Lay-down Farming Cart to Help With Back Pain (a.k.a. the Cropadile)

*Part of the GEEN 2400 class for CU Boulder*

Many farmers have back issues due to bending down to pick lower crops or weeds. Our small student team came together to create a solution to these back problems: A lay-down cart. Other solutions exist to this problem though the cheapest one costs $6000 and requires an electrical hookup. Our goal was to create a cart using materials that were accessible and cheap so anybody could build their own. We wanted our design to be as simple as possible and not require fancy electrical components so that the individual could modify it for their purpose. These steps are tailored to one specific farm, for different weight specifications or wider crop beds the design can be easily adjusted.

To download SolidWorks files please use this Link.

https://drive.google.com/drive/folders/1ml0HMgwzxouhzEB69KkUB8jN3aq9Tc1C?usp=sharing

Supplies

Materials Needed

4x) 2x4 Wood 8' long ~ $10

1x) 2x8 Wood 9' long ~ $12

30x*) 3/8" Tee Nuts ~ $15

4x) 3/8" Locking Nuts ~ $3

24x*) 3/8" Washer ~ $10

12x*) 3/8" Bolt 7" long ~ $34

12x*) 3/8" Bolt 4" long ~$21

2x*) Old/Scrap bikes ~ $30

1x) Painters Tarp large ~ $20

Total Estimate ~ $155

Tools Required

Miter saw - Wood blade

hand drill or drill press - standard size bits, hole saw kit, spade bits

sawzall - metal blade

*There are 2 ways you can build this cart: the way we have demonstrated using only 2 bikes, and a more simple version using 4 bikes. The 2-bike way although more cost-effective is more difficult since you need to cut the back fork from the frame of the bike and attach that to the frame of the cart. If you feel confident in your handy skills then we recommend the 2-bike approach. But if you aren't certain the 4-bike method might be better for your needs.

**This is using the 2-bike method, for the 4-bike method you need 32 of each.

Step 1: Create 2x4 Frame

The body of the frame is made out of 2x4s, to hold a person over 200lbs reliably it might be smart to use 2x6s.

For this step, we must determine the dimensions we want for the frame.

The dimensions our group used are for a man of average height (around 5'10") though if you are shorter than 5'4" or taller than 6'2" you might want to consider adjusting the length of the side 2x4s. The top and bottom 2x4 sizes should depend on the width of the crop bed and the path. The bed we based our design on is 4' center-to-center; we recommend making your 2x4s the same length as the center-to-center distance. This is best done with 2x4s with as little warp as possible

So as shown in the Solidworks screenshot create a frame of similar dimensions using:

2- 2x4s cut to 48"

2- 2x4s cut to 78"

This can be done with many different tools but a chop saw or miter saw is the easiest

Step 2: Create Connecting Brackets

This is maybe the most important and difficult step of the entire project!

The brackets are the most important structural component that both hold the frame together but also allow the front bike forks to easily slide into place. These can be made using 2x6s or larger, we used 2x8s and would recommend using that too. (For the 2-bike approach you need 6 brackets, and for the 4-bike approach you need 8 brackets.)

1) Cut 2x7s - Cut the 2x8s into right isosceles triangles as shown in the CAD image, so the short sides should measure 6.5" and the hypotenuse should be ~9.2" (2-bike needs 12 triangles, 4-bike needs 16 triangles)

2) Glue Pieces Together - Glue 2 triangles face to face using your wood glue to create one triangle with a depth of 3" repeat for all triangles until you have the correct number of brackets

3) Drill Center Hole - The center hole of the bracket should be as similar in diameter to the bike fork as possible. In most cases that would be 1.125" but it might be best to do step 5 and disassemble the bikes first to be certain of the size needed. Either way, you will need a hole saw to cut a hole this large, though the bracket is now too large to create a hole all the way through with a hole saw. What we found was easiest was drilling a pilot hole of about .125" all the way through using a standard wood drill bit. Then using that pilot hole you can align the hole saw on both sides, drill one side then switch to the other to create a complete hole.

4) Drill Side Holes - Now the side holes are a little bit more complicated. To start you either need a 6" long drill bit or need to be very careful with where you are drilling. If you are looking at the hypotenuse of the triangle the holes on one of the 2x8s should be perpendicular to one of the right angle sides, the 2 holes on the other 2x8 in the bracket should then be perpendicular to that as best shown in the photos. Start by using a .375" drill bit to drill the shorter holes. There is no exact location to drill these but it would be best to make sure they are in the middle of a 2x8 and still have enough material to be strong. Then you can use a 6" drill bit to drill the much deeper holes, though if you don't have access to this bit you can carefully drill as deep as possible and then drill from the other side and try to meet in the middle. Once the main holes have been drilled you can use a large spade bit (we used .875") to create a flat surface for the head of a bolt to pull on, you could probably use a large regular bit though this wouldn't create as flat of a surface but this could be combated with 2 washers. This is hard to explain and is best represented through the CAD models and the pictures.

5) Sand Bracket - Next you can sand down the outer faces of the bracket to get rid of any misalignments you might have using either a belt or hand sander.

Finally, ensure the bolts you bought fit through the holes you drilled and stick out on the other side with about 1.5" extra

Step 3: Assemble Frame

Now you can use the brackets to connect all the 2x4s together. We didn't have any pictures of the brackets on the frame without the front bike fork, so just ignore that in the pictures.

1) Line all 2x4s into the proper position on the ground and place a bracket in all of the corners but the two bottom outside ones (this will be much easier to keep track of if you label every 2x4 and bracket with a symbol so you know how they line up)(for 4 bike design add a bracket to every corner).

