2.007 Milestone 6: Making an MDF-kart

Redesigning the kart rear wheel drive + mounting:

Aisha and I spent a frantic Friday solidworksing and Arduinoing (for physical homework #6 – program a motor controller!

I realized that I had designed a back wheel mount that was lower to the ground but it didn’t match the design for the front wheels. Oops. Here is our new design! I put in plates similar to the the ones we had for our front wheels to hold the back wheel in place. We also decided to mount our electronics in the back of our kart (as seen here!)

motor electronics back design

Kart with Person
Kart with Person

Prototyping and Building our Kart out of MDF

On Saturday / Monday, we went in and prototyped our kart. We lasercut the joints / pieces out of MDF and cut the 80×20 into our frame pieces with the cold saw.

2014-03-14 23.18.27

Assembly assembly assembly

2014-03-15 00.23.10-1
Frame!
2014-03-16 23.37.16-1
Wheel Mounts + Rear

A Lesson on Designing for Assembly

When designing, it’s important to think about the order of assembly and the easiness of assembling it. In Solidworks, everything can assemble fine, but in real life, it won’t work the same way. This lesson was duly learned when I sadly tried to put together the MDF-kart and it was hard to screw in the wheel mount nuts.

old motor mount
Looks beautiful in CAD
2014-03-16 23.37.47
Cannot actually tighten this; can’t reach my fingers in 😦

We’re going to redesign this.

Rules, Deadlines, and Organization:

The milestone 7 deadline is looming closer – by April 1, we need to have a rolling frame done! That means it needs to be able to roll, brake, have a person seated, etc. Here are the requirements:

1) The frame is assembled and can support weight without unreasonable flexing.

2) Mechanical subsystems such as steering, braking are mounted rigidly and do not wobble, flex, or move with interference such as scrubbing or scraping.

3) The vehicle can roll freely without mechanical interference in the drivetrain

4) From a jogging-speed push, the vehicle is able to lock up its braking wheel(s); the vehicle’s braking force exceeds available traction.

5) The motor is mounted rigidly with fasteners, but not necessarily connected to the drivetrain.

6) ll provisions for hooking the motor up to the drivetrain are finished (e.g. pulleys are properly bored and mounted, tensioners and retainers mounted)

7) Fasteners are properly used and installed  (e.g. all screws and bolts tightened, bolts are not used in shear, standoffs and spacers are not made of stacks of washers)

8)  No portions of the frame are bent or forced to fit an assembly – all machined and fabricated components fit true and square, or as-designed

9) All materials used in the vehicle are final and documented in the Bill of Materials. No prototyping mat’ls (e.g. class-supplied wood) or “tape and zip ties” construction is present.

10)  The final seating or riding arrangement is present.

This is a lot for 2 weeks! Considering we have yet to order a few parts (namely brakes and fasteners) and shipping (when will our ebay seat get here?!) it’s a bit worrisome. But we’ll be able to do this! Also, out of the next 2 weeks, one of the weeks is my hell week and the other week is spring break. Aisha and I will likely be spending our spring break in the IDC. However, we do need to get a lot of things done this week, especially because a lot of things take downtime – shipping and waterjetting take time. Since we’ll be building a lot in spring break and Charles cannot officially encourage building, we won’t be able to order parts / waterjetting that week, so we’ll need to order everything now! So, we plan to have all our waterjet components finished and formatted this weekend, as waterjetting takes 1 week of time to deliver :\, and we plan to order the rest of our parts. We’ve definitely come a long way!

Making a tensioner:

As mentioned, we need to make a tensioner because our sprocket has too few teeth.

Research on the internet: http://machinedesign.com/archive/belt-and-chain-tensioners

I was thinking about simply screwing on a tensioner, but since the chain stretches and produces oscillatory movements, most tensioners you can buy have springs to damp the vibrations. That’s why many tensioners have a lever arm to automatically tension the chain.

We tried this design first:

Motor Mount Front Face

Next Steps

We are submitting our finalized waterjet pieces and BOM on Tuesday. Hopefully this is all that is left! After Friday, Aisha and I will begin building, and hopefully, we already have all our pieces. The final step to fulfil Milestone 7 is assembly and after that, electronics.

Next post

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