The Impact of the ASTM Standard on Batteries and BMS on Drone Programs
The beginning for drones in the form we know today goes back to WW II as the Denny
Radioplane. Batteries have always been the heart of the system.
As a point of reference, the UK and US converted manned aircraft to be radio controlled after WW I.
Fred Marks’ late friend Dr Walt Good and his twin brother, Dr Bill Good developed radio-controlled model airplanes in the 1930s as part of their doctorate program. The Denny Radioplane was the early entrant to R/C drones for military application – as aerial targets in 1941. Battery requirements were driven by the fact that transistors had not yet been invented. The only source of power for tube control was the dry-cell; up to 185V. 1.5V dry cells powered escapements or motor-driven actuators.
In 1959, Walt was an engineer with John’s Hopkins Lab near Baltimore and had access to the newest battery technology. He surprised the R/C hobby by making the first use of the Yardney Silver-Cadmium (SilCad) cells for motor driven actuators and this resulted in a quantum jump in reliability. After meeting Walt in 1959, Fred Marks, Founder of FMA, Inc. took up the R/C hobby, by which time the nickel-cadmium (Ni Cd) cell had overtaken the costly Sil Cad.
Ni Cads were the choice until 2002.
For 40 years, Ni-Cd cells were not really challenged in the R/C hobby as transistors and integrated circuits permitted operation of the radio link as well as actuators and servos, usually at a nominal 4.8V(4S Ni-Cd). During that period, Fred Marks “moonlighted” as the designer for ACE R/C and wrote books on the subject of R/C. In 1982, Fred made the transition from a 25-year career in aircraft and drones (Fairchild F-27A and the 12,000 lb AN/USD 5 drone) to satellite communications to weapons systems (F-14; Multiple Launch Rocket System [MLRS]) to full-time development of R/C systems and the semi-scale FQM-117B Mig 27 aerial target. Over 100K of that target produced and flown world-wide
carried a 6V Ni-Cd pack. Battery pack life was not a great concern since the average target was shot to pieces in less than 60 seconds! In 1985, Fred founded FMA, Inc. to design and produce R/C equipment for modellers and the military. The R/C equipment field included up to 15 US companies; FMA, Inc. was the last to produce US-made RC equipment.
Lithium Polymer (LiPo) Batteries offered one-seventh the weight and low self-discharge
compared to Ni Cds.
Lithium began to gain acceptance in the 1970s
Cost and volatility limited broad applicability until near 2000. Volatility yet today is still limiting, with stiff regulations for shipping. At FMA, Inc., applicability of, then more expensive Li Po batteries, to micro-RC models led to a business decision to transition from R/C radio equipment to Li Po batteries and strong marketing and promotion of the Li Po for electric power. R/C models could barely tolerate the weight of Ni Cd and Ni Mh packs. Said Fred; “My first experience comparing a Ni Mh was a demo to Frank Fanelli, Editor of Flying Models in 2002. We flew my electrified six-foot span Goldberg Sr Falcon using the latest Ni Mh pack. The Falcon still lives and flies! The flight was less than three minutes and the pack got so hot you could not touch it! Then I substituted a 3.3 AH 6S Li Po pack that weighed 1/7 as much. We landed after 10 minutes and the pack was barely warm.” The Li Po packs, and the marriage of brushless motors and ultra-low loss ICs for motor control created a rapid transition from engine power to electric. As a result; in 2004, Fred was awarded the annual Man of the Year Award from The Circle of Excellence issued by Fly R/C magazine for his contribution to the R/C Industry radio systems and
introduction of advanced Li Po power systems.
