Talk:Report 2: Research, Opportunities and Concepts

From DDL Wiki

We received your second report, and you have some interesting ideas. You mention that you are targeting environmentally aware consumers – if this is your target market, you should be sure to be able to determine that your product is environmentally better (will it require more waste in production, even if it does not require new batteries? How often must rechargeable batteries be replaced? Etc).

It looks like you need some analysis to determine dynamic torque loading on the rider (is this negligable?) as well as current required for brightness, current capacity of components (battery, etc). Your power storage concept is a nice idea. This will require analysis of components (voltage regulator, battery pack) and design of circuit (“chip”). The closed circuit idea is straightforward and easy to implement. The power button and charge indicator are also straightfoward components to add, but packaging design and component selection will require some analysis. It’s not clear how the different mount concepts will make electrical contact for positive and negative sides. The chain-mounted generator is an interesting idea – the sketch needs to be more flushed out, and you need some analysis to show if there is an advantage to running the generator off the chain. If it is only to avoid water and mud, this could be reason enough – but bottles may do this as well with less complexity. If you are trying to limit the maximum voltage to the circuit, more analysis is needed to determine if this is necessary or even advantageous. The turn signal concept is also a nice idea – you would need to work out mounting as well as actuation (interface) and the circuit. The final magnet concept is very promising, but you need a preliminary analysis to determine how much power can be generated this way and if it is enough to produce sufficient light. Also, there are significant dynamics issues – will the motor turn over fast enough before the next magnet passes by when the bicycle is at high speed – should this be mounted on the main sprocket?

Your Pugh chart is interesting, but what are the conclusions? We couldn’t find your recommendations about which concept(s) to pursue.

In short, you have some good ideas, but the back-of-the-envelope engineering analysis to determine feasibility is missing, and it is difficult to determine which concept to pursue without this analysis. Our recommendation is that you first run a quick analysis of each option to determine feasibility. Assuming all options are feasible, we suggest that you follow one of two paths:

• 1) If you can show the clear advantage for a chain-mounted generator, this is the option that your skill set is most tuned to address. This would require more detailed conceptual exploration to determine appropriate linkages to keep the generator with the chain as the rider changes gears – it seems that you do not have this worked out yet. You would then need to move quickly into detailed design and analysis to determine appropriate chain tension and placement/orientation for all gear combinations as well as output power characteristics. You will also need to determine the drag characteristics on the rider, both theoretically and through testing.
• 2) If you can show a clear advantage for the magnetic generator and assess feasibility in terms of cost and electromechanical characteristics, the main challenge here would be to determine appropriate placement and mounting design and to analyze the electromechanical dynamics and determine when the speed will be too fast for the motor to design it appropriately. You would also need to determine analytically and through testing how much speed is needed to start the light and how long the battery holds a charge (what happens in the first minute of my night ride if the bike has been sitting beforehand?)
• 3) The third option is to integrate concepts 1, 2, 3 and 5 into a single design, working out all details of circuit design, mounting for a variety of bicycle configurations, and interface with the turn signals as well as battery life. This option would require more study of electrical circuit design and selection of appropriate components based on required characteristics. You would want to consider the option of using a capacitor in place of the rechargeable battery to determine which is more appropriate, and you will want to determine how quickly a typical riding profile would burn out a battery (with the resulting dynamic state of charge).

We look forward to seeing your prototypes in the design review.