can get anything that rolls at all, you can then fine tune it to get the best score.

If my experience with similar projects is any judge though, a lot of students will never get a working cart. The difference between those who succeed and those who fail is usually how early they tried to get a basic car built. You need time to test it, to fix problems as they come up.

[dang.kristie]

Making pictures are actually really easy, I just use the paint programs and they give you shapes to work with

[IMAGE]
So would it be kind of like that? I get that, but where does the weight come into the design? There still needs to be a pulley, unless thats what the bottle and pen is for..but where does it drop to land on the cassette, and how to do you attach it to the axle and pen?

[bradleyshanrock-solberg]

ok, that's a pretty good image, although the "pen" should be higher up, not halfway down, and the perspective is tricky...it should be parallel to the axle.

The pen replacing a pully. While a pully is better from a friction standpoint, it is extremely complex. Adding a pully if you don't happen to have one lying around is similar to running the axle through a bearing sleeve instead of just drilling a hole through the cassette tape and letting the axle touch the plastic. While your friction is better, it costs a lot in complexity. Even if you have a pully you still have to figure out how to attach it. A pen you can just poke through the plastic (better to drill it if you can, for an even hole). Fallback plan would be a metal can, as the weight on the pen might pull down and tear or deform the plastic. If you get a clean hole drilled though, plastic is pretty sturdy on these scales.

A 1kg weight dropping is pretty powerful compared to the friction resistance. It should be sufficient to cause a string to slide over a smooth, round plastic surface like a pen and turn an axle (possibly greased or lubricated with graphite) against plastic. This is especially true because we don't really have to worry about long term wear and tear on the string or the axle or the cassette - aside from testing this will only have to run one or two times.

The weight goes inside the cylinder (I don't have a good sense of how big this weight is, width/length/height. this is one area where visualization can break down). It rises up as you wind the string, and drops down inside the cylinder as the cart goes forward. The string is tied to the weight, goes over the pen, comes down, goes through the cassette and is wound around the axle. (I'm not sure if it is good or not to attach the string to the axle, that's an area for experimentation. It worked when I did it with rubberband-powered cars but we also needed it to stop at a certain point, which is not an issue in this test...longer distance is better grade)

The connection between the weight and the axle therefore is the string. To work consistently the "pen" would need to be pretty flat (if it is tilted, the string will slide to one side, the weight rubbing against the wall of the cylender). Alternately you might groove the "pen" somehow so the string couldn't slide left or right even if the pen wasn't perfectly level (or wrap tape on either side of the string, getting a channel for it without letting it slide sideways) These little tricks are things you learn by doing. It might not be a problem at all or it could be a problem big enough to require more engineering.

[dang.kristie]

Ok I think I understand most of it, but what do you mean when you say

It rises up as you wind the string, and drops down inside the cylinder as the cart goes forward. The string is tied to the weight, goes over the pen, comes down, goes through the cassette and is wound around the axle.

The weight goes through the cart? How is that possible when in the end, the requirement is that the weight stays with the cart? Do I have to cut a hole in the cassette?

Also, is the pen suppose to be drilled through the entire can or just one side? Thank you

[dang.kristie]

Do you think something like this would be a good idea?
[URL]
I think the hardest thing with this though is to find a pulley and what to build it with.

[bradleyshanrock-solberg]

The weight drops onto the top of the cassette and stays there. This is especially likely as it is surrounded by a cylinder. The only hole drilled through the VCR cassette is for the string.

The pen goes all the way through the cylinder. There is no way it would support 1kg if it wasn't supported by both sides of the bottle/can. I think what may be wrong in your visualization is that you may be assuming the weight is outside the cylinder. The whole assembly is inside....string, most of the pen, weight.

It would work even better with a box-like shape instead of cylinder - more room inside and easier to keep stable when attaching to the cassette, but cans and bottles are common. I can't think offhand of a sturdy, hollow, light box-like thing of the right size that is just lying around the house.

If you guys had legos to work with all kinds of things are easier. The front wheels, for example. Lego wheels are great if they just need to spin around. There are lego attachments for round parts on axles too. 1kg is pretty heavy for legos but you could do a lot of the hard stuff with it. You'd likely want something else to support the weight, but maybe not if you made a big blocky cart. It would not be like those pictured in the link with narrow, high frame. The 1kg weight would tear that apart. But you could build a sturdy box-like container and drop it just like I've proposed here, with normal bricks.

