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Old Mar 30, 2012, 09:33 PM
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Determining the right ESC

I'm having a hard time trying to determine what the proper ESC to use for my application is. To be fair, I sort of delved into the RC world with a decent fundamental understanding of electronics and NO experience with RC parts - I'm finding myself confused with a lot of the marketing terms/lack of actual specs.

So, the situation I'm facing is that I'm using two 180 sized brushed motors that I cannot find any specs on whatsoever - and the hobby shop assures me they are intended for 7.2V battery. Operating at maybe half throttle for less than 2 minutes, they both froze up. I assume they have been over volted, though the particular craft they were intended for uses a 7.2V battery.

Anyways, I guess the real jist of the question here is: I have these two motors, part # EFLH1210 "180MOTOR W/8T" - How would I go about finding the proper ESC to power a pair of these, given that this is not a kit sort of craft, but a scratch-built? (The ESC intended to pair with 1 motor is available, but I doubt it would handle both.). My current 30Amp ESC seems not to produce any voltage output when the input voltage is below a threshold (~4V), and I'd like to use either 3 or 6 cells (3.6/7.2V).
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Old Mar 30, 2012, 09:50 PM
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Hey now,
A ten amp brushed motor ESC would be mild overkill for these. You could prolly get away with a seven amp ESC for that matter.
Just read the instructions so you can set the correct low voltage cut off. You should be just fine with that.
Your thirty amp ESC should work too if you know how to reset the LVC. But it would be bulky and heavy too. Good luck with your project.
RobII
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Old Mar 30, 2012, 10:17 PM
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I guess im not sure about resetting the LVCs on these - The package was fairly..well it came in a stapled baggy, no instructions/etc. Maybe I need to pull it out and take a look at it, find a model #

Edit: It's an E-flite EFLA106 - Will be researching this now.
Ah, and here I see the problem - it was intended at 6V and above, and is not programable. I guess I'm wondering why I had issues with the motors freezing originally too, as this ESC should work @6V on these motors.

REF: http://www.robotmarketplace.com/prod...106_manual.pdf

It looks like realistically what I should be looking for here (for my project in general) is an ESC that's programmable; I'm quite sure this project is going to turn out changing a million times before I finalize a design.

Could you recommend a programmable ESC? Google seems to yield a lot of RC Car stuff, and I'm not sure I'm ready to start mixing and matching a car ESC into the mix here.
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Last edited by srmaddox; Mar 30, 2012 at 10:39 PM.
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Old Mar 30, 2012, 10:56 PM
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Hey now,
Personally I mostly only use Castle Creations ESCs on my models. Not the cheapest. But very programmable and amazing customer service.
Um, don't use a car type ESC on an airplane. They are limited in cell count and their battery eliminator circuit is only able to power one servo. They're also very heavy and you can't trust the numbers most companies give with them.
Good luck with the project and keep us posted.
RobII
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Old Mar 30, 2012, 11:07 PM
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Well the interesting thing here is that I've been through the instructions for this ESC just to make sure I wasn't missing anything.

While this model is not programmable, I was able to get it to power my motors on a 3.6V battery pack for a short period of time - and then it seems like the ESC is killing the power to the motor (LVC I'm guessing).

That being said, I do see that this was listed for 6-12V. I'm not comfortable running this motors continuously at much higher than 3.6V, which seems to run them at the perfect RPM for this application - the two 180's are providing primary thrust for a large bag-type blimp; the thrust/mass ratio might be off, but I'm actually quite impressed by these little motors.

I'm going to look into your recommendation for ESCs, and probably get a whole variety and kind of see where this takes me.

Right now the challenge is basically 100% scratch built (no kits), requirement is that the main pieces must all be mounted via erector set . As such, weight is one of the major issues.

As a note, looking at Castle Creations they don't appear to sell ESCs for Brush motors - am I missing something?
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Old Mar 31, 2012, 02:04 AM
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Hey now,
Um... Yeah. I guess I'm a victem of age here. They used to make them and I still have a bunch. Now that brushless motors have gotten so cheap almost nobody uses them any more. Sorry about that. Check out Tower Hobbies. They sell some cheap low end stuff but they also sell some pretty good stuff. ( go with mid range price there and it'll be fine) and they have a wide range of stuff.

I've made a few blimps in my time. They can be a real blast (um, don't use hydrogyn or it'll be a *real* blast). I used those space blanket things for the Mylar bag and sealed them with a hand held heat sealer for food storage. Worked great. I built the gondolas and frames from balsa and such though. Erector set bits would look very cool in a steam punk way, but you're right. It'd be very heavy. You'd have to go pretty big. Hmmm. Now I've got to try this... Where can I get an Erector set?
RobII
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Old Mar 31, 2012, 04:26 AM
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Actually, amazon.com sells them. They aren't quite what they used to be, but pretty close actually!

I bought the 643 piece set recently to augment my old collection from when I was a kid - was actually fairly impressed by it. I built a large, bulky frame originally to house everything before realizing that kit had a second bin of parts that had longer rails, and with some work was able to reduce the weight of the frame itself to about 4.7 lbs.

Looking at the specs for this ESC, im going to give it a go at the minimum voltage for it - 5 cells/6V NIMH.

The batteries aren't terribly heavy, but I had a local battery place wrap them. Hopefully I won't freeze these last two 180s, but If I do Ill check tower hobbies and grab some brushless ones.

One of my big difficulties using erector for most of the framing is the additional bulk of any gearing - I'd hoped to go with a cheap, replaceable motor/prop setup, directly driven and the inrunner brushless motors seem to reach just ridiculous RPMs.

At this point I'll just continue building and trying. I'd like to keep the versatility of bolting erector pieces on if I want to change it up significantly; I suppose to could fabricate some erector-compatible engine/gear housings and such.
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Old Apr 01, 2012, 09:34 PM
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As an update, I kept the e-flite 30A ESC - While it has some drawbacks, it occurred to me that I can wire the two motors in series with my 7.2V battery pack and have them operate at what I suspect is their true intended operating voltage.

I don't expect a craft like this to encounter very many situations where there is a significantly different mechanical load placed on each motor shaft, and after a few "slow-it-down-with-my-hand" tests the system recovers quite well from a motor completely stalling (although I imagine it won't take more than 30-60 seconds to freeze up the remaining motor should that occur).

So Mk. I will be series-wired on 7.2V. Currently it is functioning quite well, and I have replaced a number of pieces with balsa for easily mounting the rudder servos and reducing the weight. This has given the craft sufficient thrust on the two 180s to slide itself across a wood table with no bags for lift, so I suspect its in-air performance will be acceptable once I get the bag(s) in place.

Thank you elfwreck for your suggestions, I will be moving to brushless & Castle Creations programmable ESCs for future versions .
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Old Apr 01, 2012, 10:42 PM
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Hang on... What size props are you running on these motors? I'd be fairly willing to bet that your problems are being caused by too much current rather than too much voltage. Excess voltage will simply make the motor want to spin faster, but excess current (caused by running too big of a prop for whatever your input voltage is) will make the motor heat up inside and could cause seizing like you describe.
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Old Apr 02, 2012, 06:59 PM
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The props are little 3-blade props, 2" from hub to end of prop...Actually these motors are working fine in series with these props, I have been running them and they don't get hot at all.

Current draw was a consideration, but I wondered since these were meant for gearing down if it was just a matter of friction and too much RPM with such a low mechanical load.

EDIT: I might also add that at full 7.2V across a single motor, I did have one prop failure which I initially wrote off as a bad prop - I'm wondering if really, again, the actual RPM was just way too high (whether overvolted, underloaded, or both!)
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