Motor + Sprocket Mount
To fit out sprocket to our motor, I needed to drill out the sprocket to 8 mm to match the motor shaft. I then decided (after much deliberation) to use set screws – I haven’t had good experiences with them in the past, and I definitely don’t want set screws detaching for such an important part as a motor and sprocket. But I decided to make this set screw larger, 10-32: more surface area for contact. So we got set screws (90289A337 on Mcmaster). I then drilled and tapped a hole on the sprocket for the set screw.
Lastly, I keyed the shaft on the motor to provide a flat for the set screw (never use set screws without a flat).
I did all this machining at the Edgerton Shop, an awesome shop open for students on campus, as they had larger milling machines than the IDC. [pictures] I came back with the motor and tried to assemble everything. The motor mount conflicted with the 80×20…so I dremeled it down. So Dremel. Much fun. Wow. It was pretty fun.
Then, sad problem. When I assembled the motor, I realized that because we had changed the dimensions on our plates for holding the motor (because they had worked in the CAD but not in real life), the little sprocket could not fit onto the motor shaft and also line up with the larger sprocket. It was off the shaft by approximately 0.4 inches. I was dejected as it means we can’t use the original motor plates to hold things together…adding 0.4″ will mean it won’t line up with the 80×20 pieces. But I really wanted to test everything else about the motor, so I cut a new piece of 80×20 and attached it with the original pieces by, well, taking advantage of the fact that there are 2 sides to attach things to. As you can see in the picture below, the top hole doesn’t match the 80×20. I also took a bandsaw to the useless part, as it conflicted with the motor mount.
After that, I could attach the motor, put the chain and sprocket, and proceed to design a tensioner, now that I could see everything by eye.
Brake + Flipping our Kart:
After happily spinning the wheel and seeing it work, I suddenly realized that our brake wasn’t working anymore. It had unscrewed itself because brakes have a preferred direction (thanks Jamieson!), and if you spin the wheel in the other direction, the band brake screws itself off. Good thing we realized this before installing everything permanently. So, we needed to flip the direction of the wheel so that when we drive forward, we can keep our brake screwed on. Instead of taking everything off, I realized I could just flip the kart upside down and then reverse the seat mount – that would solve all our problems. So our new kart looks like this:
Also, I got more of an idea of how to put our brakes in place (thanks youtube) but I can’t cut the wire and housing until the steering is in place, so that’s tabled a bit. Brakes are definitely a priority, though, because it’s on the checklist of Milestone 7. I took a hand brake lever off a bike.
Our motor is movable, so that in itself could act as a tensioner. But because we only have 11 teeth on our small sprocket, we decided to design a tensioner that allow the chain to contact more teeth. I CADed out a tensioner . The spring and the screw are quickly represented by cylinders in the model. We will waterjet the tensioner frame (which simply holds the spring and the tensioner at a correct height) and the tensioner bar, which is pushed down by a compression spring. I also designed the tensioner piece to be exactly the same as our sprocket, so it will work with the chain. I also ordered longer 1/4-28 screws (2 inches).
Front Plate, Steering Wheel+ PhoenixKart
Aisha designed the front plate that will go on the front of our kart, act as a footrest, and hold the accelerator. Early on in our brainstorming process, we decided we wanted a theme for our kart. We decided on
road-kill kart phoenix kart, complete with phoenix steering wheel and a footrest that looked like flames. Artistic Aisha used splines to CAD and then lasercut the front plate and worked on the steering wheel. Pretty, isn’t it? Though to prevent us from impaling ourselves on our kart, we’re going to have to make the steering wheel / front plate less pointy. Don’t want to kill anyone either.