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May 18, 2020, 11:18 PM
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Thread OP
Question

Use this brushed motor or go brushless? Sailplane


I have a beautiful vintage 12+ foot sailplane.
Its has a brushed ASTRO 05 Challanger Cobal motor.
Sailplane is not a speed machine. I will look up model name and add it to post later.

Should I replace this motor with brushless?
If so what kind or a limited budget?
(I do have several nice esc for brushless.

Or should I keep this motor and get a new brushed speed control. (missing)
What would be a nice one.?
And what battery combination would be good.

I thought I had the plans, so now I don't even know the model name.
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May 19, 2020, 12:04 AM
Retired Electronics Specialist
vollrathd's Avatar
Quote:
Originally Posted by SOARINGOLYMPICS
I have a beautiful vintage 12+ foot sailplane.
Its has a brushed ASTRO 05 Challanger Cobal motor.
Sailplane is not a speed machine. I will look up model name and add it to post later.

Should I replace this motor with brushless?
If so what kind or a limited budget?
(I do have several nice esc for brushless.

Or should I keep this motor and get a new brushed speed control. (missing)
What would be a nice one.?
And what battery combination would be good.

I thought I had the plans, so now I don't even know the model name.
I still have one or two of those old geared Astro 05 brush type motors. The were good for around 25 Amps and 7 Volts or around 200 Watts. I put them into a couple of sailplanes back in the mid 1980's.

Now days just about any decent brushless motor will put out 200 Watts, or much much more. What is the all up weight of your sailplane? Assuming around 75-100 Watts per pound of airplane, you're looking at a brushless motor of around 300 to 500 Watts. And, since the brushless motors do not have a gear drive off set, you may have to cobble up the front end of your model airplane to make it fit.

What ESC unit do you have? That will be involved in the motor, ESC and battery selection.
May 19, 2020, 01:12 AM
Registered User
Thread OP
I have a phoenix 80, or a phoenix ice 50, or a cheap r/c parts 30a
May 19, 2020, 01:35 AM
Retired Electronics Specialist
vollrathd's Avatar
Quote:
Originally Posted by SOARINGOLYMPICS
I have a phoenix 80, or a phoenix ice 50, or a cheap r/c parts 30a
Ah ha
Now, you will have a very wide choice of suitable motors for your model. Rimfire motors come to mind, along with many other motor manufacturers.

I have the Rimfire 42 motor on a large "Slow Ride" model. the Slow Ride model has a 63 inch wingspan with 1000 square inches of wing. It's weight is 63 ounces ready to fly. I'm running the model on a 4S1P 2500 mah A123 battery pack that is permanently mounted in the model. Field charging takes 10 or 15 minutes. A123's have no concerns about fire, no concerns about storage voltage, and they last many years.

I'm running the Rimfire 42 motor with a 13X6.5 prop, while pulling 40 Amps and 460 Watts on the A123 battery pack.

Rimfire brushless motors
https://www.towerhobbies.com/cgi-bin...motors+rimfire

Rimfire 42 motor.
https://www.towerhobbies.com/cgi-bin...?I=LXLWV3&P=ML
May 19, 2020, 02:04 AM
Registered User
scirocco's Avatar
It's a shame not to use the Astro as it is so nicely engineered, but the cost of a suitable brushed ESC and the performance gain from a brushless motor make it a compelling move to a new motor

Geared that's about a 230g drive. You could find brushless setups much lighter that could deliver the power, but with that short nose you probably need some weight anyway. The biggets challnge will be fitting an economical motor inside the nose - let's exclude geared options due to cost.

