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May 24, 2017, 10:05 PM
"I will return" Federico
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Build Log

The Bee's Knees in Battery Breeze?

Last November I purchased an 87" 3DHS Extra 300 SHP, my first giant scale plane, with the goal of using it to compete in IMAC contests this year. It will be powered by an Xpwr 60cc motor and two 6s 6000mAh 35C Glacier batteries.

Never content to build an ARF, or kit, without customizing it to make field setup or flying easier, I went about drawing plans for modifying the Extra. Among the many items on my to-do list was a battery tray that would simplify the steps needed to insert and connect battery packs to the ESC. The plan was to make this a winter project that would be ready for spring flying, practice and the first IMAC contest in the North Central region in May of this year, 2017. Plenty of time, right? Well, events never seem to go the way you plan.

I do CAD work for a living (AutoCAD for civil engineering), so drafting plans for the custom parts I needed was not a problem. But creating a prototype of something that has never been done before requires a considerable amount of time designing, testing, building, testing and re-designing until you have something that comes close to your original concept. With two kids, a house and a full-time job to manage, I have relatively little time to work on my RC hobby. Apparently, I spent hours of that precious time just staring at my plane as I mulled over the next step in the process. Creative products take time!

In the beginning of this project the idea struck me that a battery tray could do more than just hold a battery; it could also make the connections to the ESC for you automatically. I hate fussing with wires and velcro in cramped spaces, especially after unknowingly disconnecting a battery lead to the ESC in my little 55" Extra prior to an IMAC flight last year. With the judges watching, and waiting, I flipped the throttle safety switch off on my FrSky transmitter and moved the throttle all the way up to arm the ESC, and ... nothing happened! I had to scramble to remove the hatch, diagnose and fix the problem, replace the hatch and takeoff in the span of two minutes or get a zero for that flight. Talk about pressure! I was too rattled to fly a good sequence (actually two, back to back) and resolved to never let that happen again.

Ask yourself this question: do the designers of gas powered planes expect you to disconnect, remove and reconnect fuel lines every time you refuel the plane? You just open the fuel dot and overflow line and pump your fuel. Why should electric powered planes be any different? Eventually we'll be able to do the same; just pump in more electrons and resume flying. Meanwhile, it seems the least manufacturers could do is provide quick connect parts to make insertion and removal of the battery (or batteries) a lot easier. The batteries should be a plug-n-play system, with connection to the ESC automatic during insertion.

I searched the internet for a battery tray that had a quick connect system similar to what I had in mind. Yes, it had been done! But only for one specific helicopter (Goblin 380), and too small (in battery capacity and amperage) to use any of the parts for my purpose. The animated video alone is well worth the click. Here is the link to that system: Goblin 380 Quick Connect Tray

As of today I have completed most of the testing required and built three prototype battery trays. Smith Precision Aircraft did all of the laser cutting from AutoCAD plans I drafted. Jason Smith did a super job and provided a quick turn around on all of my orders. Thank you, Jason! I'm posting a few pics to get started; more to follow. I have yet to perform the final test with batteries in the tray. I was hoping to complete that before posting this build log, but I am so far behind schedule I decided to go ahead and get started here with a report of progress to date.

I hope you find this interesting and can learn from my mistakes. If you follow along, you will be among the first to see the maiden of an RC plane with a quick connect battery tray. Of course, if you know someone who has done this already, let me know. Eventually, I hope manufacturers will begin making connectors specifically designed for a quick connect system and make a lot of the work I had to do unnecessary for the rest of the RC community. Please take the poll I posted to let them know your view on a plug 'n play system for planes smaller than giant scale: RCgroups poll See Flying Giants for a similar poll for giant scale planes.

Comments are welcome.
Last edited by rclad; Jan 02, 2018 at 02:45 PM. Reason: Fixed typo.
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May 24, 2017, 10:37 PM
"I will return" Federico
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Design Goals

Design goals for my battery tray:

- hold two 6s 6000 mAh batteries weighing a total of 3.5 lbs

- fit inside a large Lipo bag with batteries installed

- reduce workload to replace batteries and get plane ready for flight or storage

- allow automatic connection to ESC when tray is inserted into plane

- allow automatic connection to balance leads for cell voltage telemetry

- reduce length of wire between battery and ESC (and reduce ripple currents)

- protect batteries and wire leads in flight and handling

- enable separate connection to each battery for charging without removal from tray

- create lightest tray possible that can withstand at least 10 Gs in flight, and hard landings

Results so far:

- tray weighs 3.5 oz and can easily hold a 40 lb load (over 10 G's for a 3.5 lb battery)

- tray fits easily in a large Lipo bag

- ESC connector assembly allows perfect mating of tray to ESC connectors every time tray is inserted into plane

The EC5 connectors that come with the Glacier 6s batteries can't handle more than 130 amps, so I am replacing them with XT150s rated at 150 amps. The tray has been designed for those connectors.

