We had access to lots of donor bike parts from a local alternative transportation group. Follow the link below to see how you can get similar parts.
This Ible describes the prototype for the cargo trike that followed. I am working on an Ible describing the next version of the cargo trike we have built. I will add a link to that Ible when I get it published.
Prototype Cargo Trike Specifications:
Overall weight 75#
Cargo portion with front wheels 48#
Rear portion with rear wheel 27#
Cargo Bed 30" X 48"
Pivot Pin 24" from front
Front wheel axles 27" from front
Handlebar is 30" above the bed
Step 1: Selecting the Rear Power Wheel
Step 2: Designing the Pivot Pin
We decided to keep things simple in the prototype. For starters the pivot point would be kept vertical - there wouldn't be any fore-or-aft pitch to make the trike lean in turns. This is simpler to build, but it means the rider has to lean into (toward) the turn to help keep the trike upright.
Next we decided to use off-the-shelf parts for the pivot in the prototype. We purchased two 1/2" gate hinges and a 1/2" X 6" bolt at Tractor Supply Company (TSC). Photo #1 shows the hinges and bolt before welding.
Step 3: The Cargo Bed
We decided to build the cargo frame out of EMT conduit even though there is some health issues when welding EMT. Follow the link below for some safety tips.
Step 4: Rear Fork and Linking Tube
This proved to be one of the weak points of the prototype because the linking tube was not strong enough to prevent flexing and torsion along its length. There is a lot of leverage from the seat tube and saddle along the length of this part of the main frame and we still don't have a good design for this part.
Photo #4 shows the "foot brake" on the linking tube and the shift lever located on the seat post.
Step 5: The Handlebar
This was eventually cut off and replaced by what is shown in Photo #2. The width (30") is fixed, but the height (30") is adjustable. The top part is 1/2" tubing which slides into two vertical 3/4" tubes welded to the cargo bed. A couple of pins hold the handlebar tubing in place.
Step 6: Performance Review
The power wheel and seat worked fine. The cart was easy to ride. You do need to lean into the turns or the trike will tend to tip outward. The tipping could be more of a problem if the load had a high center of gravity.
the handlebar was in way when standing up to pedal up a hill. The next design will have two separate hand grips to either side.
The pivot pin and gate hinges worked OK. A stronger cross piece on the cargo bed would prevent some of the side-to-side flexing. Commercial cargo trikes usually have reinforcing tubes that stabilize the lower end of the pivot.
All things considered this was a fun first cargo trike from which we learned a lot. (Note: The cargo bed and wheels are now serving very nicely as a garden cart.)