There are a couple of Turnigy GliderDrive motors that are almost no-brainer options for sports gliders. Either can handle enough power, so choose based on which one balances the model best. Unfortunately they seem to be out of stock at present. There are similar "outrunners in a can" with the connectors at the back from Axi Axi Cyclone) and others, but they are expensive

The lighter option at 142g https://hobbyking.com/en_us/turnigy-...html?wrh_pdp=2
The heavier one 180g https://hobbyking.com/en_us/turnigy-...html?wrh_pdp=2

If the nose is set up for a 42mm or bigger spinner, you might be able to get a 35mm outrunner to fit with enough wire clearance. If it's at least 35mm, a 28mm outrunner should fit, but will almost certaibly need balalst and wuill be working hard for a 12 foot glider, An example is the 88g Cobra 2216-21, which on 3S with a 12x6 prop will use about 240W - enough for a 4lb model.

A bulletproof simple solution but possibly a bit pricey at about $110 is the Mega 22/30/3E Run a 13x8 prop on a minimum 3S 1500 battery, bigger if it helps you balance. The castle 50A ESC will be perfect.
May 19, 2020, 12:29 PM
An itch?. Scratch build.
eflightray's Avatar
The main reason I haven't gone brushless with my motor glider is the weight difference. Brushless are generally lighter.

A brushed motor gives a perfect balance, (I'm also still using Nimh cells in it), going brushless means also adding lead, might be similar to change to Lipo cells.

'If it ain't broke, why fix it'

.
May 19, 2020, 06:18 PM
Registered User
If you replace it with a lighter brushless motor the weight of the plane will increase because the weight added to restore the balance will likely be behind the motor.
May 19, 2020, 06:23 PM
Registered User
Thread OP
Thank you.
Thinking about going brushless.
May 20, 2020, 08:41 AM
I'd rather be Flying
davecee's Avatar
I agree that brushless is the way to go. The only reason to stay with the Astro motor/gearbox would be for nostalgia. As for the balance situation. Buy a larger and heavier motor than needed, buy a larger and heavier battery pack than needed, prop it for appropriate power.
May 20, 2020, 12:16 PM
An itch?. Scratch build.
eflightray's Avatar
I hope you get a good advantage from going brushless, not just end up turning the same prop at the same rpm, ....... at a hefty price.

May 20, 2020, 04:44 PM
Registered User
scirocco's Avatar
Quote:
Originally Posted by eflightray
I hope you get a good advantage from going brushless, not just end up turning the same prop at the same rpm, ....... at a hefty price.

Remember the OP has no brushed ESC at present, but has several suitable brushless ESCs, so has to incur some cost either way.

Given the size of the glider relative to the 05 motor, I think it highly likely that a brushless solution is forward looking and will achieve much better performance, whether thrust, efficiency (allowing smaller battery or more climbs),or both.

A bit more information from the OP on physical fit would help with narrowing recommendations
May 20, 2020, 09:57 PM
Registered User
F2A1FAN's Avatar
Brushed ESC at Hobby King low priced.
May 20, 2020, 10:38 PM
Registered User
Thread OP
Thank you, the nose is about 1 1/4 inches, and there is about 2 inches aft of that.
By the way I measured the wind and it over 16 feet (5 meters)
I need to be careful not to overstress this old glider.
and I am not going to need a lot of duration for the motor, I get off tow just outside of pattern,
couple hundred feet and maybe a few relights.
May 20, 2020, 11:11 PM
Registered User
Thread OP
Correction 13 foot wing span.
May 20, 2020, 11:20 PM
Registered User
scirocco's Avatar
It looks like the old motor was clamped down to the block with the nose of the gearbox basically floating in the hole in the nose. With the existing structure and a rather skinny nose it could be a fair bit of work to mount an outrunner in there, which could tip the balance back in favour iof finding a 30A + brushed ESC.

But there might be an opportunity...

If the spinning part of a 28mm outside diameter outrunner could fit inside the nose , considering that with the prop driver fitted the actual motor can would be several mm back from the very front of the fuselage, a bulkhead could be installed across the fuselage at the right distance back from the nose, to rear mount the motor. The way the wires are in the wider part of the fuselage. The sketch below is the concept - apologies for the scrawl

It's just whether a 28mm outrunner can handle enough power to launch a 5m glider, but if the Astro 05 did it, a longer 28mm outrunner should be able to handle at least as much power


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