Legos are very easy because they are designed to attach to each other, and you can build very sturdy structures if you attach a lot of holes to the pegs. A lot of what is hard in this project is the attachments.

[dang.kristie]

The only hole drilled through the VCR cassette is for the string.

Where is the hole at? Is it for the string to get attached to the axle then back to the pen?

Also, the string is only attached to one side of the set of back wheels correct?

[bradleyshanrock-solberg]

The string should ideally be attached to the middle of the rear axle, and to only one axle. You drill the hole in cassette over the axle, maybe slightly offset behind it and thread the string through the hole (the string goes from the back of the axle to the back of the pen, preferably straight up),

The front wheels are only for stability. Don't attach any power source to that axle. The wheel/axle assembly can be entirely different if you want, as long as something up front supports the cart and turns, but unless there is too much friction from a rotating axle in front, it's probably easier to use the same approach on both axle/wheel assemblies.

[dang.kristie]

[IMAGE]
So if the cassette was see through it would be something like that? Do you think you can draw a picture?

Building wise, what do you recommend would be better? I am kind of leaning towards the legos but I am not sure if there are wheels large enough and a base strong enough. I wouldn't want to go out and buy everything and have it not turn out

[bradleyshanrock-solberg]

Are legos allowed? I would check with the teacher, they might fall into things not in the spirit of the challenge. If you don't already have them, the number of bricks you need to do a cart this sturdy might get pretty expensive.

With respect to the diagram....the pen is higher up, near the top of the cylinder. The string isn't wrapped around like you drew. Go to the beginning of the thread and look at the pully diagram Ivan added. It works like that. Weight on one side, string up into pully, down out of other side of pully to the axle. No circular loops. Just like that except the pen supports the string instead of the pully.

The only thing the string is wrapped around would be the axle.

[dang.kristie]

Wow ok I think I FINALLY get it!

[IMAGE]

From an odd angle, it would be something like this correct?
Thank you very much! I will work on it tomorrow after school and tell you how it goes!

[bradleyshanrock-solberg]

Yes, that's right, that's the basic idea.

Making it actually work is an exercise for the student.

[Ivan]

Wow ok I think I FINALLY get it!

[IMAGE]

From an odd angle, it would be something like this correct?
Thank you very much! I will work on it tomorrow after school and tell you how it goes!

May you send me the image of your final product? Not the cart but the design. For some reason I used to see it. Now cant.

[shiftcomma3]

Hi(: I know it's very late to start on my project -- things have been tough and crazy so my partner and I could not have started on it any sooner than now
I'm not much of a...builder. The concept of machines just don't make sense in my head.
How would you get all the pieces to stick together? hot glue?
Would using a plastic container as the body work well?
I read all of the responses and i see the thing about the wheels being cd's and using a cork to grip.. how would the wheels be attached to the car?
Would a lever system or a pulley system be better?

All of this is starting to make me panic
Thank you so much
I know you must be tired from helping out everyone on here already

[Ivan]

Hi shiftcomma3,

It depends what you are going to do. Hot glue sounds good for sticking pieces. Here is what I did.

I cut out 2 different pieces of straw and glued them on the front side of the cart (Right Front and Left Front). Then I got like some good strong stick (not to strong but ok)and stuck it thru the straws. Once it reaches the end cut out a necessary length. So now you should have a piece of stick through both straws. Then got 2 CDs glued them together to form a more thicker wheel. So I did that and got a bottle(Milk, Juice cap and glued it to the front of the wheels. Make sure it covers the hole of the CDs. Now what you do is poke a hole in the center of the cap. Then you insert the Wheels through the stick and make sure that the stick go through the whole of the cap. Once it is there, glue the cap to the stick. I havent gotten to the part of the pulley. I dont know about the body. You can try it but make sure its not too heavy nor too light. Good luck.

[shiftcomma3]

Hi shiftcomma3,

It depends what you are going to do. Hot glue sounds good for sticking pieces. Here is what I did.

