Reversible brushless ESC

[Kernwrech]

Hi there!

I'm currently building a 5-foot indoor blimp. It will have only one motor and propeller with some kind of vectoring system. What I need is a lightweight, reversible brushless speed controller. I know I could change the rotating direction of a brushless motor by swapping two wires, but I need it to have throttle for reverse also (motor stops when the throttle stick is in the middle). Is there any models than can do this? Or do I need to resort to PICs to get it working?

[Zlatko]

Hi,

I am not sure what weigth you can cope with, but the only one that I know is revirsible is the Mamba by Castle Creations as used in RC Cars (0.9oz / 24.5g ) .
http://www.castlecreations.com/products/mamba.html

Cheers

EDIT ...
I think some of their boat ESCs are revirsible too but much too heavy.
Have you considered one of those variable pitch props ( in flight adjustable )?

[Acetronics]

Redirected

[jeffs555]

This one is only 14.4 grams, and you could probably remove the plastic case to make it lighter. It is only rated for 7 nicad/nimh cells so would probably be limited to 2S lipos.
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXCNR7

[Kernwrech]

It would have to be less than 20 grams. I will use homemade brushless motor (around 5 amps), which is light enough. I have seen many brushless ESCs with a weight much less than 10 grams, but these are not reversible by traditional means (one can always reverse a brushelss motor by swapping any two wires of the three).

variable pitch prop would be too heavy and too complicated for the size I'm aiming to. Besides, I still would need a speed controller, and one extra servo to adjust the blade angles. Vectored thrust and reversible motor seems to be the only sensible option.

[Acetronics]

This one is only 14.4 grams, and you could probably remove the plastic case to make it lighter. It is only rated for 7 nicad/nimh cells so would probably be limited to 2S lipos.
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXCNR7

BRUSHLESS ONE ?????????????? :confused:

[A.T.]

Hi there! I'm currently building a 5-foot indoor blimp. It will have only one motor and propeller with some kind of vectoring system. What I need is a lightweight, reversible brushless speed controller. I know I could change the rotating direction of a brushless motor by swapping two wires, but I need it to have throttle for reverse also (motor stops when the throttle stick is in the middle). Is there any models than can do this? Or do I need to resort to PICs to get it working?
Quark 22A ESC for Brushless motor - Forward and Reverse for boats.planes & Heli 7 modes (http://www.acehobby.co.nz/ossb2/main/Productfinder.asp?ID=53233)
Refer to Sky & Technology web page for full range available and set up demo video.
Regards
Alan T.
Alan's Hobby, Model & RC FAQ Web Links (http://homepages.ihug.co.nz/~atong)

[Kernwrech]

Hmm... that one is still a little bit too heavy, besides, it is rated for 22 amps, which is more than I'll ever drain from the battery. Also the price is something I cannot afford, being besides impossible to get from my country.

Any other ideas/ setups that might work aside from reversible ESCs?

[xtal]

Theres a bi-directional on Bruce Abbotts website... check it out

[Kernwrech]

Sorry, but that is not for a brushless motor...

I need reversible, single channel brushless esc that is lightweight and preferrably fits in a small-budged project.

[Neil Stainton]

I'd try th Mamba, it will probably only weigh 12g-16g with the heat shrink removed and lighter, shorter wires. You could probably save another 1-2g repacing the cap with a smaller SMT one. If this controller weighs too much you will find it easier and quicker to shave 5g off somewhere else (eg use 2.5g servos), rather than mess around trying to find or build a lighter controller.

[Kernwrech]

The mamba would be good but it doesn't fit my budget. It costs more than 100$ here, more than my other RC gear combined!

I was looking for something around 50$ tops

[Malc C]

Personally I don't think you'll find what you are looking for for the amount you want to spend. Most controllers designed for aircraft only feature forward control as that is all that is required, so reversable controllers are generally aimed at cars and boats where weight or size isn't a factor in the performance to the same degree as a light weight heli, plane or blimp.

Yes you can reverse a brushless motor by swapping two wires, so in theory using a double pole, double throw relay could be used to change the "polarity" from a single directiction controller via a RC switch and another channel on the TX, however the combined weight of the PC switch, a relay large enough to handle 5Amps at 12dc and the controller would not make it a viable alternative.

maybe the alternative would be to fit the motor on a spindle and have a servo rotate it to provide the direction. I've seen the use of a large puley wheel on a servo and a small one on the item to be rotated work well enough to give almost 180 degree rotation

[Neil Stainton]

Another option is to use a brushed DC motor, not a brushless, there are many more forwards/backwards controllers available, or you could build one easily.