I realized early in the design process that the EC5 and XT150 connectors would require a considerable amount of force to plug in, especially when plugging in two pairs (4 connectors) at once in addition to two 6s balance plugs. After inserting the tray into the air frame I will need a tool to provide some leverage to complete the connection. See attached pic of an early version of that tool. The final version will have a long dowel (handle) attached to the top of the lever and perpendicular to it in place of the short wood dowel that is shown. That will provide a better grip for both pulling (to insert the tray) and pushing (to release the tray), since the tool must be inserted through the deck inside the motor box, and there is not much room left for big hands like mine.
Last edited by rclad; May 26, 2017 at 01:30 PM.
May 24, 2017, 11:44 PM
"I will return" Federico
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Plane Modifications

One of the more difficult decisions early in the project was the one to cut out the existing deck for battery/fuel. The deck looked well engineered and very light - almost too flimsy to support 3.5 lbs worth of batteries, but obviously it did its job over nearly a decade of service. But it had to go, because the new tray has the battery hanging below the deck where the exhaust canister would go for a gas set up. Not knowing if my design would work at this point, or how the shift in weight would affect flight performance made this decision even more difficult.

Before cutting I added triangular stock to support the deck remnants on either side of the cutout. These would have to support the aft end of the tray. I made a mock up of this to test how much weight the remaining deck would support, and it held up fine.

I added a 3 mm x 2 cm strip of aircraft grade (5-ply) plywood to the top of the deck and 1 mm ply underneath in front of the cut out to support the forward end of the tray.

Next was the addition of supports to the interior fuse to pin the tray in place. I spent a lot of time working on this design, and it changed many times, from an automatic locking mechanism using plywood plates and magnets to the current design, which is a manual system using 3.5 mm dia. carbon fiber pins that remain in place when the tray is unpinned. The pins not only lock the tray in place, but they also lock the two interior fuse sides together, replacing the connection that was in place with the original deck.

Just to be safe I will give this fuse, with batteries and tray locked in place, a good shaking upside down before that first flight. Its hard to anticipate what a bumpy flight (on a windy day) combined with aerobatics will do to a new design. Since I have used a similar design to hold my canopy in place on my little Extra, and have gotten over one hundred aerobatic flights on that with no issues, I am confident the pins will hold up to any abuse I throw at it.
Last edited by rclad; Jun 01, 2017 at 12:24 AM.
May 24, 2017, 11:50 PM
"I will return" Federico
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Tray Testing

I have a bunch of photos of the testing I did to make sure this tray will withstand the G forces in aerobatic flight. I'll post those soon.

Last night I did the first test of the completed tray with a set of batteries installed and all wiring complete on the ESC side. Initial plan was to glue the XT150 connectors in their housings with hysol, but at this stage I didn't want to take that step, which would have been hard to reverse if mating issues remained. So, I added a silicone non-slip pad to each of the connectors to provide enough friction to hold them in place for the test. (See here: DreamworksRC Silicone-Selfadhesive-Antivibration-Antislip-Pads ) I think my mistake was doing that and bolting the connectors in place without mating them first, so that they would be clamped in place in perfect alignment.

End result? A disappointing failure! Arghh! As I manually (without the leverage tool) inserted the tray to close the connection I could watch the alignment and verify the connectors were mating properly. Everything looked good. So I pushed harder, and harder. I knew it would take some force, so I expected to have to push hard. But it didn't feel quite right, so I stopped and pulled the tray back. One of the connectors on the ESC side had jammed against the edge of the housing on the battery side. It happened on the bottom side, so I couldn't see it. See pics.

I thought at first this might spell the end of any quick connect system using the flimsy XT150 housing. They really aren't designed for this purpose. But, I think I have a work-around solution that may save the day. I will post new results after I test it out.
Last edited by rclad; May 26, 2017 at 01:18 PM.
May 27, 2017, 12:18 PM
"I will return" Federico
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Poll on Plug 'n Play Battery Tray

Please take the poll I posted here for planes smaller than giant scale.

See Flying Giants for a similar poll for large scale planes (80" wingspan or greater).

If there is enough interest in a plug 'n play system for batteries in electric planes, manufacturers and vendors may start supplying the parts we need to make it happen.
Last edited by rclad; May 27, 2017 at 01:03 PM.
May 29, 2017, 12:33 AM
"I will return" Federico
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Final Test a Success

The connectors need to be held securely in place to enable repeated insertions and removal of the tray. Initially I thought clamping pressure alone would be enough, then decided on glue. I bought some hysol and a glue gun and set them aside for final assembly.

After repeated testing, some failures and much assembling and disassembling, I just couldn't make that permanent leap to glue. If a connector gets damaged or pitted beyond repair, it would be much easier to replace the part if it's not glued in place. Plus, it would be very easy to glue it in slightly out of alignment, and then it would be impossible to adjust.