I cut out 2 different pieces of straw and glued them on the front side of the cart (Right Front and Left Front). Then I got like some good strong stick (not to strong but ok)and stuck it thru the straws. Once it reaches the end cut out a necessary length. So now you should have a piece of stick through both straws. Then got 2 CDs glued them together to form a more thicker wheel. So I did that and got a bottle(Milk, Juice cap and glued it to the front of the wheels. Make sure it covers the hole of the CDs. Now what you do is poke a hole in the center of the cap. Then you insert the Wheels through the stick and make sure that the stick go through the whole of the cap. Once it is there, glue the cap to the stick. I havent gotten to the part of the pulley. I dont know about the body. You can try it but make sure its not too heavy nor too light. Good luck.

I've got the wheels done differently and it seems to work fine
i'm going to this plastic basket that i've got, which has like pattern of squared holes so it will easy to attach the wheels on
i'm not really sure about the pulley either
but from reading the other posts, i'm guessing i'll be trying out the plastic bottle thing that the others were talking about previously...
i'm working on it tonight with my partner.

my teacher, ms. sosa. is driving me nuts

[Ivan]

What do you know? You and I have the same teacher. What period are you and whats your name?

For the pulley. I got a reel and supported it.
Anyways Good luck on your project.

[shiftcomma3]

i have her 3rd period
thanks
its...failing right now :[

[bradleyshanrock-solberg]

Given her grading scheme, you're best off turning in whatever you have than not anything.

If you make a good shot at it, she gives you 60 points. This kind of thing will usually not work
the first time you build it, it takes tweaking and learning to get it really functional, and that takes
time. Which is why I recommended an early start at the beginning of this thread even if you do
not understand everything.

[Ivan]

Hey guys. First off I want to thank you all very much for the advice and help you gave me. The cart moved about a meter and something but really close to 2 meters. But we have to get it to 2 meters for 80 pts. She marked it as a .5 and gave me and my partner 70 pts. . Anyways here is things that I have noticed today.

We were not testing in a leveled surface. When the cart stopped, the cart moved back about 5-10cm. I was questioned. So we did it again as a retrial. Still the same thing. It moved back. A bit disappointed on the results (not my partners,cart, or my fault. We did the best we could.) So it was over. I still did some testing though to see if the surface was uneven. I did it in the opposite direction. The cart did not move back. This was enough to prove that we were not on a leveled surface. So I went to another area nearby. I tested it on each direction. Guess what? Each direction had very similar results. What do you guys think?

[vishwa]

Ivan,
All of the suggestions in this thread have been excellent and you are doing a great job trying to complete this project. I just wanted to add one little thing, and don't think it is disallowed (looking at the rules) - please ensure that the floor (i.e. the path along which your vehicle would traverse) is "polished", i.e. try to see that it offers as minimal a resistance to the movement of the vehicle as possible, since every cm counts. If the actual demo is to be conducted on a rough surface, please ensure that it is free from "debris" to the maximum extent possible.

[Ivan]

Hi vishwa,
If I can take this experiment on the different leveled area, I would. But I have no control of where the experiment is held at. My teacher told us to do the experiment on the unleveled surface. I dont think she knew about it though. In another way, I think she does.

[bradleyshanrock-solberg]

If it's any consolation to you when I did a project like this roughly 20 years ago, after a week of testing when it came time to actually run the test I was nervous and wound it up a little extra...which caused it to go too far (we had to stop in a specific area). Then the wheels spun as it went of the table and I lost the calibration on the retry, doing even worse. I still got a half decent grade but like you missed out on the best score due to operator error. At least you have a better reason! (the environment not being what you expected)

The important thing is that you built imagined something and built it and it basically worked. Perhaps not as well as you hoped but you did the hard part. Given more time to refine and test the design you likely would have done better.

A big part of the lesson in this kind of task is that nothing ever works exactly like you imagined it would, and deadlines often come before there is time to work out the best approach. This is a lot like real life engineering, and the best you can do is to try to gauge the risks at the beginning and plan accordingly.

I'm glad you built the thing, and that it moved. That's a big accomplishment by itself. Don't get too hung up on the exact score you got - you probably learned more about real world problem solving in this project than you're likely to learn the rest of the year in school.