Flite Fest 2017: Bugatti 100P

[HilldaFlyer]

I just got a temp and RPM sensor for my Taranis so I'll be doing some bench testing. That with my watt meter and a scale I should be able to get a real nice data set for this motor (and others) at various prop sizes and input voltage.

With the contra setup I agree that you should easily be able to get 1kw. 5lb is a lot of plane to get moving 83mph on just 1kw, though. So I'll definitely be watching

Hey Nic,
When you set this up, I'd be very interested for you to start a new thread on the testing of motors. I have a thrust rig set up but I don't measure temperature (other than a hand-held IR meter). I go full throttle, record the Volt, Amp, thrust and RPM and trust that if I am under the Max Amp rating the setup will hold.

Having said that, I just burned up my first motor during the world record setting event at FF2016. I was using NTM 28-36 2200kv with 2200 mAh 40C and APC 7x4 prop. On the bench it draws 40A. The motor is rated at 50A. However, I calculate Max Amp from the power setting line I get 30A and 46A respectively. Emperically I have determined that the motor does not have a 50A max - less than 40 for sure.

Specs:
Model: NTM Prop Drive Series 2836 2200kv
Max current: 50A
Max Power: 310W @ 11.1V (3S) / 696W @ 15V (4S)
ESC: 40~60A
Cell count: 3s~4s Lipoly

This is the biggest frustration to me is how HK (or any other company) comes up with these numbers.

 

[nerdnic]

So, with the current draw from two motors this will be at least a 5000mAh ship. Voltage sag will not really be an issue. The pack I was using was a 2800mAh 4S pack. I forget the C rating. But anywho, I can do some bench tests, of course but they are more like synthetic benchmarks for computers. Not really practical for everyday use. The prop I used was actually a HK special. And here we go down the propeller rabbit hole.

The other MAJOR factor of the equation is the prop. APC-E props, IMO, should be banned from the hobby and melted into filament for 3D printers. I've preached their horrible nature to many many folks and I will reiterate here:
The blades are undercambered in profile... that means DRAG. They are horribly inefficient props for electric users and you will find better efficiency of your motors on other props. Equal thrust for less current draw. Further still, the material density is so high that it makes the MASS enormous for the size as well. If you can find a wood equivalent, do not even think twice. There is a reason why $20 props are on the front of my airplanes instead of $0.96 ones. Why do you think I've had motors for nearly 10 years?! And I'm talking about the high-end motors. Cheap Chinese knock-offs are fine so long as you take care of them. I balance my props EVERY time. I keep the bearings lubed EVERY season. I inspect for dirt nearly EVERY flight. Maybe its from my OCD but I will tell you right now that the prop is one of the major factors in making life easier on electric setups.

Ah this is interesting. Yeah props play a huge role in thrust, speed (RPM), amp draw etc. I don't have very much experience with all the prop options but this will be something I look into with my testing. Knowing the achieved thrust, RPM, and amp draw between various prop manufactures of the same diam and pitch is really interesting. You can have one 8x6 prop give you lower thrust, rpm and higher amp draw while another brand gives you more thrust, higher rpm and lower amp draw.

I've run APC-E and APC fuel props but not a whole lot else to be honest. It will be fun to dig into this a little more. I would say though that bench testing, while not 100% accurate to the results you get while in flight (This is actually something I'm going to test against since my whole setup except measuring thrust will fit inside a plane) they are valid for comparing one setup to anther. Whether you are comparing motors, props, batteries, etc, the data between the tests will be valid enough to show which setup performs best to the desired outcome.

 

[nerdnic]

Hey Nic,
When you set this up, I'd be very interested for you to start a new thread on the testing of motors. I have a thrust rig set up but I don't measure temperature (other than a hand-held IR meter). I go full throttle, record the Volt, Amp, thrust and RPM and trust that if I am under the Max Amp rating the setup will hold.

Having said that, I just burned up my first motor during the world record setting event at FF2016. I was using NTM 28-36 2200kv with 2200 mAh 40C and APM 7x4 prop. On the bench it draws 40A. The motor is rated at 50A. However, I calculate Max Amp from the power setting line I get 30A and 46A respectively. Emperically I have determined that the motor does not have a 50A max - less than 40 for sure.

Specs:
Model: NTM Prop Drive Series 2836 2200kv
Max current: 50A
Max Power: 310W @ 11.1V (3S) / 696W @ 15V (4S)
ESC: 40~60A
Cell count: 3s~4s Lipoly

This is the biggest frustration to me is how HK (or any other company) comes up with these numbers.

