Progress update: I bent up the frame arms at work. Because the bends run in two directions I had to get up on a big table to do the second one. It turns out that if you bend a 10’ long section of tube 70 degrees it becomes very awkward to work with! The tubing connectors I ordered to connect the frame parts didn’t fit; the OD of the tubing was bigger than I expected. Luckily at 29.6mm the 30mm ID connectors from Kipp should fit great. I put in an order for those yesterday. I also ordered the batteries (6x HRB 6S 10,000mah)
Based on @bratwurst’s comment about motor heat I decided to downsize the prop to a 34x22 for the first round of testing. The predicted climb rate is ~374 fpm now, but the motor heat with “good” cooling in eCalc is down around 80C. I’m hoping the cooling is better than good, and I can move up to a 36x24 prop for a bit more efficiency. I have a RFQ in to Neumotor for the motor, controller, and prop adapter, so once that gets ordered I’ll have all all the expensive stuff on the way! I’m committed now!
I de-soldered the potentiometer from a servo tester and added a jumper wire so that a hall-effect thumb throttle from an electric bike/scooter can control it. It’s running ok on a single lipo cell, but that is outside the voltage range for both the servo tester and the hall effect chip. I had a little 3A BEC, but when I got it all wired up the BEC is bad and it’s not regulating voltage, so I’m waiting on a new BEC to finish up the wiring. I also need to remove the little pushbutton switch that changes modes on the servo tester. I do NOT want that thing getting bumped into ‘cycle’ mode when the motor is armed!
My plan is to power the BEC off the balance plug for the first battery in series on the right arm, and to mount the BEC and servo tester in a small project box with a power switch to the BEC so I can disable the throttle control when I am not using it. The thumb throttle will go on a scrap of bike handlebar with a bike grip below it, and a strap on the outside to secure it to my hand. I realize it’s not an ideal throttle setup, but I’ve seen others using something similar and it should be a workable solution to start with.
More progress: I taped the frame together and attached it to my harness to hang in a simulator to check the fit and clearance. I taped some weights on the front to get it to balance out. It looks like my bends worked out just right, as it looks very close to what I drew up in CAD. I think I can shorten the rear up a couple of inches, which should let me bring the batteries an inch or two closer to center as well.
The frame is attached to the carabiners using two 22" slings that I sewed up from 16mm tubular webbing. They are prussiked around the frame arms, and the tails are clipped into the carabiners.
The plan is to ground launch, since I want to use it to climb up into the lift band and then shut it off. It balances very well. I did some tests going from standing with the whole rig hanging off my shoulder straps, to lifting myself off the ground with the hoist, and then getting in the pod. It is not pitching more than 10 degrees, and with the prop spinning and providing some gyroscopic stabilization that should get a lot better.
please consider the extreme twist danger with lateral front stall and one-sided stall. you can sit up straight and bring your legs to the center as you learn in safety training. but the drive mass will maintain a moment that favors the twist. only meant well.
It’s a very good point. I’m going to do all the initial test flying with an upright seat harness to decomplicate things and reduce the chance of a riser twist. I don’t plan on flying this in really rowdy thermal conditions; it’s more for late afternoon ridge soaring and glass-off (restitution, I think they call it in Europe), and with a B wing.
Project update: I got my 90 degree couplings from Kipp. They are just slightly too big, but I’m able to shim the tubes with a couple of layers of 3.5 mil aluminum tape so everything is secure. All the couplings and tubes are going to get drilled and through-bolted as a backup, but I want the clamp joint nice and tight so there isn’t any free play. I cut the side arms down to size, and that leaves 3" of clearance between the back of my fairing and the motor support. I can probably trim a little more off, but since the consequences of having too much clearance are minimal and having too little are disastrous, I’m leaving it long for now. I stll need to trim the motor support down so it is flush with the couplings.
I’m starting to experiment with mounting all the small parts.I got two of the same switches used on the openPPG, one for each arm, so the whole system can be shut off with the batteries still connected. The switch for the left arm (pictured) just barely fits inside the project box it is mounted to. I did it that way so I can protect the studs on the switch from the metal frame. The switch on the right arm will be inside a slightly bigger project box, that will also contain the BEC and servo controller for the throttle system, as well as @GliderPilot’s pre-charge system. That side will have an additional switch to cut power to the BEC, so I can arm/disarm the throttle control.
