Thanks for this detailed post. Apparently, I didn’t read it thoroughly the first time. The good news is we independently concluded the MN601-S KV170 is a good choice for VTOL engines. Thanks for the steer to the integrated kit. Seems like a great solution. Perhaps I missed it in a subsequent post, why did you go with the individual components? Seems like the integrated kit would solve your mounting problems.
I am a bit concerned about your 1.5kg senor hanging 5 m below the airplane - that’s a long moment arm. Structurally, it’s going to add significant stress to the airplane, especially when swinging. Additionally, I don’t know how the flight controller will respond to the motion of the sensor. A quad has 4 engines that can quickly respond to counter the motion of the sensor. In plane, the control surfaces are all you have to counter sensor motion. I don’t know if you’ll have sufficient control authority (aileron deflection) to counter the motion of the sensor. The final concern is resonance. I wonder if it’s possible to get into a dynamically unstable situation, where oscillations grow instead of dampen, like the famous Tacoma Narrows Bridge.
I agree. The HK “jiao shui” glue was not as thin as the glue used in the MFE videos. I ended up ditching the brushes and just used it direct from the tube. Even then, it was fast to set.
Both the plane and the dogs are looking good!
Dave,
The Fighter 4+1 PIDs in the param file below should be good enough to start with. At least they seemed ok on my short test before winter arrived. If you have an issue, I can help with suggestions on what to tweak.
Hey David, we ordered the electronic package from MFE, and I can attest that their products look quality…note, we have not fired them up yet. The ESCs are branded tmotor, and the motors come in similar tmotor packaging, so I would not be supprised if they were made by tmotor as well…we went this route as I could purchase then using PayPal unlike Christian, and I figured why not use the electronics designed specifically for this aircraft…
Thank you for the information. Glad they appear to be quality. I’ve had good luck with T-Motor engines on my quads and trust the brand. My preference is to use MKE recommended parts but was hesitant due to unknown quality.
Thanks for the timely post as I was about to order the integrated MN601s combo Christian_H linked above, for a whopping $1,000.
How long did it take to get the electronics from MKE?
Do you plan to use the 2013 recommendation for the drive prop? I might go smaller to increase my efficiency.
Welcome back! I find a crashing drone a more “fun” way of losing money than stocks (probably cheaper too ).
*I drafted a response last night but then got pulled away before finishing it:
The MN601-S 170kV motor was my leading option until a TMotor rep persuaded me to go with the V505 kV260. The main reason I went with V505 is to minimize air drag during forward flight with a smaller prop (16x5.4 vs. 20x6). There is the potential for cost and weight savings depending on the motor mount. TMotor offered to custom make a V505 integrated kit for me but the lead time did not work. The MN601 is slightly more efficient than the V505 and since you have a lower MTOW than I do (11.5kg), I think it is a good choice. Unfortunately, the MFE stock motor mounts will not fit the MN601-S (68.8mm diameter) as the MFE mount can only accommodate up to 60mm diameter motor. They will also not fit the TMotor FLAME or ALPHA 60A HV ESCs. If you go 3rd party route for motors, I would seriously consider the 601-X integrated kits since they include a motor mount/housing and all you have to do is put it on the carbon fiber tube.
As Ian @FIT-RS mentioned, I am unable to use PayPal for this project so I was forced to look at 3rd party options. Reliable components are a high priority since my sensor payload is not cheap. TMotor has a good reputation for parts as you know and my budget was able to accommodate (fortunately). It appears that the MFE motors could be quality parts and it’s possible that they come from the same factory making TMotor.
A simple quality test could be done with a 3 channel oscilloscope and a hand drill/drillpress to look at outputs of voltage amplitude and phase shift of the motor coils. A multimeter could be used in a pinch but you won’t get phase information, however, quality/condition of motors tend to be more obvious in the differences of voltage amplitudes (all other factors the same).
For VTOL and hovering I will be using V505-260kV, FLAME 60A HV ESC with a TMotor P17x5.8. For cruise I will be using an AT4130 kV230, AT 115A ESC with an APC 17x10WE prop. All propulsion parts are TMotor and the ESCs chosen are the recommendations from the TMotor rep.
Over the years of drone building/flying I’ve watched too many crash. The last one was particularly painful. I’d rater lose $1,000 trading than witness that again! Hopefully, it doesn’t come to two lousy choices.
I am looking at the AT4125 with at 15x10 prop. My goal is to maximize flight time while maintaining sufficient t/w. Finding the right combination has been challenging. I plan to cruise within the recommended speed range (17 - 20 m/s). I think I can achieve that with the proposed set up at around 48% throttle, which is about 2200 g of thrust at 7.5 amps. It all looks pretty good on paper.
Since time is more important than money, I will like go with the 601 x. Great find. Thank you!
The sensor manufacturer strongly recommended a fixedwing over a multicopter since you wouldn’t have swinging motions when flying a grid mission due to stop-and-go at end points. Having forward flight helps to stabilize the load due to air drag being predominantly from one direction/vector. To avoid swinging and smooth data collection you’d need broad sweeping turns which isn’t near efficient on a multirotor. I should add that the recommended ground speed for the sensor is 19-20 m/s.
Ah yes, the classic example of resonant frequency. My physics teacher at Uni liked to show us the videos in lecture.
I agree with the concern of the resonance from the cable. I think that is the biggest unknown aside from air drag of the sling load and additional stress on the frame. The cabling has a braided wire loom sheathing that fits tightly and is slightly flexible though far from a wet noodle noodle. There is a separate, braided poly chord attached to the sensor housing with an anchor on the opposite end that is meant to take stress off the cable connections.