Yes I will be making a thread/article/videos etc. I have the 2200 and run it with a 7x6 on 3s, haven't burned it out yet but never tested actual draw. Also.. this is my last post about off topic stuff, I promise

 

[wilmracer]

So, if you go the single motor route for simplicity... I wonder how much effort and headache it would be to run 2 staggered props in the scale locations, but just run them in the same direction. Would probably be a torque nightmare but would give it a more scale appearance on the ground and in the air.

 

[localfiend]

So, if you go the single motor route for simplicity... I wonder how much effort and headache it would be to run 2 staggered props in the scale locations, but just run them in the same direction. Would probably be a torque nightmare but would give it a more scale appearance on the ground and in the air.

I've seen setups where the second prop free wheels. Should help with torque issues if going that route.

 

[willsonman]

Yeah, I could free-wheel a prop in front on a bearing without much modification... I really do not want to go there though. I have an email sent to a local friend who has serviced my car in the past and also races cars. I've seen some of the stuff he puts together and I'm hopeful he can help me out.

In relation to different Kv motors... No. Not planning on a difference other than prop. From what I've read (and remember) around the web you generally want a larger diameter and lower pitch on the front and a smaller diameter and higher pitch on the back. The reason is that the air passing through the front prop is then traveling at a higher angle of attack on the second one. So I could do an 8x6 on the front and cut down a 8x8 to a 7.5x8 for the back. This will increase the overall efficiency. Again... this is from memory and I need to find the reference for this.

 

[willsonman]

Measurements are in! The top of the bell can easily be tapped for the M10x1.5 thread. The stator can accept up to 12.5mm diameter so I think we have a rather solid plan.

Also of note is the inner rest of the bell. It protrudes 6mm from the top part of the bell and has an inner lip protruding about 0.7mm that rests on the inner race of the bearing in the stator. I think I should have the collet prop adaptor machined to have this as well so that it rests on the inner race of the bearing of the outer shaft.

 

[willsonman]

Now that I have a plan in place I've generated a parts list and estimated cost for just the motor. Raw parts are at $90 with capability of at least 1700watts. Even with shipping and having to pay for custom machining I'm getting a far better bang for buck over the Himax systems that are available. Landing gear hardware is $40 and an estimated $50 in airframe cost. Electronics are less than another $50. So the budget ofr this project is in the $250-$350 range. Really not bad.

My hope is to pick up some foam soon to start on the fuselage plug and wings. The foam scraps I currently have may allow me to get going on the tail planes but I've not had a hard look at my pile yet.

 

[Balu]

Didier just posted this on Facebook:

http://worldwarwings.com/news-reverse-engineering-never-built-wwii-era-plane-man-dies-test-flight/

Scotty Wilson was not ok with just seeing a static display however. Spending over $400,000 dollars and 10,000 hours building the replica, he achieved his dream 2016. With the first two test flights successfully completed, those close to Wilson said the third flight was going to be his last in this plane. After that, he was going to retire it and put it in a museum.

Sadly, on August 6th, 2016, it was his last flight but not in the same way. About a minute after takeoff, the 100P made a sharp bank to the left. Within seconds, the nose of the plane was pointing completely down and it crashed into a field. Wilson died instantly upon impact.

 

[willsonman]

The following refers to the attached cutaway diagram.

I wanted to better explain the motor as there seems to be a lot of question around how these things work.

The bottom of the diagram depicts one brushless motor that is affixed to the inner shaft. Its rotation is generated by its corresponding stator and supported by two bearings within the stator. This is all affixed to a standard x-mount.

The top motor is also affixed to a stock x-mount and will be bolted together with the bottom motor. The top stator will also have two stock bearings that will continue to support the inner shaft through the top stator.

This is where things get interesting. The top bell will need to be modified to accept a custom outer shaft. The outer bell will be drilled and tapped (screw fitting) to accept a tapped outer shaft. The outer shaft will screw into the bell and be secured to it using a nut on the inside of the bell. The threaded outer shaft will continue up where a prop will be reamed to go over the outer shaft and be secured with a corresponding nut at the top. The outer shaft will have two high-quality bearings to support the outer shaft (and corresponding bell) over the inner shaft. As this outer shaft/bell will rotate in the opposite direction (and have a separate ESC) these bearings will rotate double the speed of the other 4 bearings.

The inner shaft will be capped with a compression collet type prop adaptor with a brass bushing between it and the bearing for the outer shaft. This adaptor will also keep the outer shaft/bell in its proper vertical position.

Black areas are voids to prevent rubbing. This is NOT exactly draw to scale but provides a visual outline of what is going on. The lesson here is that one motor is spinning one way through a motor spinning in the opposite way.

The only modification here being a new and longer inner shaft, outer bell drilling and tapping, machined inner shaft with bearings. Its a very simple solution to a very complex setup.

