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08-19-2005, 12:07 PM | #1 |
RCC Addict Join Date: Mar 2005 Location: Saginaw
Posts: 1,721
| Using Mulitiple ESCs and Larger Motors
I am getting back into building my cutsom rig, and I have a few questions. I want to use a large gear motor, but it is not a "hobby" grade motor. I am not worried about weight issues, or driveline strength, or center of gravity and stuff like that. What I am not too sure about is the electronics aspect of it. I will give the specs of the motor sop you know what I am working with: 162 RPM @ 12 VDC 1.5 Amps - No Load Rating I know a bit about electronics, but I am not too good with conversions and equations. Is it possible to use a "hobby" esc for this motor? Also, if I wanted to use two motors, or maybe 3, could I use a seperate ESC for each and tie them all into one RX? I would be using a seperate battery pack for each motor/ESC combo. Also, would a standard battery pack be able to run one of these motors? I realise this motor is rated for 12V, but I may be able to run it at a lower voltage, with lower rpms. I am just wondering if it can put out enough "juice" to run the motor. I know this is a far-fetched plan, but it is something I have been wanting to try for a while now, just for fun. Any input is welcome, thanks. Last edited by Mad Scientist; 08-19-2005 at 12:13 PM. |
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08-19-2005, 02:04 PM | #2 |
Pebble Pounder Join Date: Nov 2004 Location: P-Town!
Posts: 119
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I fit really pulls 1.5 amps, you should have no problem. But I would try to find the stall amps and make sure they don't exceed the limits of your chosen esc. But you should be fine, some motors we use pull 50 amps.
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08-19-2005, 04:10 PM | #3 |
RCC Addict Join Date: Mar 2005 Location: Saginaw
Posts: 1,721
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Yeah, I'll try and find a spec sheet for more details, all it says is that the no-load rating is 1.5 amps. I wasn't sure what kinda of draw "typical" rc motors have, so I just wanted some input before I go ahead and buy everything. What about using multiple ESCs on one RX? |
08-19-2005, 08:04 PM | #4 |
Pebble Pounder Join Date: Nov 2004 Location: P-Town!
Posts: 119
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Assuming you set them up the same, I wouldn't see a problem with it.
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08-19-2005, 08:46 PM | #5 |
2006 2.2 National Champ Join Date: Dec 2004 Location: Big Bear Lake
Posts: 8,328
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Moved to Electronics.
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08-20-2005, 02:26 AM | #6 |
Quarry Creeper Join Date: Nov 2004 Location: MANVILLE
Posts: 413
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with 162 rpm at 12 volts will be really really slow.probably be way better to use a tipical hobby motor with a gear reduction.with such low rpm's can't imagine having much torque
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08-20-2005, 09:52 AM | #7 |
Newbie Join Date: Mar 2005 Location: Cincinnati
Posts: 21
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I have an 18v motor and gearbox from a Milwaukee cordless drill in my newest rig. I run it with a standard 7.2v pack and a Tamya 302bk $50 esc. Never overheated the esc and tons of torqe and 2 speeds to boot. Top speed in high is a little slower than I walk.
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08-21-2005, 11:33 PM | #8 | ||
Newbie Join Date: Aug 2005 Location: over yonder
Posts: 18
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the only thing i would be worried about is how damn slow you want this crawler to be. with typical reduction gears, you are looking at 4-10 rpm at the wheels. that is around 6.5-16 feet per minute. of course you could maybe gear it higher with a total reduction of 2:1 or so, but then you have to wonder if your motor is strong enough for that kind of gearing, which i just now figured out is what SPEED_RACER was probably talking about. and if you run a 7.2 volt battery pack, that will equate to less power also. the only thing i can think of this working is that this is a very large motor that draws a ton of amps under load. Quote:
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08-22-2005, 06:07 AM | #9 | ||
Newbie Join Date: Jul 2005 Location: Richardson
Posts: 18
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08-22-2005, 04:47 PM | #10 | ||
Newbie Join Date: Aug 2005 Location: over yonder
Posts: 18
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also, everything has almost no torque at no load because a load is required to measure torque. Quote:
A = amperage, R = resistance, V = voltage in an electric motor at room temperature, the resistance is very low, leading you to belive that it would draw high amperage from 14.4 volts. and it will, for a split second. as soon as that high amperage runs through the motor and is acted apon by the magnets, the motor wire heats up creating a higher resistance. so the motor goes from less than .1 ohm to .3-1.5 ohms or more in less than a second. the smaller the motor is, the less heat it will generate but also the less heat it can withstand before it frys. and high amperage is what creates heat. a vacuum motor while running has a pretty constant resistance of around 2.5 ohms. if we use our formula, AxR=V we come up with Ax2.5=115 so A=46. if we use the same formula on a typical hobby type motor in an e-maxx and we assume it is a high quality one whose