By Renaud Anjoran
Last week I posted part 1 of our series on What It Takes to Develop a New Electronic Product in China.
In this second part we look at R&D and at the evaluation of power consumption.
1. R&D (both in-house & with a manufacturing partner)
1.1 Functional and System Development
Research and development involves a lot of work that is typically split between your in-house capabilities (if you employ designers and engineers) and your supplier capabilities.
One one extreme is a company like Apple — they go to their contract manufacturers with a prototype already fully designed and spec’d out. On the the other extreme is the non-technical founder of a ‘hardware startup’ who needs a Chinese supplier to do the R&D for him so that he can sell a first batch on Kickstarter/Indigogo. Not every company has the facilities in-house to carry out testing or to build various development testing fixtures/apparatus!
In any case, it is generally good to get your supply partner involved at this stage, as they are the ones who will be manufacturing the product and generally have deep knowledge of manufacturing processes.
Take the drone product described in part one of this series. Your supplier may be in a better position to carry out some of the research and development of some features and sub-assemblies from a system point of view than you are.
The figure below shows a simplified R&D cycle for such a complex product. The design would be built as a prototype, potentially into sub-systems then tested.
Typical tests are failure threshold tests, optimization of operating windows and system integration tolerances, etc. Some very advanced companies might use DOEs (Design of Experiments — a systematic method to determine the relationship between factors affecting a process and the output of that process, in order to manage process inputs and optimize the output).
In theory, this cycle continues until the design has been optimized to the point were further development of changes would not be beneficial to the product. In practice, it also depends on the company’s budget and on the Chinese supplier’s motivation!! Many companies run one iteration, get workable results, and get a first batch into production. Iterative improvements often have to wait for future batches.
1.2 System Integration
As part of the overall product functionality, there are several different sub-assemblies or systems that work both independently as well as having to work as an overall larger assembly once built into the final product. Take the capture device launcher as an example, this could be designed, developed and tested independently from the security breech alerting system. The capture device launching system could be developed by you and your supplier concurrently through online collaboration tools and shared designs. This not only allows for more expertize to work on the project but can also accelerate the design process.
2. Power Consumption Evaluation
On a complex product that consists of various elements that require power to drive some sort of device, it is paramount that the power consumption is calculated at both element and overall system level.
If we look back at the system chart there are a number of obvious elements that require power and some of those elements will require more power than other. The large drone stands out as being the main power consumption element. Power distribution and safety controls would also need to be considered during this initial evaluation phase.
One of the key aspects of evaluating the power consumption is to understand the required power and in most cases this means understanding what batteries are required. During the battery evaluation, not only should the amp-hours (Ah) be considered but also the type of battery (size and weight as all these factors will play a big part of the overall product design).
A battery pack’s capacity is measured in amp-hours (Ah). Small battery packs can be in the range of 0.1Ah (100mAh); battery packs for medium sized drones are 2-3Ah (2000mAh-3000mAh).
The higher the capacity, the longer the flight time, but the heavier the pack will be. You can expect the flight time of a normal drone to be in the order of 10-20 minutes, which might not seem like a long time, but you need to consider it’s always fighting against gravity, and, unlike an airplane, there are no surfaces to help with lift.
When it comes to our interceptor drone, it will also include the capture device and firing mechanism, which needs to be taken into consideration during the calculations.
To show an example calculation we have taken this from the following article: http://diydrones.com/forum/topics/calculating-battery-usage.
To estimate your flight time (quite precisely in fact), the formula is:
- Take your drone weight, divide by the number of motors — you get thrust needed to hover per motor
- Multiply this number by 2, it gives you max thrust needed for effective braking and recovery maneuvers (to choose the right motor for your machine)
- Make a bench test with motor at hover thrust and note power consumed (W)
- Divide power by nominal battery voltage (3s = 11.1V, 4S = 14.8V etc…) — it gives you hovering current per motor, or Hc(A)
- Divide battery capacity Bc(Ah) by (Number of motors x Hc(A)) and multiply this by 60 (minutes)
- Then, multiply this number by 0.8 (20% loss of efficiency)
The result is the estimated flight time for hovering or gentle flying.
- The drone is 2,000g, so you need 500g thrust per motor on a quad style drone (and your motor needs to be able to give roughly 1,000g thrust at full throttle)
- You calculate you need 55W per motor, that gives you roughly 5A with a 3S LiPo
- Your battery is 5,000mAh, so that’s 5Ah
- You divide 5Ah by 4 x 5A and multiply this number by 60 = (5/20) x 60 = 15 minutes
- Then, multiply this number by 0.8 and you get 12 minutes
Once you know these data points, is it easy to work out the power requirements for our drone example. Don’t forget to look at all the other aspects of the design when considering batteries and power requirements.
Renaud Anjoran has been managing his quality assurance agency (Sofeast Ltd) since 2006. In addition, a passion for improving the way people work has pushed him to launch a consultancy to improve factories and a web application to manage the purchasing process. He writes advice for importers on qualityinspection.org.