With that in mind I finally decided on set screws to pin the connectors in place. They work great so far, allowing the tray to be fully inserted and removed repeatedly without any misalignment. Hopefully this method will hold up over the long haul.
May 30, 2017, 08:39 AM
"I will return" Federico
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Leverage Tool Makes it Happen

Up to this point I've been manually inserting the tray with the plane upside down so I could access and watch the process. Using my hands only I could just manage to force the tray all the way into the ESC assembly and close the connection. Getting the two apart was much harder. I was resorting to pieces of scrap ply to force the two apart.

Last night I temporarily set up the pivot blocks so I could test the leverage tool I made (seems like months ago, now.) It worked! It makes inserting and removing the tray a breeze. Yeah! I'll post a video soon, so you can see the process in action.

Once the pivot blocks are glued in place this project will be done. Oops, not quite! I still have two more trays to build, and they have to be exactly the same as the prototype in order to work. After that I can finally complete the installation of all the radio gear and get this bird in the air!
Last edited by rclad; May 30, 2017 at 09:29 AM.
May 31, 2017, 09:39 AM
"I will return" Federico
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Success doesn't come without some setbacks along the way, and this project has seen its fair share of those.

I was hoping to make a video last night of the insertion and removal of the tray in my Extra, but I wasn't quite happy with the alignment. It was taking more than a nudge to get the XT150 connectors to slide into each other, indicating a slight misalignment. As I inspected the tray I realized the issue was the plywood backing plate (part F1A - the part with four bolts in an early prototype, but only two in the current version). The plate holding the connectors in place was bending under the pressure from the bolts and pressing down on the forward part of the connector housing, bending it out of vertical alignment. (Sorry I didn't get a photo! I'll post some tonight.)

I initially planned on using 5-ply aircraft grade plywood to handle the load better. I had to switch to 3-ply in order to get the parts cut by laser. That worked out OK for the rest of the tray, keeping it light weight. This part is simple enough to cut myself, so I should have done that from the start. Ideally, if money was no issue, this part should be machined from 6061 aluminum alloy. Then bending would not be an issue, and it would remain fairly light. Looks like I will also need to add some support under the plywood plate to keep it from bending.

Once I replace the part with the 5-ply and add the supports I will try again and post a video.
Last edited by rclad; May 31, 2017 at 09:46 AM.
May 31, 2017, 06:57 PM
"I will return" Federico
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Load Testing

Here are some pics of an early prototype being subjected to load testing. I mounted a large hook to a block of wood simulating the batteries, then added various weights to the hook. Final test was a dynamic one: dropping forty pounds on the the hook to simulate a hard landing. The tray held up fine and showed no signs of bending.
Last edited by rclad; Jun 01, 2017 at 12:12 AM.
Jun 01, 2017, 12:36 AM
"I will return" Federico
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Tray Upgrade with CF

To reduce the bending to plate F1A when bolted in place I replaced it with 5-ply aircraft grade plywood. I had this piece in my shop for probably twenty years, so not sure if it aged poorly or got soft from moisture in the basement, but it really wasn't any stiffer than the 3-ply lengthwise. It seemed less prone to twisting, though, which was as much a problem when installed in the tray as bending. To reduce the bending I added a strip of 0.5 mm carbon fiber. Wow! What a difference. The plate is much stiffer now.

After installing the new plate I tested the tray. It connects into the ESC assembly much smoother now. Check out the video in the next post.
Jun 01, 2017, 12:57 AM
"I will return" Federico
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Proof is in the Picture, er... Video

I finally got everything completed for a demonstration video. Now you can watch the insertion and removal of the tray. Sorry I don't have a proper camera stand, so the angle is a bit off. I got this in one take, and since it's so late and I've got work tomorrow, I decided it's good enough for now.

Oops, can't upload. Here's a link: Battery Tray Demonstration Video

Is this the "bee's knees" in battery tray technology? Not by a long shot, but it works, and IMHO a step in the right direction. Hopefully, if enough people make noise, manufacturers and vendors will supply us with the parts needed to make a proper plug 'n play system.
Last edited by rclad; Jun 01, 2017 at 09:46 AM.
Jun 01, 2017, 10:47 AM
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Looks Great Greg, very well thought out design and the video proves it. Thanks for letting me be part of the project! I enjoyed it!
Jun 01, 2017, 11:06 AM
"I will return" Federico
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Thanks, Jason. I had B&E Graphix make a couple decals from your SPA logo, so I'll put those on my plane.

I can't wait to do the maiden. Only three weeks to my first IMAC contest this year with the new plane! I'm cutting this way too close!
Jun 01, 2017, 11:36 AM
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Thanks Greg, I appreciate the logo on the plane! I am also looking forward to hearing the flight reports. Good luck at the IMAC this year!
Jun 03, 2017, 10:09 AM
"I will return" Federico
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Please see my build log for the 87" 3DHS Extra 300 SHP for performance of the tray in the plane.
Last edited by rclad; Feb 28, 2019 at 01:57 PM. Reason: Added link to build log.

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