Great New Miniature Servo

[Kazzer]

The Micro Linear Servo is a great step forward, not only for miniaturisation, but the true linear operation of the push-rod arm means less friction and wear on the push rod seals.
A small motor drives a gear meshed to a larger one which operates a worm drive sliding the push rod arm backwards and forwards.

In the photo here, the unit is placed on a US Quarter coin.


Code BT55 Linear Servo $9.00

The servo dimension: 20.8 x 12.0 x 7.0mm(whole body)
Weight: 1.8g
Torque:0.2kg.cm @3.7V
Speed: 0.12sec/60º @3.7V
Futaba J plug

[Slats]

Hi Mike,
only concern I have is the torque. Now obviously this would be used in smaller (tiny perhaps) models. Its not the corresponding surface area of the planes and rudder of small / tiny models that cause me concern, its whether or not the standard 1/16" WT seals are going to load it up too much.
David and others what do you think?

Mike, can you please let me know what the servo motors dimensions are in terms of length of the motor case and outside diameter?

Thanks
J

[He Who Shall Not Be Named]

Hi Mike,
only concern I have is the torque. Now obviously this would be used in smaller (tiny perhaps) models. Its not the corresponding surface area of the planes and rudder of small / tiny models that cause me concern, its whether or not the standard 1/16" WT seals are going to load it up too much.
David and others what do you think?

Mike, can you please let me know what the servo motors dimensions are in terms of length of the motor case and outside diameter?

Thanks
J

John,

Mike and I talked it over about these little things. I think their described as 'microb-servos'. I'm convinced that the only way to utilize them correctly is to magnetically couple the output arm to an external pushrod, like what you see illustrated below using the little blue mini-servos sold by Mike. This particular SubDriver is 1.25" in diameter and fits the old Aurora/Revell 1/230 SKIPJACK kit. Things would be a whole lot less crowded in there if I had the microbe-servos back then!



We agree, John, that the standard watertight seal would present too much resistance to the low torque of the little servo, hence the need to go the magnet route.

Below are some close-ups of the 'servo box' I came up with that interfaces two lengths of 1.25" o.d. Lexan cylinder. Pictured are the mini-servos. I could cram twice as many microbemicrobe-servos in there with room in the bottom of the servo box for more devices.

The last pictures shows how to mechanically link two servos so you can work an X-tail without electronic mixing. Hello Revell 1/144 Type-212!



David,

[Slats]

Thanks David, that is a nice piece of innovation.
J

[Subculture]

For their size and weight these are torquey little servos, as they're based on a jack screw. But they're no match for the 2.5-3 gram servos. These are really designed for very small indoor flyers where weight is paramount and the loss of a couple of grams can mean an AUW reduction of 10%.

Also bear in mind that these are designed to run from a single lithium cell- hence the 3.7v operating voltage. If you try and run these from a 5 volt receiver buss you'll let the magic smoke out of them.

[Outrider]

When I look at the servos for underwater use, I think of the 1:72 Fine Molds Ko-hyoteki (Target Type A) submarines. I think that it's unlikely that we'll ever see a D&E sub driver made that small, but I'd love to see that little beast (the Target Type A) in the water with other 1:72 subs. I'm just back from Pearl Harbor and have studied up on the Japanese use of small subs in the 1941 attack. Two of the five small subs made it in to the harbor and fired weapons. One of these was sunk after weapons release, but another seems to have hit the Oklahoma and then made it to a safe location in the West Loch and scuttled. The Ko-hyoteki crews must've had some very big cajones to have entered Pearl Harbor with only one very constrained way in or out.

Back to the point of the thread, if we ever see that 1:72 Fine Molds kit as an RC, it will likely use these servos.

As a bonus, David teases us again with the Revell Type 212! But at least we know it's still "on the list" and, happily it's still available from Revell. The D&E 1:96 GRP Type 212 will probably prove more durable in the long run, but the polystyrene kit is probably going to be easier for most mere mortals to assemble.

[He Who Shall Not Be Named]

As is your Type-214, Jim ... still in the rotation, I assure you.

David,

[Slats]

Getting back to my other question Mike, can you please give me some measurements on the motor itself (Diameter and case length)?

I have a small job that I could cannibalise the motor for.

Thanks
J

[Kazzer]

If you try and run these from a 5 volt receiver buss you'll let the magic smoke out of them.

The manufacturer says they'll operate to 5 volts. Samples en route to The Cave for testing!

[Subculture]

Hmmmm. I would suspect the control circuitry could take it, as it should be regulated probably to 3 or 3.3 volts. The motor will be a different kettle of fish however. Those motors are pager motors, used for the vibrating mode on mobiles etc.

They're designed to run on a single lithium battery, which is 4.2 volts max. Start running them at 5 volts and I think it will shorten the lifespan.

[He Who Shall Not Be Named]

The manufacturer says they'll operate to 5 volts. Samples en route to The Cave for testing!

Thank God! You scared me there for awhile, Andy.

Don't want to have to make a special voltage dropping circuit to cram in there just to protect the servos from the receiver bus voltage.

I do appreciate the heads-up thinking on that issue though.

You're right, of course: those things were initially designed for ultra-light, small, aircraft employing a single-cell battery and might indeed have not been beefed up to take the full range of receiver operating voltages -- good thing the manufacturer made these things so versatile in that department. If Mike and I had plowed ahead without considering that (which was exactly what was happening till your above post), and if the servo could not dine on a normal receiver bus voltage without frying, then we would have wound up pouring Mikes money down a rat-hole and wasting my very valuable time.

Good thinking, Andy. Your input is always appreciated ... helps keep me honest and on my toes, and Mike out of the poor-house.

David,

[Subculture]

A simple method to drop the voltage (if this proves to be a problem) would be to wire in a 4001 diode inline with the positive power wire. This should drop the voltage by about 0.7v and bring the 5 volt very close to single cell lipo voltage.

[Kazzer]

I contacted Aroosh at Sombra Labs regarding this potential problem and here are his commentrs.

The operating voltage range should be fine, after all the servo bus on the SL-8 just re-supplies the battery voltage to the connected devices. As long as this new receiver conforms to the industry standard PWM input, it should work fine. If you're concerned, get one sample to test out before ordering a large quantity. I've actually never received a word regarding issues with servos with our receivers.

Regards,

Aroosh Elahi
Sombra Labs Inc.

[He Who Shall Not Be Named]

A simple method to drop the voltage (if this proves to be a problem) would be to wire in a 4001 diode inline with the positive power wire. This should drop the voltage by about 0.7v and bring the 5 volt very close to single cell lipo voltage.

We talking a Zener type diode here, Andy?

David,

[Subculture]

No it's a normal rectifier diode. Have a read of this-

http://www.kpsec.freeuk.com/components/diode.htm