The biggest impediment to that progress was the volatility of Li. Consider this: solid rocket motors use finely ground aluminium as fuel. Li is even more volatile. The biggest and earliest accident occurred at an airport in Japan when a forklift penetrated a pallet of Li Po batteries; the resultant fire penetrated a couple of concrete floors! That made world news! According to Fred, attempts to work with the cell manufacturer and one of the foremost electronic manufacturers failed to produce a safe charger by 2004, so FMA, Inc conceptualized and developed what we called the by-pass charger that has become
known as a balancing charger. Each cell has a “tap” that is brought to a tap connector that mates with the charger. In simplified terms: As a given cell reaches the specified State of Charge (SOC) current bypasses that cell via a low impedance Unijunction transistor so no or limited current flows through the now-charged cell and this ripples through the pack until the last cell is fully charged. As our technology
evolved, many more features and info were introduced; e.g., cell internal resistance that warns when a cell is “going south”. www.fmadirect.com.
This evolution has continued at FMA to the point that our BUMP technology allows the user to touch the pack to the charger and have the optimum charge automatically set. Larger cell sizes and packs up to 12S are addressed by OEM/Military qualified chargers http://www.fmadirect.com/EngineeringForTheFuture.pdf
The “Leap” to commercial drones has taken 12 years in the US!
The basic technology for commercial drones evolved quickly from 2002 when FMA introduced and promoted the first Li Po packs. The FMA Co-Pilot infrared stabilization system was followed by the development of MEMs versions of the original Inertial Navigation System (INS) that first saw application in the AN/USD 5 drone Fred worked on at Fairchild. That initial system also was used in the Minuteman missile and the Apollo spacecraft. It weighed over 100 lbs and occupied over a cubic foot of space!
The infant drone industry grew out of the R/C hobby. Sadly, the first concerns about drones arose from indiscriminate operation by the usual few.
While other countries were vigorously pursuing the drone business, the FAA slowly came to life.
In late 2008, three FAA representatives visited FMA, Inc. for a day-long discussion of drones, or small unmanned aircraft systems s(UAS). The FAA ARC was instituted in late 2008 as ordered by
In Jan 2009, Fred Marks accepted an invitation to be a member of the Air Regulation Committee ( ARC) for sUAS along with Patrick Egan and 18 others. Fred was asked to chair the Command and Control (C2) aspect of the ARC. At the first meeting of the ARC, several areas of emphasis from C2 to licensing were identified and the 20 invited members were asked to sign on to one of the sub-committees.
Imagine Fred’s surprise when no one else joined C2! However, the non-technical (regulatory) groups each had several members. It then became necessary to recruit C2 team members from Government and Industry to formulate and input the guidance for C2. Fred says “I am most grateful to that team, Particularly Tom Alfieri of Honeywell.”
Almost all the technology and history for C2 (as opposed to sensing and data transmission) came from the R/C hobby and from Military R&D.
Batteries are the most important consideration.
The 70-year history of R/C to that time showed that battery failure constituted about 70% of all failures, whether in models or drones. Thus, the ARC as a whole, asked that batteries receive separate guidance within C2. The ARC also recommended that resulting regulations be embodied in a series of Standards for sUAS and that batteries have a special standard per https://www.astm.org/SNEWS/JA_2010/outreach_ja10.html The mechanism was for FAA to contract with the American Society for Standards and Materials (ASTM) to generate those standards.
Chairs of the ARC C2 Sub-Committees were not permitted to chair the standard sub-committees, thus Fred was recruited to chair the battery standard. Again, there were no volunteers so a group was recruited from industry and the military. The resulting standard was issued as ASTM F3005-14A; Standard Specification for Batteries for Use in Small Unmanned Aircraft Systems (sUAS) developed by Subcommittee F38.01.
You should acquire a copy as follows:
Batteries receive little “press” today, but losing a drone costing up to $250,000 to battery failure has a huge impact on the bottom line. This was the thrust of the ASTM battery standard.
Most of the press today is aimed at sensors, mapping, remote ID, and data transmission.
This is because the FAA and those who lobby are targeting the drone industry regarding safety or data retrieval. ASTM F3005-14a is accepted internationally and is intended to provide assurance to developers, users and investors alike that the batteries and battery maintenance system is no longer the “weakest link” in drone performance.