I’ve ordered virtually everything that I need to complete the project, at a total cost of $2650. My motor, controller, batteries, and wiring should be here by the weekend so I can start getting things wired up. It looks like the last piece of the puzzle to arrive will be the prop; that should be another six weeks as it’s being custom milled by JC super props, and shipped to the US with a larger shipment going to Aircraft International.
This beast showed up today. It looks huge in the picture, but it is surprisingly small considering it’s rated for 22kW continuous. Same with the motor controller. I’m a little skeptical that those things are going to get me in the air, but even running them at half their rated performance should give me enough power. I guess I’ll find out when I get it all built and running!
Thanks! I read that when I was researching the motor. I doubt he was getting a lot of cooling air through the stator with the motor mounted transverse on an aluminum plate. I’m hoping I can do better with an in-line mount with holes to let airflow into the stator, and possibly some ducting to channel free airflow from the side of the harness into the stator vents.
At any rate, I’m planning to gradually ramp up the power and then the run times in ground testing so I can catch an overheating problem before something gets damaged. It also sounds like I need to research some kind of temp monitoring system that I can use in flight to keep tabs on the motor and controller while I’m in the air.
Quick update: I’m still just working on electrical odds and ends for the control system. I’m using some small project boxes to house the battery cut-off switches (one per battery bank, since they run in parallel).
The larger one also houses @GliderPilot’s precharge (anti-spark) circuit, and the throttle circuitry. The SAFE/ARM switch will cut power to the 5VDC power supply for the servo controller in the SAFE position, so if any part of the throttle system goes haywire (or just when I’m getting the thing strapped on, or for any other reason) I can totally disable the throttle while still having the motor controller powered up. I have a little more connecting/soldering/mounting to do before I can finish the big box up, but I’m waiting on some four-conductor wiring so I can send the throttle signal back to the ESC in the back and bring 7.4VDC power up from the right side battery bank to power the 5VDC power supply.
My battery packs showed up yesterday from HRB, and they look to be in good shape minus some slight creasing on one of the packs. All the cells in all six packs were 3.82 +/-.02VDC. What is unfortunate is that despite the listing on aliexpress specifying that the pack had 8AWG wiring, they came with 10AWG. Not really a show stopper, but I’m waiting to hear back from HRB on what they will do about it. They did wire up the packs with AS150 connectors with my specified polarity, which was nice. The packs are set up so that I can plug the positive plug from one pack into the negative plug on the next one, so I can get all three packs in series on each battery bank.
I finished up the hand throttle, control circuit, and enclosure. The thumb throttle setup isn’t ergonomically perfect, but it’s good enough to get me in the air. The servo is just there for testing. Not pictured is the adjustable, releasable strap that runs around the outside of the throttle grip.
More update: just plugging along on small stuff. I went back and forth about how I wanted to build the motor and motor controller mount, stressing out about cooling air, ect. In the end I decided to just throw something together using 3/4" ply, just so I can get components mounted to the frame and start the wiring process.
I started playing with the cage design as well. I’m using 8mm carbon tube for the hoop, and 8mm fiberglass tube for the spokes, with some T connectors from the kite world to join them together. I expected to use the fiberglass for the hoop and carbon for the spokes because I thought the fiberglass would be more flexible, but it was the other way around. The spokes will attach to the hexagonal motor mount.
I cut out the battery mounts from the same 3/4 ply as the motor mount. It seems like 50% of this project is: drill holes in something, then drive to the hardware store to find screws that will fit.
The initial motor mount is done. I’m not in love with the material; the plywood compresses a lot when tightening down the bolts for the motor. Despite that, it does feel totally solid once everything is tightened, and it should be good enough for at least some initial motor runs. In the long run, I’d like to have a similar shape cut from 1/4" aluminum, both for some additional heat sink surface for the motor, and for extra security.
The motor controller will be mounted as pictured, with the capacitor bank on the other side of the same fin. All of those tube clamps will be drilled and through-bolted as a backup once I have the motor position and thrust angle set
The cage is done. I had to make some slight adjustments to the segment lengths of the tubing to make it all work. My first attempt at making the ring resulted in a diameter that was a bit too big. Depending on how the performance is with the 34" prop I may make the cage a little narrower. It’s currently 42" wide to accommodate a 36" prop.