 

[Craftydan]

This is where things get interesting. The top bell will need to be modified to accept a custom outer shaft. The outer bell will be drilled and tapped (screw fitting) to accept a tapped outer shaft.

Since you're having the prop adaptor machined to accept the narrower 4mm shaft and bearings, why not have the machinist drill and countersink the adaptor to match the bolt pattern already on the motor? All the work then occurs on one part, all the locations are centered off the same part and your machinist won't have to tap anything.

 

[willsonman]

I've thought of that Dan but the problem is that the current hole in the bell is a tight fit for the center shaft and it would need to be drilled out already. Machining a prop adapter with a bolt pattern would be more complex and require a larger piece of metal to turn down. This would also add mass that the bearings would need to support. I could probably drill out the outer shaft bell myself to allow the inner shaft to pass through as this would not need to be too precise with a bolt-on adapter. It would be a single-piece bolt-on solution but a much more complex one at that.

I've seen many home brew modifications done this way and it works but with a caveat. I've observed that when they do this a prop retaining washer is placed over the prop and 2 bolts pass through it and the prop, or around the prop, to secure it to the bell and create a lower profile. The problem with the motors I'm interested in is that the bell has three supports and is not ideal for a 2-blade prop/retaining mechanism. I'd have to have a back plate machined into the outer shaft to accept that and would create a LOT of waste metal in the process.

 

[Craftydan]

hmm . . . I was half envisioning you were using a bearing on the bell to pass the shaft through then using a short-shaft style adaptor to attach your outer-shaft to the motor.

Yes, a lot of waste material to machine that, but I don't think you'll find a better way to attach a hollow shaft squarely on that bell and still hold the bell constrained in space. Dunno about the bolt pattern already built into the bell, but if it's not too close into the outer shaft's diameter it's better to use those holes than leave them in and drill new ones.

As for the two side-bolt-through prop setup . . . why would you even need an outer prop adaptor for that? put a bearing in the bell for the bell to spin around the inner shaft, retaining clip to hold the bell's bearing fixed in space, then attach the inner prop to the bell using the two bolts, with the inner shaft and retaining clip spinning freely inside the prop hub. You'd need to move to a different motor model, carefully select and prepare the prop, and you'd need to ream out the motor bell to fit a bearing and cut the long shaft, but the setup is by far the least complex to machine.

 

[willsonman]

One of the main issues I've found is finding bearings that will fit in these small places while being robust enough to withstand the forces involved. The stock prop adapter simply cannot accommodate a bearing at the top end and be hollow. With the force involved with a M10x1.5 shaft I would have about 0.5mm wall for the bearing to seat into and the max depth of 2mm for the bearing. Moving to a M12 shaft allows for a thicker wall and a deeper bearing to support the rotating bell. This means I have to ream out a prop quite a bit but that is minor compared to the complexity of milling out an adapter. I'm sure if the bell is reamed and tapped on a lathe things will spin true once the outer shaft is put in place.

Getting the props fairly close together is an issue separate from this. I may have to cut into a grub-style adapter for the front prop but I'll cross that bridge when I get there.

 

[willsonman]

For those who may be doubting the effects of contra setups I remembered a video I saw awhile ago and I've found it to share here. While the entire segment is interesting, the last bit starting at 12:41 is relevant to the project.

 

[Aeronaut]

A full scale aircraft company using hobby king thrust stands who knew? Do you know if they ever got it flying?

 

[willsonman]

Not yet, as far as I know.

 

[OttoPilot]

One of the main issues I've found is finding bearings that will fit in these small places while being robust enough to withstand the forces involved. The stock prop adapter simply cannot accommodate a bearing at the top end and be hollow. With the force involved with a M10x1.5 shaft I would have about 0.5mm wall for the bearing to seat into and the max depth of 2mm for the bearing. Moving to a M12 shaft allows for a thicker wall and a deeper bearing to support the rotating bell. This means I have to ream out a prop quite a bit but that is minor compared to the complexity of milling out an adapter. I'm sure if the bell is reamed and tapped on a lathe things will spin true once the outer shaft is put in place.

Getting the props fairly close together is an issue separate from this. I may have to cut into a grub-style adapter for the front prop but I'll cross that bridge when I get there.

Have you looked at dental bearings or solid bushings yet?

 

[willsonman]

Solid bushings are a no-go due to side load constraints. Dental bearings... Not paying for those.

 

[Michael9865]

For those who may be doubting the effects of contra setups I remembered a video I saw awhile ago and I've found it to share here. While the entire segment is interesting, the last bit starting at 12:41 is relevant to the project.

Wow!! Somebody needs to affordably start making those setups like he showed in the video. Off topic, but can you imagine a contra rotating ducted fan? After watching that video my mind is blown. I can't wait to see yours completed.