ADI

Hi A2,

Check back through the posts for Danvels new DF design. He used lower power GWS motor/gearboxes on his second machine. Can't remember the GWS model number.

Cheers ADI

Spaceclam

at what gear ratio? first of all, if you want to get the best power out of these, you must break the motors in. i would sugest something like 4 mins at 4.8 volts, just to round off the carbon brushes. it may be too late now however to break it in properly as you might have damaged the motors. also, the props are almost identical, true. however, the battery voltage will not always be at 7.2 volts. it looks like your GUESS (you need to know for sure, dont guess) of about 4-5 oz extra power is not enough. you should always keep a 1.5:1 power-weight at least. currently i am running 2.5 and it's a rocket ship. also, it looks like you may have to use different motors. they obviously do not produce enough thrust, and it's possible that at only 2 oz a battery cell at 2600 mah, that you are overstreaching the battery and it will not put out any more electricity. if you know what discharge your batttery is capable of, use that information to calculate the largest motors you can use and be sure to leave a bit of leway. you may end up having to just get some bigger motors and either a second battery to put in paralell or a new battery all together.

ADI

Hi A2,

For a start I'd get rid of the IRF540 fets. They have a very high RDS of 44 mohms and that's at 10v gate drive. They'd be even worse at 5v. In other words, some of your battery power is being disipated in the fets themselves, so the voltage seen by your motors is less than if you had low RDS fets.

Cheers ADI

Spaceclam

that could be it. if your thrust to weight is only 1.3:1 and you are loosing a lot of current in your mosfets there is your problem right there.

i'm kind of taking a break from working on the DF for a little while. my interest goes in cycles, and this is the downside. sooner or later i will get bored and i will get it flying, but i assure you i have not given it up. just need to take a bit of a break.

i've found some ideal magnets for these motors, 7x5x2mm. the problem is that still leaves roughly two milimeters of magnet sticking out of the back of the motor, and if i am going to sell these that could present a problem. i am not sure what to do here. it would cost a lot to get a piece of aluminum billet, and i would end up having to machine it down and i dont think i will have access to a lathe by then. i currently have access on saturdays from 9-12 AM because i am enrolled in the valley colledge metal shop course, but i have been working the machines for about 6 weeks straight, both saturday and sunday so the class is a bit behind where i am so i have a bit of free time, but i learned on a need to know basis and not a class thing so i am not sure how long it will be. either way it would pass on the cost of about $5 per motor, and i can not make enough of them to have a low enough profit margin for my time spent to make sense. my cost is about $35 per motor so to be competitive i would have to sell for about $60 apice and maintain about $25 profit margin. however, if i make say 4 of them, (which is about all i could do for a while due to initial cost restrictions) that would only get me Bout $100. also, until i spend about $60 on a speed control, i will be unable to test it to see what kind of thrust i am getting. i was able to use thrustHP but that is only for gas props and given the data shown on the link to the guys who did this, that would produce about 2 lbs of thrust, but again that is with a heavy, skinny blade, and that data was taken with the wires done in a WYE configuration. if i were to do it in a delta configuration it might be a practical choice for .40 size funflys. i have found the weight of the motor with all the magnets and stuff to be roughly 5 oz while a .40 size glow engine weighs abotu 8. i really dont know guys. if this works i can make maybe $100 but if nobody buys i am out a whole load of money, and i am afraid that becuase people know my age around there and they could get a name brand motor for only about $10 more that they will be skeptical and erro on the side of caution, buying a name brand.

tve

A2,

Just to add to ADI's input, you do have your FETs on the low side right?

A2

OK, I checked which gearbox I have on the GWS and it's the 5.9:1, I'm not sure if that's the best choice. I looked back at Danvel's motors and his were 4:1 I think. The FETs are on the low side, but I am thinking you might be right that they are not the best choice. I am thinking I will get some better FETs for starters and see what that gets me. The battery I am using is definitely not current limited, it supposedly can dump out 26 amps, so the problem looks more like my wussy drive circuit.

Thanks for all of your input, it really is appreciated. this thread is so dang long and there is an incredible amount of valuable info buried within!! It's sometimes difficult to remember everything that's been discussed and done. Keep up the good work ya'lls.

Later

danvel

Hi, A2.
Yes, my gearbox is 4.1:1. I know what happened to you; as the 10x4.5 todd's prop is not listed in gws's chart you chose what you thought it was the closer one (gws 10x4,7), but this GWS prop is noticeably wider than todd's 10x4,5 so that it requires higher reduction ratio.
With the 10x4.5, the 4.1:1 ratio is perfect for a 2 cell Li-Po setup. Of course weight is also critical (I'm at 320grams -11.4 ounces- with the battery included).
I think that replacing your transistors is necessary but it will not be enough. You'll have to either change your gearboxes to 4.1:1 or use a 3 cell Li-Po. You don't need 2400mah; 1500mah 8C kokam is enough because all four motors at full throtlle drain no more than 9Amps.

A2

Danvel,

yes indeed I see now what you are saying. DOH! what do you think about going down to 3.5:1 while I'm at it? would that be too much of a load on the motors with that prop or would it maybe give a little more headroom? I guess I got to get more parts now. I think that's half the fun, anticipating the UPS guy with your new loot! I'll try fixing the FETs too. sooner or later this thing is going to take off.

