50 foot Big Floyd - Page 92 - RC Groups
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Sep 08, 2005, 05:04 PM
Thanks Wilber and Orville !.
sonic liner's Avatar
I just threw away an electric scooter yesterday from a load i hauled to the dump
for someone. I started looking closer at it and it had two 12 volt batts and alot of
good wire, i then salvaged.

One pilot asked about the 10 speed chain idea, a good one too, but this setup
looked perfect for your aplication, the motor was a 24 volt, but it said 20 amps
max on it so i tossed it, anyway the chain, output sprocket and rear wheel sprocket
looked perfect, perhaps you can visit your local bike shop for some ideas on the scooter parts. They seemed pretty heavy duty for their size, and could propel
a 150 lb rider.....Reminds me of the wright brothers....Flybike...flying bike.

Hans....... Just a thought, check it out......Pete Lane
Last edited by sonic liner; Sep 08, 2005 at 05:34 PM.
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Sep 08, 2005, 05:06 PM
Registered User
Neil Stainton's Avatar
Hovertime, you need to give the battery size and both the motors' Kv, Io, and Rm if you want help. I presume you are choosing the optimum prop for both motors? And the brushless motor's Kv isn't appreciably different from that of the brushed motor?

Sep 08, 2005, 05:48 PM
Always right
Hovertime's Avatar
Hm guys, never mind, found that I have missed something - as speed increases brushed motor unloads and rpm goes up, while brushless holds rpm much better under load, and does not increase RPM much as speed goes up, resulting in reduced performance at flying speed. While BL in this calculation has more static rpm , it has less rpm at flight speeds...

Thats what I get for being used to just look at performance prediction line and first line of data - static thrust....
Oh well, learn/relearn something everyday

PS - this was just an academic exercise BTW-motors/batteries/airplane was taken out of the blue.
Sep 08, 2005, 07:42 PM
Registered User
koko76's Avatar
Originally Posted by JWarren
Was there any thought to using bicycle chain and sprockets from a 10 speed bike? I am sure the machine shop at your school could adapt them to the motors and prop shaft. Just a thought.

There was thought, but chain drive is not as well suited to this type of drive as might be thought. Most of the shortcomings have been covered earlier in this thread, but suffice to say compared to belts in this app, chain is not what we want, and bike chain is even less what we want Chain comes in many pitches (as of course do belts). Bike chain is designed for easy derailment during shifting, which we do not want. It is close in pitch to #25 chain which is also fairly sensitive in the misalignment department. #35 is a much better choice for this app, but the required sprockets to get to the reduction are huge and heavy. I use a 6:1 #35 chain reduction on my micro go kart. I have a 9" wheel on that, and when I let the tire get a tiny bit low the chain rubs the pavement.
Sep 08, 2005, 08:56 PM
Just one more plane!
JWarren's Avatar
I was thinking about that V motor configuration gearbox.

Then I also thought that the tourque on everything would be very high without the use of a centrifical clutch of some kind. Too much metal.

Here's another thought...... Get someone to rewind a small paddle fan motor and do away with the gearing all together.
Sep 08, 2005, 09:07 PM
Always right
Hovertime's Avatar
But we already have perfect power plant ! That just needs some tweaking, thats all!!
Sep 08, 2005, 09:40 PM
FlattyFlier's Avatar
With such a big and slow plane, we need more thrust(like what you get form a BIG prop spinning at a lower RPM) rather than lots of airspeed from a much smaller prop spinning at a much higher RPM.

Just like a Slow Stick with a DD 300 compaired with a geared 300...

The little prop of a DD motor configuration, although will be putting out more thrust, the thrust would be concentrated right behind the prop's diameter, which wouldnt be large enough to efficently pull such a big bird.
But a much larger prop at lower RPM would still give almost the same amount of thrust but with a much wider area, which will pull a bigger or slower(in this caes its both) plane better and also pull less power from the batteries!

We have the proper amount of thrust from the 3 geared motors, we just need to find a belt or something of that nature that wont strip under all the torque, as Hovertime said.
Sep 08, 2005, 09:49 PM
Sink stinks
Montag DP's Avatar
Any progress with the power plant? Sorry, I don't have time to read the part I missed because school is back in full swing.
Sep 09, 2005, 01:48 AM
Just one more plane!
JWarren's Avatar

The bearings in one of the AXI's crunched out due to the belt pulling on the shaft. The belt pulling on the shaft may have also caused the magnets to come in contact with the stator causing the sounds Hans was hearing. I did not the find the Video he spoke of, so I really can't say for sure. Just a guess.

So, take the belt off the motors shaft and put it on a pulley. The pulley will also keep the teeth of the belt from sliding over the top of the teeth on the pinion gear. You only need teeth on one side of the belt with this configuration. A more heavy-duty automotive timing belt may be a better solution with this arrangement. I added a quick (not so good) image of what I am suggesting and should be an easy mod. The drawing may not be exactly the same as the existing gear dive unit, but may give you an idea of what I am thinking.

Orange = motor pinion gears
Red = pulleys
Green = the belt
Black = prop adapter

With angled bearings and races like those found on the axels of cars. The retaining nut should not be allowed to torque down on the bearings. The nut should be hand tight only with the cotter pin and sleeve over the nut to keep it from turning.

