RCU Review: Greg Covey's Amp'd Issue 2: Arming the Big Boys

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    Contributed by: Greg Covey | Published: November 2007 | Views: 52241 | email icon Email this Article | PDFpdf icon


    Issue 2
    Article By Greg Covey


    When it comes to making electric conversions easier, I am always eager to use new products in my next project. This month's column shows a few of these items that have helped make it easier for me to fly electric and "arm the big boys".

    On some plane designs, it is particularly difficult to access the battery packs without making extensive modifications. This scenario is often seen on scale warbirds where you don't want to detract from the look of the plane or weaken the fuselage by cutting the frame for a hatch. On smaller electrics, connecting the battery to arm the plane before flight is acceptable. When you start getting into larger electrics and glow conversions, it is often difficult to gain access to the battery connections for arming the plane. Further, it is just plain dangerous to leave it armed even though the Electronic Speed Control (ESC) keeps the motor off when there is a Loss-Of-Signal (LOS) from the transmitter.

    For many years, the only convenient arming system that I used on electric conversions was developed by Tom Cimato of MaxCim Motors. Adding a MaxCim Charging Harness allowed me to safely arm the plane at the flight line as well as re-charge the batteries while keeping the wing on. I found these features to be invaluable for full day events. You can set up your planes in the morning and keep flying or recharging all day. You simply taxi into the pits and plug in your charger after a cooling period.

    The MaxCim Charging Harness on the right was modified to use Dean's Ultra connectors, a 40-amp ATO-style fuse, and a single battery connection. My hope was that someday this type of charging harness would be sold to R/Cers for easy recharging of the battery packs in the plane.

    The ATO fuse moves from the 'Operate' to the 'Charge' position to connect the charge jack and disconnect the battery from the controller. This assembly allowed me to mount my Hangar 9 Corsair F4U wing once in the morning of an R/C event and simply taxi into the pits for a recharge. At the time, it was a true convenience for arming the system and charging NiCd or NiMH packs.

    MPI 6790 Arming Switch

    MPI 6790 Arming Switch

    Maxx Products International (MPI) has a new part called the 6970 Arming Switch. In addition to adding safety to your power system by keeping the motor disarmed until you reach the flight line, the Arming Switch allows you to easily disconnect the ESC (by unplugging it outside the fuselage) to recharge batteries in the plane. The assumptions here are when using LiPo packs, you have access to the node connector and use a balancer or balancing charger for safety.

    When using two packs in series, you can also use the 6970 Arming Switch to disconnect the two packs so that they can be charged at the same time (by separate chargers) without having a ground fault issue. Simply install the 6970 receptacle into the fuselage side and connect it in-between the battery and ESC. No soldering needed!

    The MPI Arming Switch mounted easily in the soft thick balsa area of the P-51D fuselage.

    The wiring harness for my Hangar 9 P-51D conversion is greatly simplified by the new 6970 Arming Switch from MPI. It can be mounted right in the fuselage and will either arm or disable my entire power system with a single plug. Since the black plastic housing pulls apart to expose the receptacle, the 6970 Arming Switch can be mounted from either the inside or outside of the fuselage. By having access to the balance (or node) connectors, I can recharge both packs right in the plane without removing the wing. I don't even need an additional On/Off switch to the receiver. The Sermos (a.k.a. PowerPole) connectors on the 6970 Arming Switch can handle about 50amps continuous current and about 100amps peak current for short bursts. This capability makes it a good solution for most electric conversion applications.

    I re-wired my MPI Arming Switch to eliminate a pair of Dean's Ultra connectors. Since I was using two 5-cell Lithium packs in series to obtain a 10-cell total Lithium voltage, I also needed an On/Off switch in-line with the UBEC power inputs.

    Note: A future column will discuss series and parallel packs.

    photos by "Papa Jeff" Ring

    The MPI 6970 Arming Switch is much less noticeable than the MaxCim Charging Harness so it is a favorable choice on scale models like the Hangar 9 P-51D and Corsair F4U. The evolution of the arming switch (and arming higher voltage ESCs) still has a way to go but we are now seeing new products on the market that address these issues.

    Battery Disconnect Switches

    When I cannot find a product I need for electric flight, or the product is more expensive than expected, I often go outside the R/C industry to look for what I need to get the job done. This situation arose when I needed to enable a 200amp power system for my 1/3 scale Clipped Wing Cub. I had a motor and controller that can draw up to 200 amps but no product to help me properly arm the system. I discovered that Battery Disconnect Switches were a common product in motorcycle racing, RVs, and campers.


    The 100amp to 500amp "Little Switch" from Flaming River Industries (shown above) is available in a simple switch-only form for $20 or with mounting plate, hardware, and rubber seals for $28. I purchased mine from a known good source like Summit Racing Equipment.

    For my application, the mounting plate was not needed as the switch was mounted to the fuselage wall of a third scale Cub. The rubber cover is really meant to keep the switch clean in racing environments where oil, fuel, or dirt can more easily come in contact with the switch. To keep the switch from protruding too far, I made a thick washer from the foam flooring I used to line my trailer floor. These flooring pieces can be purchased at most home improvement stores and cut easily with a razor knife.

    The procedure to arm my third scale Cub power system (on the right) is to first throw the anti-spark toggle switch and a few seconds later insert the removable key and turn it to arm the system. This also locks the key in place for the flight.

    A combination of the anti-spark switch on the Jeti SPIN200 ESC and the Battery Disconnect Switch make this 6000 watt, 200amp power system easy and safe to enable at the flight line.

    Best of all, the 14s power system is armed spark-free!