As the team wrote and reviewed F3005-14A, the following items are of paramount importance:
- The so-called C-rate. Fred accepts that he initiated that term (when FMA, Inc. first promoted Li
Po batteries) as a way of defining what discharge rate a cell could safely produce. Then the “C race” was on with each advertiser jacking up the number. To put it brutally: yes, many cells have been advertised as 10C; 20C and even up to 50C and greater. The missing link was how hot the cell would get at the declared C-rate. The other concern is usability at the C-rate. Consider that, e.g., a 3.7AH cell loses capacity at, say, 70C to 2AH. Then the discharge time would be 2AH/70A=1.7 Min; perhaps usable in sonar for a few bursts but not for much in a drone. F3005-14a places an upper limit on cell temperature ( characteristic thermal threshold; CTT) during discharge at the C-rate. Exceeding 140 Deg F (60 Deg C) shortens life cycle and can cause ignition.
- The Standard does not specify life-cycle; which is drastically affected by CTT. More than one pack purveyor has built a market by placing free packs in the hands of R/C competitors; but it quickly became known that those competitors were receiving new packs after just a few flights; i.e., the life cycle at the claimed C-rate was, at best, less than ten cycles – not economical when the user needs to fly a dozen or more flights on one drone job. If your cell/pack supplier will not show compliance with F3005-14A, would you risk your bottom line using that pack Most cell suppliers are reluctant to certify life cycle because it means a representative sample of each cell type must be tested down to an 80% DoD—a lot of testing.
- The other key standard is depth of discharge (DoD). This is the ratio of cell or pack capacity expended relative to its terminal capacity. The key element is: At what DoD is a cell declared to be at end-of-life? The norm has been 80% or 3.36V for a 4.2V Li Po cell. Though not established by F3005-14a; considerable effort has been made to relate cell Internal Resistance (IR) to that 80% figure. However, at this time IR must be considered by comparing IR level at a given cycle vs what it is at new condition. More importantly, if an uncharacteristic shift is seen in IR, then that cell is suspect. In earlier times, it was not uncommon to replace a bad cell. However, as packs have reached “commodity pricing”, it is not worthwhile. When one cell goes, can others be far behind?
- Standard F 3005-14A is the property of ASTM; thus we cannot reproduce specifics for the responsibilities laid on cell producers, pack assemblers and the end-user(s). Suffice it to say that purchasers of cells or assembled packs should require process control plans; quality assurance plans; the material data sheet (MSDS); technical data sheet(s) and that every cell should have on it the lot number and supplier’s name. These requirements should be made part of any RFQ the reader might issue. Rest assured, the supplier will not usually be happy to provide these data since drone builders do not usually purchase in 100K quantities or higher! Among key standards for the pack assembler is that cells must be graded, all cells in a pack must have been manufactured within a six-month period and all cells in a pack are tested for capacity and found to be within 5% of each other. Who knows; that might save an expensive drone!
- Section 8 covering charging and maintenance is the responsibility of the user. In particular, Section 8.1.1 sets the standard for charging and it is this area in which FMA, Inc has excelled for over 17 years including cell-balancing technology. Branded Revolectrix®, the latest PowerLab Touch Series II Battery Workstations now include BUMP Technology; a user experience so simple that all one has to do to safely and precisely charge any battery chemistry is BUMP the pack to the charger, CONNECT, and press GO. For information on the new Series II models, click here.
Drone designers, manufacturers, sellers and users are urged to review information at
www.fmadirect.com. Here you will see battery maintenance solutions that support up to 12S Lithium Chemistry Battery packs and High Power (1000W) Charge/Discharge. Click here to view a YouTube video demonstration of the new FMA Direct 12SOEM Battery Maintenance System presented by Tim Marks, President, FMA, Inc.
When visiting the FMA Direct website, should you need assistance with an ongoing project, please complete the form at the bottom of the homepage to describe your requirements. Someone will respond promptly and/or direct your inquiry to the appropriate technical personnel who will reply via email.