Just another thought.
Let me know when you get tierd of my thoughts. Just trying to help.

Sep 09, 2005, 01:50 AM
Registered User


Sep 09, 2005, 01:54 AM
Just one more plane!
JWarren's Avatar
Hi dmoran,

You don't have to post to subscribe to a thread. Just scroll up to the top of the page and use the thread tools button, then click on subscribe.

Eric (koko) check out post #1374

Sep 09, 2005, 02:14 AM
Registered User
koko76's Avatar
Originally Posted by JWarren

The bearings in one of the AXI's crunched out due to the belt pulling on the shaft.
No they did not. Posts after that indicate the real cause of this issue. No bearings failed, the only bearing problem was of the main bearings seizing, due to a self tightening (yes mistake on my part) mainshaft. There is not any issue of sideload on the axi's, never has been.

I'm not keen on fixing what ain't broke, so I really don't see the need for any drastic changes beyond that which failed, namely the mainshaft problem (easy to address, I'll just do it the way I initially planned before I got sidetracked). The other two issues are using a belt of the full width (belts were not in stock at the time) speced initially, and that the adjustable motor mount perhaps could use a tensioner pulley. We shall see how that one goes, and it's last on my list of things needed to solve the problem.
The bearings used were in fact tapered roller bearings, and the nut in question did tension those bearings as it needs to be done for this bearing type. The problem was that I used the prop adapter as part of the nut, the equal and opposite reaction thing of the prop trying to resist spinning caused the tightening forces. I had it worked out in my head so that the thread would unthread and used a jam nut to prevent it. Needless to say I had it worked out backwards. I have a simple and easy solution all worked out though
Sep 09, 2005, 02:43 AM
Just one more plane!
JWarren's Avatar
I meant no disrespect Eric!

You do fantastic work!

I missed the info on the motor bearing. This thread is getting so long................

I'm glad there is a simple and easy solution and you don't have to pump a lot of time into it!
Sep 09, 2005, 07:45 AM
What...me worry?
bluswede's Avatar
Koko, (Eric?)
I have a fair background in physics, machinery, and a 20-year-old associates' degree in mechanical design that I take out of the closet on occaision, just for "kicks". I've held your belt drive in my hands...did the post mortem with Hans after the flight attempt. DANG!...those tapered bearings were tight!...that prop was effectively an impact wrench as the teeth on the belt jumped/were stripped. Reversing the threads, like you just posted, should do the trick, provided that the motor controllers are set to soft cutoff with no brake. Perhaps you could add holes in the hub for "tommy bars" so it can easily be held whilst the jam nut is tightened? There wasn't a strap wrench available.
I could see that you put a lot of thought into the drive, and some fine workmanship...really liked that you milled out those areas in the main plate to reduce weight, still leaving beefy webs between the motor mounts and mainshaft bearings, slick!
I also saw what looked to be plenty room for idlers on either side of the top (adjustable) motor mount, should you deem that necessary to get more belt "wrap" on that motor's pulley. You'd get a couple more belt teeth sharing the load...could make the difference if the 15mm belt still strips. There's a PILE of shearing force on the belt teeth with 1/3 of roughly 8 horsepower going through those small-radius motor pulleys. Going from four teeth sharing the load at 120 degrees wrap to six teeth sharing at 180 degrees wrap cuts force per tooth by 33%, nothing to sneeze at! I was thinking flanged ball bearings pressed/seated into bored-out standard pulleys and idler shafts pressed into holes drilled and reamed in the mount. Idler shafts having shoulders and threaded on the ends such that a loctited nut will retain the idlers. Given the angles involved, the sideloads would be relatively small and you could prob'ly get away with a pretty small shaft (3/8"?) and bearings...say 1/4 inch BRG bore with 11/16inch outer diameter/pulley bore. (just a guess...no math done)
Replaying the flight attempt in my head, I remember that the prop seemed to freewheel for quite some time (couple, three, four seconds?) after the throttle was cut...Hans?, is this your memory also? If that is, indeed, the case, the propeller's momentum was turning a shaft that I couldn't turn without a "cheater bar" a foot long. That prop is really light! (also a nice piece of work!) I know the math, but it's still amazing what happens when something relatively light gets spinning...it stores a bunch of energy!
Just my two cents...Heh!, if you could collect all the "two cents" you've gotten here, you be on easy street!
P.S.: Some of my work...really need a mill and lathe the size of yours...check the size of my lathe chuck!...that's a piece of 2" 6061 round barstock!

EDIT: Things are straying a bit far from this thread...not my intent with this post. I've started a new one here: https://www.rcgroups.com/forums/show...611#post4288763 Feel free to share lighthearted stories of destruction and mayhem...words of so-gained wisdom...and anything else you just can't keep to yourself anymore! Or ask/comment about my stuff.
Last edited by bluswede; Sep 10, 2005 at 04:18 AM.
Sep 09, 2005, 08:02 AM
Registered User
koko76's Avatar
I've done much work on a Sherline that shouldn't have been done on a machine of that size. If you look at some of my robots http://geocities.com/kokop76/robots.html you can see some of what I've gotten away with. It's only within the past year that I've come into access to the tools that I really need to be dangerous. Of course there's still more like the waterjet, my own sheet metal tools, a laser....All in good time.

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