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Jan 12, 2020, 04:38 AM
Entropy is happening!
Jim.Thompson's Avatar
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Home made belt reduction drive.


I saw a picture of a very nicely manufactured belt reduction drive on a blog here somewhere that was going in a large, high powered aerobatic aircraft. I did not bookmark it and now cannot find it.
However, I did save a picture of the unit. I will attach it below.
I just found some small synchro drive belt pulleys on banggood which are designed for 3D printers.

https://www.banggood.com/GT2-Timing-...r_warehouse=CN

https://www.banggood.com/5MM6_35MM8M...r_warehouse=CN

I am wondering if they would be suitable for a medium powered set up. The motor would have to be carefully matched to the rating of the belt and pulleys and the propeller.
Engineering a working unit would be easy enough for me, but matching all the other components might not be so easy.
I guess it would be cheap enough to have a go at though. It would make for a lower revving, large diameter propeller on say, a slow flyer aircraft with low wing loading.
At least, that is one application that I am leaning towards.
Has anyone experimented with these small belt reduction systems?
If so, please relate what you know about them.
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Jan 12, 2020, 04:54 AM
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scirocco's Avatar
Your photo looks like the Stingr https://www.rcgroups.com/forufor ms/showthread.php?3494813-New-StinGR-Power-Unit&perpage=100#post43496819
https://www.rcgroups.com/forums/show...0#post42249921

Strictly for huge power throughputs
Jan 12, 2020, 05:23 AM
Registered User
Jim
Obviously perfectly feasible but compared to a low Kv direct drive brushless motor you have to consider any weight and efficiency penalties of a belt drive, particularly for a plane with a low wing loading.
Belt drive for IC engines can be attractive because a low speed high torque engine has a significant weight penalty over a high speed low torque type of the same power.
Jan 12, 2020, 05:29 AM
Entropy is happening!
Jim.Thompson's Avatar
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Quote:
Originally Posted by scirocco
..............................
https://www.rcgroups.com/forums/show...0#post42249921...........
Yes that's it.

Quote:
Strictly for huge power throughputs.......................
The example in the thread is, that's for sure.
Do you mean that the principle is suited for high power, or just the example?
Jan 12, 2020, 05:31 AM
Entropy is happening!
Jim.Thompson's Avatar
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Quote:
Originally Posted by Quorneng
Jim
Obviously perfectly feasible but compared to a low Kv direct drive brushless motor you have to consider any weight and efficiency penalties of a belt drive, particularly for a plane with a low wing loading.
Belt drive for IC engines can be attractive because a low speed high torque engine has a significant weight penalty over a high speed low torque type of the same power.
Yes, understood.
The idea was a rather spurious one thought up after seeing the banggood advert.
Probably not worth the proverbial candle.

Jim.
Jan 12, 2020, 07:53 AM
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scirocco's Avatar
Quote:
Originally Posted by Jim.Thompson
Yes that's it.



The example in the thread is, that's for sure.
Do you mean that the principle is suited for high power, or just the example?
I was referring just to the example when I posted, but even though I do use a lot of geared motors, I think there are relatively few special cases that could justify the weight, complexity and cost. For the vast majority of mainstream medium power models it is probably feasible to find a direct drive outrunner setup that is both effective and efficient, with the distinct lack of geared products on the market reflecting that. Gearing is generally only worthwhile when you can't get a low enough Kv within weight or space constraints, eg the skinny nose of a glider, or when the ultimate in high power efficiency is required.

A good low/medium power example (~4-600W) of gearing working well is high Kv 28mm helicopter outrunners geared about 5:1 for use in F5J gliders, where both limited space and low weight are important. The gearboxes cost 60-70 Euros and have several ratios. At that price it seems hard to justify the effort of designing and building a belt drive that is bulkier and less efficient,

Even situations where extra nose weight involved in gearing is a benefit, such as a short nose scale model, will probably do better overall with an oversized low Kv outrunner than gearing a higher Kv smaller motor.

My 2c anyway
Jan 12, 2020, 09:47 AM
An itch?. Scratch build.
eflightray's Avatar
Before I could afford brushless motors, belt-drives and brushed motors were my standard method of power.
Sadly they are now just dust collectors.

Bottom left is a pair of Modelair Tech belt-drives 3.6:1 that powered my B-25, 93" span.
Just above are the Olympus belt-drives, and top left the Olympus Mini-Drives, they us gears.

Things change, and I hate to throw things away, even when I know they will never get used again.

Ray.
Jan 12, 2020, 01:14 PM
Registered User
Why can't belt gearing be used with brushless motors?
Jan 12, 2020, 03:12 PM
Registered User
Belt gearing can be used with brushless motors but, generally speaking, it's not worth it because it's usually easy to get a brushless motor with a suitable kV for the particular application.
Jan 13, 2020, 07:03 PM
Greediest Suer
Ron H's Avatar
Generally is a good term to use. It may be worth it if you need to spin a big prop.
Jan 14, 2020, 04:52 PM
Registered User
One thing to remember is that low kv motors to spin big props tend to need more windings that need to have thinner wire and therefore have lower current capability ratings. Higher kv motors thicker wire = more watts, but you need the reduction drive to spin a big prop. The stinger was designed to do this.
Jan 14, 2020, 05:10 PM
Entropy is happening!
Jim.Thompson's Avatar
Thread OP
Quote:
Originally Posted by lrb75
One thing to remember is that low kv motors to spin big props tend to need more windings that need to have thinner wire and therefore have lower current capability ratings. Higher kv motors thicker wire = more watts, but you need the reduction drive to spin a big prop. ........................
I did not know that. I thought it was the opposite.
All that shows is how little I know about brushless motors, propeller sizes, and kv relationships...................

Clearly, I have much reading to do!
Jan 14, 2020, 09:51 PM
Registered User
Read this doc: http://www.sdp-si.com/PDFS/Technical-Section-Timing.pdf
Mainly the data tables at the end. And pay attention to the torque rating factors for short belt lengths. Although those values are for long belt life in industrial systems, so assuming you'll only be flying for a few hours a week, you can probably push it quite a bit harder. Service factor will depend on your flying style. Lower if you mostly just cruise around, higher if you frequently pop the throttle up and down doing fancy tricks.

If you have a 3D printer, use it to make the large pulley for your setup. Cheaper and lighter weight. Of course you can print the small one too, but the higher precision aluminum ones will probably result in less wear on the belt teeth, and higher torque capacity before jumping teeth.
Jan 15, 2020, 04:46 AM
Entropy is happening!
Jim.Thompson's Avatar
Thread OP
Quote:
Originally Posted by dekutree64
Read this doc: http://www.sdp-si.com/PDFS/Technical-Section-Timing.pdf
...................................
That's an informative document. I have downloaded it and saved for future reference.
Thanks.
Jan 15, 2020, 07:28 AM
Unregistered night flyer
kavic5150's Avatar
I'd like to see more gear reduction units for outrunners. Not so much for aircraft, but for ebikes and e-skateboards. Still working on my first ebike build here. I've already got a few belts, pulleys and even a keyed shaft for it.

Have yet to see an off the shelf gearbox for one of our Rc motors. At least not for ebikes. The only thing I'm finding is mid drive kits with their motor already installed.

These are just some pics I found for inspiration. The first one is the aforementioned Stinger power unit.


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