2) Once everything looks like the CAD model pictured you can use a pencil to mark where the holes in the brackets line up on the 2x4s. Then once marked you can drill a hole in the 2x4 using a 1/2" drill bit.

3) Then put the tee nuts on the outside of the new holes in the 2x4s, add the bolts and washers to the brackets, and connect all of the inside brackets.

4) After inside brackets are added the bolts should stick out a little bit and this can interfere with the outside brackets so use a sawzall or hacksaw and cut off the ends of the bolts

5) The outside brackets might not still lay flat, use a very large drill bit to make small indents in the area where the bolts are contacting so they can lie flat on the frame. Then attach the outside brackets

The frame should now be very sturdy. This step is very easy to make mistakes in so make sure to measure twice and cut once so your cart lasts as long as possible.

Step 4: Create Hammock

For the hammock, you will want to choose a material that is strong and durable. For this, we chose painters tarp, since it meets those requirements and is easy to access. The hammock is pretty easy to create and attach, though keep in mind it will sag more and more over time so you will want to adjust it after a little bit of use.

1) Cut the hammock to the desired length - To do this you should measure the width of the cart and double that, then +12" and that is the width of the hammock you want. The height of it can be anything you want that fits in the frame (note it should be about 12" from the head of the frame and 12" from the foot) this means our hammock was 108" wide and 54" tall.

2) Double the hammock - To make sure the hammock can support the weight of a person you should double the width back on itself so there are now 2 layers of fabric and it is 54" wide and 54" tall. We opted to sew this folded section together to make it sturdier but you should be able to tape it or it should just be fine when you staple it to the frame.

3) Attach to Frame - Now to attach to the frame it is easiest to just use a staple gun though you could use roofing nails or something of the like. You can fold the sides of the hammock over the frame and then staple it to the underside with a liberal amount of staples.

4) Create a headrest - Finally, for the headrest you can repeat the last few steps but with a much smaller piece of fabric. We didn't double it up since it doesn't have to hold as much weight and we used a 6" long strip. We then stapled it to the head and sides of the frame.

Unfortunately, we didn't take many good photos while working with the hammock, though you can see the design in the completed image

Step 5: Disassemble Bikes

There are 2 main parts to disassembling the bikes. If you are doing the 2-bike design you need both parts but if you are doing the 4-bike design you only need the first part (this is where the designs become significantly different).

Step 1 - Get Front Fork: I could describe how to do this step but it would be difficult and confusing for you. This YouTube video explains how to do it far better: [ https://www.youtube.com/watch?v=0QlDq35lohw ]. You only have to watch to 1:06. From this you will need the front wheel and the main fork that the wheel directly attaches to. Any other parts are not necessary.

Step 2 - Get Back Fork: This step is a lot more in-depth and requires cutting the frame of the bike (this is why the 4-bike design is easiest).

1) Start by removing any parts attached to the back wheel or back fork (back fork reference image attached), this most likely includes the brakes, derailer, and chain.

2) After you have detached the extra parts you then have to take off the pedals and crankset (This is the most complicated part of the whole process as you need some specialized tools, you can watch YouTube videos or just go to your local bike shop and they should do it for you for very cheap). Now you should have just the frame by itself as shown in the 3rd photo.

3)Use a sawzall with a metal blade to cut along the red line as close to the post as possible. Now that it is cut you should have the back fork

Reattach the wheels back to the front and back forks and now you're ready to attach them to the frame of the cart and get it all moving!

Step 6: Connect Bikes to Frame

Finally, you have to attach the bike forks to the frame. You're nearly done!!!

Step 1 - Attach Front Fork: This step is fairly easy and also the only one you need if you are doing the 4-bike design. The front forks should slide cleanly into the main holes cut in the brackets. This still allows the wheels to turn and since we are picking crops in straight beds we don't want that. To solve this we used a hand drill to add small holes to both the bracket and the front fork so we could add 2 pins in each fork to keep it from rotating. For this we used scrap metal, though you can use more bolts or whatever you please. Then you can hammer the pins into place and the wheel will feel far more sturdy.

Step 2 - Attach Back Fork: Lastly, the final step in the 2-bike design is attaching the back forks to the frame. This step isn't easy and shouldn't be overlooked. To start drill 3 semi-evenly spaced holes in the main post part of the back fork so that bolts can connect through the fork to the frame. Then very important you add a spacer piece of wood since the tube that the crank used to be in extends out further than the post tube and would cause the wheel to not be parallel to the cart. you can either carve a back fork section out of a 2x4 as shown in the photos or you could just use a small piece of plywood, either would accomplish the same thing. Then line the fork up to the frame how you want to attach it and drill holes in the wooden frame so you can connect them using the bolts. Though this is attached the back fork it still has some wiggle when weight is applied. To combat this you must use a general drill bit on a hand drill to drill straight through the frame and through the crank tube then use needle nose pliers to add the locking nuts inside the crank tube with the head of the bolts on the outside of the cart. This should fully solidify the design.

Congrats you have now built your very on lay-down farming cart!

Step 7: Test

Now all you have to do is jump on the cart and give it a good test. It is easiest to just grab the front 2 tires and move yourself like you would in a wheelchair. We think the genius of this design is how simple the whole thing is, if you want to add shelves for storage just screw in a few 2x4s and plywood. If you want hooks for 5-gallon buckets just add that to the frame. Or if you want to implement a pedal movement system, or keep brakes on one of the front tires, or add a sunshade using the rest of the painter's tarp you can do it. This cart is perfect to expand and build on.

And just like that you have now created a cheap and easy-to-use, store and replace farming cart to help alleviate your back pain.