resistance never gets over 1 ohm, Ax1=14.4 that means A=14.4 and in an e-maxx that is 2 motors so a total draw of 28.8 amps. and usually the resistance would be higher so the amp draw would be lower. now you say that you use cordless drill motors in your e-maxx? well the resistance in those motors would be even higher than in a typical hobby motor so if you are still using 14.4v then you are actually drawing less amperage. also, another way to figure this out is that if you are using 3000mah batteries, you can only draw a total of 6amps for an hour. that also comes out to 12amps for 30 minutes, 24amps for around 15 minutes (<--my e-maxx average run time) 50 amps for less than 7 minutes (by now electronics are frying and high resistance created by heat causes more draw so less run time, at 50 amps most of your circuits are toast.) if you run 100 amps, your run time would be less than 3 minutes but in actuallity you wouldn't even get that because your esc and batteries would boil out of the truck. i do know what i am talking about because i went to school at UTI, and aced all of the electronics classes. it's not voltage that frys electronics, it is amperage. it's just that increasing voltage also increases amperage. | ||
08-22-2005, 05:58 PM | #11 |
Newbie Join Date: Jul 2005 Location: Richardson
Posts: 18
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Kt = T / I or T = Kt*I Motors draw their highest current at stall (initial start-up). So using the formula above, when is peak torque? You are correct in saying they have constant torque IF the current is constant. In RC there is hardly ever constant current. Where did I say that the drill motors ran at 100A for 3 minutes straight? They had peak draw of around 120A. (That was documented by onboard data collection). They usually ran around 20A during race conditions. You're not the only person that went to school |
08-23-2005, 03:35 AM | #12 | ||
Newbie Join Date: Aug 2005 Location: over yonder
Posts: 18
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ok, you didn't say that you were drawing 100 amps for 3 minutes but you also did not say that you were drawing 100 amps peak at start up. what you said was "I ran Dewalt motors in my E-maxx and was drawing over 100A." that sentence lead me to misunderstand you. i still don't believe you were drawing that much though even for start up, unless for some reason during that particular start, your truck was under unusually high load. but this initial "high" draw is what i was talking about in my last post. you are also correct in pointing out that torque is constant at a constant current, and this is where my inexperience with rock-crawling comes through. i am used to drag-racing and oval track racing where the current is actually constant (full throttle the whole time) i didn't even think of varying current... my bad. and finally, i made a typo in a previous post that might have lead to some confusion. i said: Quote:
"applying more voltage only increases speed and therefore horsepower (up to a certain rpm) while the torque curve stays constant." and by that i meant that the rate at which torque rises or falls is constant in relation to the current, creating a line instead of a curve on a graph. um... | ||
08-23-2005, 05:54 AM | #13 | |
Newbie Join Date: Jul 2005 Location: Richardson
Posts: 18
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We're all still learning. Your previous experience with oval and drag is a bit different than offroad racing or rockcrawling. I can see where you're coming from now. The ol' E did draw over 100A. Not for extended periods of time, but it did. Multiple trips of a 100A circuit breaker and the onboard data collection proves it. You're right though it did happen at start-up (read full throttle wheelies) or any kind of major direction change (it's tough getting 13lbs worth of stuff moving in another direction other than what's going). It was definitely unusual. Quote:
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08-23-2005, 12:04 PM | #14 |
Rock Crawler Join Date: Aug 2004 Location: woods cross utah
Posts: 523
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how does a vacuum motor draw 46 amps when most household breakers are 15-20 amps?
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08-23-2005, 06:19 PM | #15 | |
Newbie Join Date: Aug 2005 Location: over yonder
Posts: 18
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i would say that the average variety vacuum motor would run at 18-25 amps. a lot of people do in fact trip their circuit breakers when vacuuming. (my grandmother does this a lot) i just checked and all of the breakers in my house are 25 and 30 amp, except for the laundry room and stove/oven breaker. my house was built in 1967 so it's not like all the wiring is new or anything either. i remember before we put in the circuit breakers we had an old fuse box and the 15 amp fuse would bust every time i vacuumed. | |
08-23-2005, 07:13 PM | #16 | |
06 Super National Champ Join Date: Jun 2004 Location: Stark Industries Bar and Grill
Posts: 11,361
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...at zero RPM. http://www.gizmology.net/motors.htm | |
08-24-2005, 03:15 AM | #17 | |
Newbie Join Date: Aug 2005 Location: over yonder
Posts: 18
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yes, zero would be the lowest possible rpm wouldn't it? | |
08-24-2005, 04:28 AM | #18 |
06 Super National Champ Join Date: Jun 2004 Location: Stark Industries Bar and Grill
Posts: 11,361
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Yup...it's called stall torque.
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