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Old 25-10-2009
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Default outrunner in 1/8??

has anyone tried running a brushless outrunner in a 1/8 buggy, their revs are low ant torque very high, is there a reason for not using one??
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Old 25-10-2009
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Mounting can be a bit of an issue (depending on set-up), and they have more rotating mass than an inrunner. Also, due to the design they tend to allow for a load of dirt and debris to get into the motor, and the holes cannot be easily plugged.

There's no particular reason why they can't be used, but an inrunner is just more suited to the purpose.
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Old 26-10-2009
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could see the dirt being a problem, mounting easy enough really. was just wondering as i have a nice chunky outrunner and a hyper 7 hanging around.....
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Old 26-10-2009
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It'd probably work, you'd just need an ESC and LiPos et al.
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Old 27-10-2009
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ok sorry to kinda jack the thread but i know what an in runner motor is... i think haha... they are just like the motor which we usually run, u kno castle, tekin etc.. but what does and outboard motor look like? like one you would use on an rc car?

thanks,
-Jim
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Old 27-10-2009
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on an outrunner the can rotates around the outside of the stator rather than spinning inside it. modified my rc18b using one driving directly onto centre shaft, giving a gear ratio of 2.5:1 and calculated what kv would be needed, this works very well. i will probably experiment a bit, have an 80A heli speedo and a 12 cell pack of eastpower 4200 nimh's. will try it out when i have time, if it works i can get a proper speedo and a good capacity lipo at later date. my current lipo packs wouldnt be good enough for 1/8 i dont think, they are 3600/30c. not enough capacity or current
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Old 27-10-2009
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The capacity and the discharge rating depend on the voltage! I'm looking at running a 2500mAh 45C pack. It is 22.2V. I am also looking at running a 3500mAh 45C pack which is 14.8V. Both should give me about the same run time, and as I'm matching the kV of the motor and gearing to the voltage, they'll both do the same top speed.
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Old 29-10-2009
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i would be looking along the lines of a 4 cell pack simply to give me the ability to use it with my heli as well as the car, ie 2 birds with one stone. although i suppose 3 2 cell packs could be used with car. just dont fancy the packs being charged and balanced seperately then run together under high load. could make cells cheaper though running higher voltage and lower capacity, if they get a race saeries going i wonder what they will do about no. of cells
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Old 30-10-2009
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I'm not saying that you need to run a higher voltage, but that a couple of 7.4V 30C 3600s will be fine for testing if you already have the packs.

Higher voltages paired with a lower kV motor and appropriate gearing will be more efficient than a lower voltage with a higher kV motor geared to the same speed. This is because power = voltage * current. If the power stays the same (same top speed), and voltage increases and therefore current falls. Current causes heat build up in wires and connectors etc, (which is why connectors can cope with a huge amount of voltage, but not that much current). Additional heat causes the resistance to rise, and thus even more energy is wasted as heat. (Vicious circle).
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Old 30-10-2009
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know very well about the technical bits, i am an electrician plus been a racer for over 20 years. your 1/8 beginners guide is excellent by the way marvin, that is just what people need to do with all classes to help others get started without wasting time and money
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Old 06-11-2009
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a little question to tax your minds......
doing a little research, a 2000kv motor on 14.8volts using a gear ratio of 9.5 to 1 gives a theoretical top speed of 40mph in an eighth car. i am looking at using an outrunner i have as an experiment as you may have already gathered. motor is 470kv, 6 cell rated, 1100watt continuous, 1300watt peak for 30 secs and has some serious torque. listening to marvins excellent advice in terms of voltage so to start with will try using my 3 2s 3600 25c lipo's in series to give me 3600mah, 22.2 volt. will take up way too much space but if it works can sort proper pack out afterwards. now for the fun bit....at 22.2 volts the 470kv outrunner will need a gear ratio of 3.3 to 1, (which is attainable if you are a loony! ) to get a very similar rpm at wheels as the 2000kv on 14.8 volts. can you forsee any efficiency problems, bit worried the inrush currents to get the car moving may be a bit high, any thoughts??
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Old 06-11-2009
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There shouldn't be a problem with that. A low kV motor on a lower-than-optimum voltage would be fine. About 18S would be more appropriate!

The only thing is, as you rightly say, the amount of current required to get it moving with the correct gearing for 40 mph will be huge. The lack of voltage to get the same power output, means the current required would be massive! I doubt that your 25C 3600mAh cells will cope.

Gear it for about 15mph, and give it a go.

The other problem is that the cogging will be terrible due to the low rpm. The reason the 28k-35k rpm guide was made, was that sensorless ESCs and motors require this kind of rpm to minimise cogging.
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Old 06-11-2009
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I have run an outrunner in a 1/8 buggy before. It worked fine. It actually ran pretty good once I got the ESC set up to work well with the motor. Didnt have any issues with dirt or anything.

Here is a picture I found of the old setup. It was back in 2006 in a CEN Matrix. Not exactly a pretty setup, but back then all of the mounts and stuff were home brew. You couldnt just go buy all the 1/8 stuff like now days. It was a 2000kv Cyclon motor I ran on 5s and a Mamba Max.

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Old 06-11-2009
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Jhautz! I was wondering when some guys from RC-Monster would make it here!

The main issue with the OP's set-up is the 470kV motor, though it's good to know an outrunner will work fine in 8th off road. I suppose a buggy would be better suited, as they are more sealed from dirt than truggies.
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Old 06-11-2009
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had thought about the cogging, i think the motor i have is simply going to draw too much current to be of any use when accelerating low down due to the gearing. will have to do some saving up me thinks
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