    Spark-free Arming a 1/3 scale Cub

    This U.S. General Battery Cut-off Switch from Harbor Freight is only $6. It can handle 100amps continuous @ 12 volts or 1000amp surge for 10 seconds and comes with two keys.

    Powerwerx Powerpoles

    For someone looking to make their own arming device, Powerwerx sells sets of Powerpole connectors that vary in current handling capability from 15amps up to 350amps. Chassis mount housings are also available in multiple sets of connectors that could be mounted inside or through a fuselage wall.

    "Jones Witch"

    The "Jones Witch" from VampowerPro.com is a switch mechanism that enables the battery in an airplane by inserting a plunger when you are ready to fly. It has a positive locking mechanism that offers a bit of resistance when the plunger is pulled so it doesn't accidentally shut off.

    Only the small plunger head shows outside the model and these devices are rated to handle over 100 amps with bursts to 180 amps for 30 seconds.


    When using larger electric or glow conversion models, the easier you can arm and disarm the power system, the safer you make it. Never completely rely on the ESC to keep the motor off when the power system is armed and always alert people around you when they approach an armed prop. Unlike a gas or glow-powered plane, a stopped but armed electric prop is a tremendous safety hazard! A faulty ESC, receiver glitch, or bumping the left stick are all possibilities for an accident. When you fly electric, fly clean, fly quiet, and fly safe!

    This section of AMP'D covers some of the questions that our readers have sent in and I thought would be interesting for others.

    Jeff asks: "My ESC doesn't have an anti-spark feature. How can I get my battery connection to stop sparking when I first plug it into the ESC?"

    Greg: Many of my ESCs also sparked when I connect more than a 5s LiPo supply to them. The Jeti SPIN200 ESC that I am using was the first one I had seen with a built-in anti-spark feature. Is is fairly simple to make your own anti-spark feature by using a 50-100ohm 1/2w-1w resistor. Shown above are three size resistors compared to a penny. These parts can be purchased at your local Radio Shack.

    The resistor can be wired in series, as shown above, to the plus side of the battery to ESC connection. This can be done with a second parallel set of connectors or a switch. Simply plug in the anti-spark connector first and then the normal battery connection to the ESC, about a second later. You can use thinner wires for the anti-spark connection like those commonly seen on Lithium battery balance plugs.

    Frank asks: "I plan on using two AXI 4120/18s, APC 13x8 electric props and two Jeti 77-Amp ESCs in a Top Flite Cessna 310. I was wondering if it is okay to use one battery pack (actually 2 Flightpower 3700mah 6-cell packs in parallel)? The batteries would be installed in the fuselage. Is it better to install each pack in the nacelle, one for each ESC?"

    Greg: Jeti recommends using a separate pack for each motor/ESC combination. The reason is to eliminate the motor noise of the second motor so that the ESC can properly detect the position of the magnets on the outrunner case. On my dual AXI 5330 setup and my twin AXI 4120 powered P-82 Twin Mustang, I used separate packs. That being said, on smaller models like the new E-flite P-38 Lightning 400 ARF, it uses a single LiPo pack for both ESCs. I have not seen a problem with the power system on this model.

    Where the packs get installed doesn't really matter. As long as the noisy Motor to ESC wires are short, the battery lines to the ESC can be long.

    Ask questions by e-mailing me at greg@rcuniverse.com

    This section of AMP'D reveals some of the feedback or suggestions that our readers have sent in about previous issues.


    Tom writes: What I consider a "ParkFlyer" is generally anything less than two pounds that is hand launched, or ROG's (rises off ground) with landing gear. What I consider to be the limitations for a Parkflyer, have not so much to do with the size of the plane (or Jet) but how that plane is flown in the "Park" like setting.

    This whole topic of what is a parkflyer boils down to what you can sensibly and safely fly in a particular area, given the amount of space, and who is there with you. My website has a page called Sensible Flying Tips that covers this topic in more detail.

    You should point out that the flyer must also determine if it is Legal to fly in their area, if it's public, or have the owner's permission if they are flying on private ground. Somebody owns or has rights to everything, and that perfect flying field you found may have an irate owner attached to it. Flyers need to check with the Parks Department or local Police before flying anything. (One good way to convince someone to let you fly is to show them your AMA Card, and explain the Insurance coverage you have.)

    If people want to establish "What is a ParkFlyer" they should look at setting up a reasonable Maximum Limit to Overall Size, "Watts per Pound" and Aircraft Speed, and let everyone design Parkflyers and ParkJets around those parameters.

    Once you have that established, then you can look at a minimum "Flying Space" requirement. Anything within the Maximum Limit can be flown as a ParkFlyer, and anything over the limit should be restricted to an AMA approved flying field..(Regardless of what powers it, or how it's built, Except for Powerless Gliders).

    You have a great start to your column, best of luck!!!

    Tom B.
    RCParkflyer @ RCGroups & RCUniverse
    Parkjetsflyer @ Wattflyer

    Tim writes: You address a topic which many marketing folks would rather not discuss. I appreciate your candor. No one in our hobby, young and old alike should be fooled by the 'Parkflyer' bullet on the box of so many models these days. Whenever anyone puts anything in the air with a spinning prop, regardless of power system/ energy output, we must have an inherent mind for the safety of others who may be around. Your points really hit home here in California at our crowded Electrics only RC field that we share with many hikers, bikers and future R/C'rs.


    Tim Stahlke

    Make suggestions by e-mailing me at greg@rcuniverse.com


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    Comments on RCU Review: Greg Covey's Amp'd Issue 2: Arming the Big Boys

    Posted by: trebel on 06/16/2008
    Great article. I would like to copy but can't get it to print. Help please. Dick Trebel trebell@cox.net
    Page: 1

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