The cheapest way would be to dissasemble a standard R/C servo. Remove the motor and servo amp, and use the first set of gears to gear the motor to a small prop. You will get a r/c controlled reversible motor for a few $.

Neil.

[Bruce Abbott]

I was looking for something around 50$ tops
ELE E-Hobby-A-30A (for car W/Reverse ) (http://www.elemodel.com/shop/html/product_1299.html), $37.88.

Specified weight is 22g, but you could easily lighten it (remove heatsink and filter caps, replace wiring etc).

[Kernwrech]

...
Brushed motors can never reach the efficiency of the brushless ones. Besides, brushless motors have much better power-to-weight ratio. I have built a brushless motor from CD-rom drive parts with weight less than 16 grams and 30Wats of power. the brushed motor of same power would be about twice as heavy and noisy. Besides, I would need a reduction gear for the brushed motor to turn a large prop, further increasing the weight while outrunner brushless woundn't need any gear.

Using brushed motor my blimp would be underpowered (it's ok for a indoor blimp, but with powerfull motor it could lift heavier loads). That's why I would need reversible controller for brushless motor. The regular 8A brushless controller has typically a weight of 5 grams without cables, so the whole power pack would have a weight of 30 grams tops.

But as far as the availability of the parts goes... doesn't seem possible to achieve. If I'll use standard brushless controller, I'll need to be able to vector the thrust at least 270° to have full controll. Actually, I don't need a controllable reverse, a on-off reverse would be sufficient, since the reverse would only be needed to slow down airspeed. with this kind of setup 180° would be sufficient. the only problem with this setup would be to arrange the reversing mechanism. Any ideas?

[vintage1]

...
Brushed motors can never reach the efficiency of the brushless ones. Besides, brushless motors have much better power-to-weight ratio.

1/. They can. Brushless motors are only brushed motors with electronic commutators. ESC's have their own inefficiencies as do brushes. The fact that most brushless motors are made with neodymium magnets and ball races and most brushed are not, is the real reason why they are so much better.


2/. In fact the second statement is saying nothing new. The greater the efficiency of a motor the greater its power to weight ratio.

[Kernwrech]

the point here was to pint out why to use brushless motors.
Another was to come up with a system that would work.

[Comatose]

Its not going to happen - reversing brushless motors either need to be sensored or know what motor they're mated to in order to use some information about the motor (saliency, for example) to commutate at low/zero speed. Otherwise, they have to operate as a stepper around zero speed, but that is very rough and extremely inefficient.

If you look where the brushless car ESCs are going, most are sensored except for Castle's mambas, which they supply with the appropriate motor.

[Neil Stainton]

Also have you actually made a 5ft airship before? I VERY much doubt you will need the power of a CD ROM based motor for indoor use.

[Aeroengineer1]

I have to say that the mamba controller is very nice, and contrary to what has been said about it only working with the supplied motor, that is not true. This is a very nice controller that I am using in model submarines. If you do a search, you can find them for cheaper. Typically the are going for $75, but you can find them for about $60 if you look long enough. I am running an IPS sized motor with mine right now with no problems in the transition between forward and reverse. Though I would admit that it would be nice if someone did come up with one smaller, but there is no market for it.

Adam

[Kernwrech]

Hi!

Neil, I haven't done a 5ft airhsip before, but even one of those ricegraind sized motors would move it indoors. The problem here is that I need the power to have high load capability (to lift even 50 gram overweight off the ground). This would need to be only momentary.

Another point was to have enough power to be able to fly outdoors in slow winds. outdoor flying requires much more controllability since there are drafts and turbulences all over. Since the airship is so small, it would need very powerfull engine to fly safely out of a gust of wind. Brushless motor might just be it :D

And when we start to consider using a brushed motor (like a pager motor) of the same weight, we'll see it doesn't have nearly as much power. So this weight goes wasted. The whole idea here is using the lift I have from the lifting gas (that's about 100 grams) to its full extent. Having a strong motor with vectored thrust would aid take-offs if the blimp has some extra weight to carry (like a wireless camera or an advertising blanket)

Adam, If I could get mamba for 60$ somewhere I would be satisfied for the price. The problem is that There's only one radio shack that sells these around here, and the price is almost 110$ I would (again) have to look for them abroad, and the price easily grows when we start to consider shipping of a single part etc. the same old story...

If i move from reversibility to vectored thrust, how hard would it be to build 270° pivoting? My micro servos go 180*, and have 0,8kg of torgue. if the vectoring goes 270°, it can push up, back, down and forward (plus all the intermediates)

[Comatose]

You don't need 270 degrees if you go to a variable pitch prop- you only need 180. Set it up so up and forward use forward thrust, and down and back use reverse thrust. Viola!