RC plane motor questions

I've been interested in small brushless motors for some time and it seems like the ones made for RC use are plentiful and cheap. Bujt I'm
having a hard time getting my questions answered about these things. My uses will not be in some type of RC toy, but "toys" that I want to make for myself. I know I will need to get an ESC to drive the motor. But what kind of signal does the ESC need? The same type of signal that RC servos use? Do I need to get a programming card for the ESC? And how is the rpm/volt detrermined? I'm thinking that I should get a kit motor to learn about them but I also want to get some regular motors to compare. It looks like Hobby King might be the best place to buy the motors from but I don't know. Any help would be greatly appreciated. Thanks, Eric
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On Thu, 23 Jun 2011 16:18:39 +0000 (UTC), snipped-for-privacy@whidbey.com wrote:

A plain, normal ESC will use the same signal a servo uses. It connects to the receiver just like a servo. There are also special ESCs that are controlled by SPI or similar. These are used where very quick response times are needed.

It depends. Some higher-end ESCs allow you to tune their parameters, but they come preconfigured to working defaults, so will work fine in most applications. Some ESCs are programmed using the throttle stick in connection with beeps emitted through the motor, some need a programming card, while others are connected to a PC. Some controllers cannot be reconfigured at all.

It is determined by a number of factors, such as magnet strength, number of windings, number of poles, physical size, and more.

I've never built my own motor, so I can't help you there.

I have not (yet) dealt with them, but I have heard from numerous happy customers, so they seem to be a decent outfit.
--
RoRo

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On 06/23/2011 10:10 AM, Robert Roland wrote:

That's pretty much what I would say. The only exception is that the stuff Hobby King sells can have quality problems, both the kind that causes infant mortality, and issues with long-term reliability and robustness. If you really want it to last, particularly if you're stressing the bearings in any way, Hobby King's products may not be the best.
AXI, eFlight, Scorpion, Castle Creations, and Plettenberg are all better (1st tier, or almost so) motor brands that I know. But they're more spendy -- use the Hobby King stuff to get your feet wet, then go from there.
--

Tim Wescott
Wescott Design Services
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wrote:

Thanks Rob, Winston, Cy and Tim, I knew there would be someone here who would be familiar with these things. I have two projects in mind. The first is a gyroscopic stabiliser for a digital camera. I built a prototype with brass flywheels and pager motors. It worked OK but the life of the pager motors is low. And they were a little noisy. So I'm thinking that maybe one of these new fangled three phase brushless motors used with good bearings might work. I seem to remember downloading a circuit built around a 555 timer that puts out the pulses used by servos. So with a cheap ESC, LiPo battery, and brushless motor I might be able to make a lightweight gyro stabiliser. The other project that I've been working on is a spinning wheel with a brake on it. The idea is that when the brake is slowly released the wheel will start to spin, with less braking leading to faster spinning. So I need a motor that can remain stalled without overheating. With a stalled brushed motor the energy delivered is not shared equally by all the windings and so maybe it will overheat. I don't know if the three phase brushless motor drives keep energising windings in sequence when the motor is stalled. This something I want to find out. Eric
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On Jun 23, 3:07 pm, snipped-for-privacy@whidbey.com wrote:

How are you dynamically balancing your rotors? Have been looking for a small dynamic balancer that could be built by an individual without bankruptcy staring me in the face. Would be of interest for doing a bunch of projects involving high-speed revolving parts. Think model turbojets...
As far as stalled rotors, a friction clutch is the usual solution, motor doesn't see a real current spike that way. Just have to replace the clutch if you wear it out from stalling too frequently.
Stan
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On Thu, 23 Jun 2011 14:27:29 -0700 (PDT), snipped-for-privacy@prolynx.com wrote:

Greetings Stan, I'm trying to avoid slip ctutches. For a couple reasons. First, they wear out, and second they tend to have higher breakaway friction than running friction. I can buy special clutches that do not exhibit this stick/slip problem but they are expensive. If anything the breakaway friction should be lower than running friction. I'm hoping that I can run a motor at a much lower current than it is rated for and so can keep it stalled indefinitely. I didn't balance my rotors for the gyro. They were machined carefully and all at once except for a facing cut after being parted off. The parallelism was better than .0001" and concentricity was basically perfect because all diameters were machined at the same time. Cheers, Eric
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wrote:

You might want to check out the gyroscopes used in R/C helicopters to stabilize them, they are real gyroscopes except they use vibration to sense rotation instead of spinning a flywheel. The vibrating crystal resists rotation just like a flywheel or pendulum would, it's called the corollis <sp> or similar (from memory) effect. These electronic gyros are used in r/c helicopters and also things like the steady-shot in digital cameras. I bought a couple of Murata gyroscopes several years ago but haven't done much with them yet, future project though....
RogerN
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wrote:

The purpose of my gyros is to do the actual stabilising. The gyros used in helicopters are sensors. In my Sony camera is some type of physical lens positioning system that uses some type of motion sensor for positioning info. However, it is not enough for more violent shaking. I have a relative who loves to take pictures but has hands that now shake so much that some type of stabiliser might really help. Eric
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snipped-for-privacy@whidbey.com wrote:

Back in the late 1970s, when living in the US, I saw IIRC mil surplus gyroscopes for stabilising binoculars on sale in some magazine, can't remember which but they may still be around. At the time I was involved in archery and using a 95 lb long bow and took the piss out of the target archers and their pulleys and stabilisers and such and suggested they fit some. It wasn't long after I saw someone doing just that. It was about the same time I realised the mental side of any target sport as shooting at a standard size archery target would result in a given group then placing the likes of a bottle cap in the middle of the target would result in a consistently and significantly smaller group, the smaller target resulting in greater focus.
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On Jun 23, 5:07 pm, snipped-for-privacy@whidbey.com wrote:

Instead of screwing around with 555 circuits, you really ought to consider a microcontroller. Making servo pulses with an AVR is super- simple, maybe ten lines of code to get it set up, and from there, you just change a register value to pick a new speed. With one of the AtTiny parts, you'd actueally have fewer components than you would with a 555.
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On Thu, 23 Jun 2011 18:12:31 -0700 (PDT), rangerssuck

I know how to control a servo with a microcontoller. The 555 solution is, I believe, cheaper. Eric
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On Jun 24, 11:40 am, snipped-for-privacy@whidbey.com wrote:

maybe, but not by more than a buck or so.
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On Fri, 24 Jun 2011 09:18:41 -0700 (PDT), rangerssuck

I bought a Basic Stamp kit from Parallax and learned how to control servos with a microcontroller. I'm not sure how use a pot to vary the pulse output rate from the stamp. But I can do this easily with a 555. If I needed hundreds of motor drivers I wonder what would be the best way to go. If I just wanted to control no load speed and direction without any type of feedback from the motor could a microcontroller do that by using power transistors? Easily and cheaply? Since I haven't even ordered a motor and ESC yet these questions may be premature. Eric
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On Fri, 24 Jun 2011 19:08:45 +0000 (UTC), snipped-for-privacy@whidbey.com wrote:

These motors cannot practically be driven without feedback, but you could very well use the micro to handle the feedback as well. In fact, all the commercial ESCs I have seen close up use not much more than an Atmel microcontroller and a bunch of power MOSFETs to do the job. If you had access to the firmware, you could simply modify it to read a potentiometer directly in stead of reading the pulses from the RC receiver.
If you want to build your own, you can find several open designs where both hardware drawings and source code is freely available.
--
RoRo

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Robert Roland wrote:

Why bother with a pot? Actually, there are several solid state 3-axis accelerometers available. Parallax has one - pretty reasonably priced.
--

Richard Lamb
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On 06/23/2011 02:07 PM, snipped-for-privacy@whidbey.com wrote:

Why control motor speed with a brake when you can control it actively? Get an ESC that has a helicopter mode, program it right, and it'll give you a specific RPM at the motor for a specific pulse width at the input.
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Tim Wescott
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On 06/23/2011 02:07 PM, snipped-for-privacy@whidbey.com wrote:

Note, too, that most ESC's won't just start up and go -- they need to see the command at idle for a while, then they'll recognize a command for a higher speed. This is a safety feature, to keep that great big pair of steak knives you have mounted on the front of your plane from starting to spin if you forgot to set the throttle on your transmitter to idle before you plugged in the battery in the plane.
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wrote:

Thanks for the starting advive Tim. As for controlling speed, it's not the brake that's controlling the speed. The motor will need to spin at some determined speed but the driven wheel will sometimes be subjected braking forces and when these forces diminish the wheel must resume the determined speed smoothly. Thanks, Eric
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On Jun 23, 5:07 pm, snipped-for-privacy@whidbey.com wrote:

Just to toss an alternative out there, they are making gyros for RC planes that attach between the servo and the receiver, the gyro senses the movement and automatically moves the servo to compensate. Wouldn't quite do the same thing, but could be useful at some point.
I have a few micro planes that use pager motors for the prop, and yes, their life is not very long.
Now there is a pager-motor as plane-motor that lasts quite well, that is for a solo-pro helicopter.
http://www.rcgroups.com/forums/showthread.php?t=1326158
Dave
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snipped-for-privacy@whidbey.com wrote:

If you're getting by with pagers motors, I think these RC type motors are probalby way too big for what you need. astroflight.com does have some smaller motors these days. maxcim.com has some of the largest ones.
for precision tiny motors, check out
http://www.portescap.com/ You can't even hear some of those motors when they're running.
pancake type motors can be used AS flywheels too- try to get a motor from a DLT tape drive. they're really nice.

Maybe you can make some sort of magnetic coupling as used in pumps.
In brushless motor fans, they have what's called "locked rotor protection". If the motor stalls, the driver circuit pretty much gives up and doesn't output full power, waits a second or two and tries to start the fan again to see if the fault clears. They usually do this forever without burning out.
Some induction motors are "impedance protected" and won't burn out if stalled as their impedance is high enough that they can't draw enough power to burst into flames in the first place.
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