Thanks!

ADI

A2 Wrote:
>this thread is so dang long and there is an incredible amount of valuable info buried within!! It's sometimes difficult to remember everything that's been discussed and done>

Ain't that the truth ? Regarding the DF colaboration website idea that Space suggested: What about a simple portal type website with an introduction and a list of links to each of our own personal websites ? We can then just be responsible for updating our own websites.
The main portal site could still carry contributed articles and pics etc. Angelfire.com has free 20Mb server space with no max file size limits. Up to 20mb that is.

What do you guys think of this idea ?

Cheers ADI

Spaceclam

sounds good to me...

danvel

Of course, it is a good Idea. But who is going to be responsible of designing the portal and keeping it updated? Any HTML expert out there? I'd like to design a stylish web page for myself but I never find the time to do it properly (too many interesting electronics projects waiting to be studied).

A2: If I were you I wouldn't take the risk to order the 3.5:1 gerabox. Get the 4.1:1. It works fine.

ADI, TVE: Come on guys, I want to see your machines flying.

I am experimenting with a scrapped CD rom motor. I've repaced the magnets with N48 and I'm building a motor controller. My aim is not to get more power (my DF already climbs very rapidly) but to reduce current drain to increase flight time. What do you think about this?

Spaceclam

it's a great idea. i have been experimenting with those a bit, i have several here, but my main focus has been on capstan motors. i just happen to have two stators that are the same dimension except for thickness, but the inner diameter is too small to hold a bearing on one of them.[:@] maybe i can strap the secomd one on by winding it and use the other to hld the bearings? either way, i have open access to the valley colledge metal shop on wednesday, so i am going to cut some shafts. if any of you need me to make a small part, let me know before then.

ADI

Danvel Wrote:
>I am experimenting with a scrapped CD rom motor>

This is a great idea and yes, I agree the whole purpose is to increase efficiency ie. longer flight time for less power input.

I've finished building my new PCB for my DF version 2. Currently writing small temporary firmware code to test A/D and D/A etc onboard hardware. All tests so far OK with no problems.
Will post a pic soon.

I could knock up a small portal site for us, just to get started with something.
Time is the problem. Like you say Danvel ... too many electronic things to do first.

Cheers ADI

tve

Hi Danvel,

I have my flyer dis-assembled right now. I was moving all the electronics, motors, etc to the aluminum frame from my first flyer. I haven't had a chance to work on it for a while. I am considering scaling up and using AXi motors with 4-bladed Zinger props. As soon as I have some good video, I will post it!

tve

Spaceclam

TVE, don't use the zinger props! they will be very in-efficient! use either heli blades or the ones from braun modellbau.

jackblack24

Help with motor drive circuit - Hey Danvel and ADI - I was wondering if you could help me out with the circuit design for controlling the motor. I've been looking at H-bridge circuits on the internet but can't find one that will provide the Amps and Volts that I require (9V and hopefully 10-15 amps max). In a previous post one of you had said it was really pretty easy to make your own speed control circuit and I was wondering if you would either email me or post a circuit diagram showing how you did it. Thanks very much for your help!!

email: [email protected]

ADI

Hi Blackjack24,

Need more info. What type of motor etc ?

ADI

phoglite

holy crap this thread just doesn't end! I left town on business over 6 months ago and return to unpack my draganflyer and check out the old forum and - good grief! there are home brew draganflyers popping up right and left!

Regarding the idea of creating a web page - how about a wiki? Why not create the first "Open Source Draganflyer"? This forum format just seems too restrictive a medium... -phog

Spaceclam

did anyone notice the drop down page selection next to the skip page numbers?
i agree that the forum is too restricted. that's why i suggested the webpage. if it is not windy out this weekend, it should be a good 80 degrees. i could replace my spur gear and get the DF flying again!

Crac

Hi Flying Guys
Some (good) news of my "Draganflyer"... (vdo comming soon)

jackblack24

Here is my setup: I am running 4 SPEED 400 GWS motors directly driving 6x3 propellers. I'd like the speed controllers to produce 9V and the GWS specs say that I can expect 13.8 amps when running at top speed. My helicopter will be powered via a tether by either batteries or a AC to DC converter (not sure yet). Thanks for your help, it is greatly appreciated!!

ADI

Crac Wrote:
>Some (good) news of my "Draganflyer">

Magnifique mon ami ! or in English 'cool man'
Great to see another DF take to the air. We'd love to see some video.

Cheers ADI

ADI

Hey Blackjack,

You wouldn't use an H bridge arrangement to drive the brushed motors on a DF.
You'd use a single power mosfet and pulse width modulation control signal on it's gate to control the speed. One power mosfet for each motor. You could choose whatever battery voltage you like, within limits.

ADI

jackblack24

That makes sense. But here's my question: In my understanding a MOSFET makes the drain voltage equal the gate voltage. That would be fine except my PWM signal to the gate will only be 5V and I need to have 9V going to the motor. How can this be resolved? Or is my understanding of the MOSFET incorrect.

jackblack24

Also - should I use a high side or low side MOSFET? (what are the advantages etc). And What is the diode for in your circuit diagram? I assume it protects against something? Again I greatly appreciate your help.