I temporarily mounted everything I have finished to the frame. It’s starting to look like something! Next up is to mount the motor, controller, and cap bank for real, and then finish the power wiring. After that, it’ll be ready for the initial power-up.
I’m also building a charging setup, using two DPS-1200FB power supplies running in series to supply a ISDT T8 charger with 24VDC. I should be able to parallel-charge three 6S 10aH batteries at 1C, so I can do a complete recharge in 2.5 hours. The DPS-1200FB power supplies are beasts… they are rated for 900W each, and are selling on ebay for $25 a piece. $50 and some tinker time will net you an 1800W 24VDC supply!
Quick disclaimer: if you wire these power supplies in series you need to do some modifications first to be able to do it safely (mainly: float the ground on the second power supply). Do your homework before you attempt this.
yes i confirm the server power supplies work very well. many in the professional competition use 3 D helicopters and 12 S power aerobatic aircraft. an important clue! if someone uses 2 in parallel. do not let the batteries run in parallel! otherwise there is a galvanic short circuit via the power supply that feeds the power supply. just as a hint.
I finished up the drive unit yesterday. The ESC is mounted above the motor, with the capacitor bank on the opposite side of the mounting fin. I found out that a friend has access to a plasma cutter that can cut 1/4" aluminum, so I’m hoping to replace this plywood motor/controller mount with an aluminum version at some point. Still, this setup should be good enough to get the motor spinning, check thrust angles, and do some testing. I’m mostly concerned with fasteners coming loose from the expansion and contraction of the wood with temperature and humidity. All the fasteners that run through the wood are either thread locked or are using nylock nuts. Coming from the bigger aviation world, I’d rather have safety wire and cotter pins, but that is hard to pull off with hardware this small.
I also had the chance to mount everything on the frame for the first time. The balance is almost spot on; the batteries may need to come back just a bit but I need to figure out the placement of the clip-in straps before I do that. Once I have the thrust angle dialed I can drill and pin all the tubing couplers to prevent rotation. The last thing left before I can spin up the motor is the power wiring! Most of the connectors are already soldered to the wire. I just need to cut everything to length and finish it up.
BTW, I got one of those Weller 200/260W soldering guns for doing the 8AWG wiring connections and it is absolutely the right tool for the job. It was well worth the money. All the AS150 connections are done with solder, and the ring terminals for the motor, ESC, and cap bank are crimped, soldered, and secured with screws, washers, and lock nuts.
One last thing I’m trying to figure out is how to balance the prop. Horizontally it is pretty close, but I had to add a lot of tape to the hub to get a good vertical balance. Compared to the overall weight of the prop it is pretty reasonable, but I’m a little bit at a loss on how to securely add that much weight to something spinning at 4000 RPM. The typical RC techniques of sanding and tape aren’t going to work. I’m going to experiment with adding washers under the prop bolts, but they are so close to the center that I’m skeptical it will work. Maybe I’ll have to use a micro-version of the “drill a hole and add a lead plug” technique used on larger propellers.
In rc I used to spray thin layers of transparent paint finisher on the lighter side. The advantage is that the prop shape does not really change, Wich could cause dynamic imbalance when the prop is sanded. Nice project!
I thought about doing that, but the lateral (tip-to-tip) balance, where they spraypaint trick works, is pretty good. The major imbalance is vertical, at the hub. I’m sure there is a way, I just need to do some experimenting. I suppose I could even sand a little material off the heavy side of the hub. Mostly I just don’t want to mess up the prop because it’s expensive, and it looks very nice!
I got my motor spinning for the first time today. I discovered that my throttle is working backwards, so when I let go it goes to full throttle, and when I press down it goes to zero! I was going to wire in a servo reverser into the circuit, but I decided to order a little $18 programmable servo controller board so I can make it work exactly how I want. That is probably what I should have done in the first place, instead of my hacked-together servo tester setup. Plus this will finally give me an excuse to learn how to do some simple programming. It was still nice to see the motor spin!
My other setback was that when I tried to turn the power off my cool @GliderPilot precharge switch broke off! Paul, any ideas? This was printed for me for free by a friend, and it looks like the bond between layers is super weak. Maybe an SLS print from shapeways would be stronger? What is odd is that I have turned this switch on and off a whole bunch of times, but the first time I had power running through the switch this happened. Seems like a strange coincidence.