The bulk of the weight of the sling is in the cabling and not the sensor at the end point. Implication being that the weight is more distributed which might be undesirable w.r.t. resonance vs. having center of mass near the end of the sling.
I can empathize with your crash PTSD. I see building drones as far less of a gamble in the end though a lot more time and effort committed/lost.
For cruise or forward flight (FF), the AT4120 was where I started initially, checked out the AT4125, and then settled on the AT4135 since it gives me more thrust to deal with sling load drag and my build’s high MTOW. I can always drop down to a smaller motor to save weight and gain efficiency since I’m still testing the waters with this build.
The AT4125 has much lower internal resistance and a higher thrust range than the stock MFE motor, however, it is 130g heavier. From what I’ve come across in the various VTOL design rabbit holes, a thrust-to-weight ratio between 1.5:1 and 2:1 for VTOL mode is ideal. Cruise is a little harder to calculate because of wing and body lift. You need to have lift and drag coefficients which are not provided by MFE. The best we can do without flight test numbers is match stock spec’s or go slightly better. Stock MFE FF motor is in the ballpark of 4.8-5.0 kg of thrust so I think you could safely use either the AT4120 or the AT4125.
As a disclaimer, I am intentionally overbuilding my propulsion systems so I have room to play while testing and then I can step it down later if needs be.
@FIT-RS pointed out the TMotor integrated kits to me at the start of the design so I’ll give credit to him.
I plan to be doing test flights by the end of next week (weather pending) and then start collecting survey data ASAP.
My MaxxHaul Cargo Carrier arrived and it was a perfect fit for my MFE Fighter box, even with the cart wheels. Just strap it down with a few bungy cords and it’s ready to go! The aluminum frame is quite light and it also comes with a 2" receiver bar assembly (shown in last photo).
Normally, the cart fits right in the back of my Ford Expedition. The cargo carrier will allow me to bring more planes to the field or even use my smaller Ford Edge since both have 2" hitches built into the frame.
Nice. I still need to find a more permanent solution for a field case that is impact and weather resistant. I was debating getting a large camping/river cooler, gutting it, and putting most of the original shipping foam inside.
That could be a good short term solution and it’s affordable.
I got price quotes a couple months ago on a shipping case thinking it would be less than a pelican (or similar) case. Boy was I wrong. I should know better by now that if you have to ask for a price it’s probably not cheap!
I’ve got all the critical components set in place temporarily (some taped) so basically all that is missing from the final build is a bit of wiring and the Rx antennas. I wanted to do a CG test so I could see the approximate position of where the VTOL batteries needed to go and what sort of bracket/tray I should create to hold them.
As it sits, the VTOL batteries are 2 x 5000 mAh 6S 25-50C LiPo’s. These seemed to be the best bang for the buck w.r.t. energy density while having a high enough discharge rate to handle the V505 motors in a range of throttle values and hover times. After flight tests I will know if I can step down to a lighter battery of lower capacity and higher C rating. The cruise and system batteries are 2 x 12500 mAh 6S 3C Li-ion’s.
I eventually decided to go with a dual battery system primarily as a safety precaution for a few of reasons:
With a separate VTOL battery the pilot is able to know more accurately how much energy/time I have left dedicated to VTOL motors without having to guess.
The pilot can more easily achieve a maximum cruise flight time and not risk voltage sag damaging the cells on a drained battery when it switches to hover mode for landing (inevitably we all tend to land on a low battery).
One can add backup FC power from the VTOL if the cruise battery fails. I haven’t implemented this as it is a bit more involved and I don’t have the hardware. It is more of a future option.
The VTOL batteries need to be secured and I also need to create an anchor point for the sling load. I want this weight to be supported by the carbon fiber tubing/wings rather than the fuselage. I’m thinking maybe a polycarbonate or carbon fiber sheet tray and some sort of drop down brackets from the carbon fiber tubes that hug the sides of the fuselage. Carbon fiber would be lighter and stronger, but at the disadvantage of blocking Rx signals if too much is used. I want the anchor point on the belly of the plane so that it can pivot freely without making contact with the fuselage. Even a strong, thin plywood could be an option.
Photo: approx CG balance location of VTOL batteries
Polycarbonate is much more friendly to work with than carbon fiber and it also gives/flexes a bit (for better or worse). I’ll have to double up layers at the anchor point for reinforcement which is where CF has the advantage. Suppose I could do a PC tray with CF plate at the anchor attachment point. I require the tray to be removable/swap-able for flying imagery missions without a sling load. Decisions, decisions…
Happy to hear any suggestions others may offer on the matter.
Cheers,
Christian
My one concern is how little space you have left for payload options. The four battery packs take up a fair amount of space. What are you using for the R/C system?
Looking good Christian! One question…what airspeed sensor did you use? The mRo I2C HST-GH? I picked up one of these and it is larger in diameter than the recommended tube location on the wing, and looks to be too short to fit through the wing. Before we go hacking into it I was wondering if you used this sensor, if so how did you mount it? If not what sensor did you use that fit? Here are the guts of ours in progress…
I agree, dual battery does take up a lot more space. The 5000mAh packs are quite large, however, they are the biggest that would be in this VTOL and might only be in use for a handful of hover tests to see if the capacity is necessary. For light payloads, I’ll switch to single battery configuration with a higher C rating.
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