# Does such a DC motor exist?



## major (Apr 4, 2008)

mud_muncher said:


> Hi Everyone!
> 
> I am looking at a small, go slow project and do not want the hassle of running through a gearbox and reduction difs. I need lots of torque but a slow spinning motor. Is there a 5-10hp DC motor that runs under 300rmp prefable at around 12v. It is for a speed of around 10mph.
> 
> Thanks


Hi mud_munch,

Sure. Just get a 120 volt DC motor rated at 3000 RPM, 50 -100 HP and run it at 12V. Downside is that it may weigh 600 to 1000 pounds and be only 40 or 50% efficient at that low voltage.

Have you calculated the current at 10 HP on a 12V motor?

You have a bad idea going here  If you really need 5 to 10 HP, better look at higher voltage and gear reduction.

Regards,

major


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## jeremyjs (Sep 22, 2010)

does anyone make built in gear reduction for these bigger motors? If so that could be an option, but I've never personally seen it outside of smaller motors.


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## DavidDymaxion (Dec 1, 2008)

Golf cart rear axle?


jeremyjs said:


> does anyone make built in gear reduction for these bigger motors? If so that could be an option, but I've never personally seen it outside of smaller motors.


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## Yabert (Feb 7, 2010)

mud_muncher said:


> Is there a 5-10hp DC motor that runs under 300rmp prefable at around 12v.


300A at 12v will give roughly 3.5 hp at motor shaft.
And no small motor can sustain 300A for long time.


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## frodus (Apr 12, 2008)

mud_muncher said:


> Hi Everyone!
> 
> I am looking at a small, go slow project and do not want the hassle of running through a gearbox and reduction difs. I need lots of torque but a slow spinning motor. Is there a 5-10hp DC motor that runs under 300rmp prefable at around 12v. It is for a speed of around 10mph.
> 
> Thanks


what's it for?

you may not need that much HP, you may just need torque.


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## mud_muncher (Jun 27, 2011)

Well here is my "crazy idea"

OK, I dont have the time and money to build an electric car (atm) and I love my off roading, so i decided to build a 'hybrid' system. It would be a very small box trailer with twin motor drives something like these.

http://www.hobbyking.com/hobbycity/store/uh_viewItem.asp?idProduct=5139

It would be pulled by a very small but capable SUV (under 2500pounds). The car is self only has 75hp so an extra 15-20hp will be noticed.

The trailer will contain the batterys to run them and try to be very light (say under 600-700 pounds). The trailer will be used to give the car breif 6WD at slow speed for under about 10mins when the terrain gets tough and can be slowly recharged using an upgraded alternator on the car. This is why i wanted to keep the system light and a simple 12v alternator. I could possible use 4 batterys (48v) and a DC voltage convertor running from the car to the trailer to recharge them.

How hard is it to build a 2 stage gear reduction system? My final wheel speed is about 60rpm. 

And what sort of simple voltage control system is viable to run the motors, preffable independtly of each other so the trailer can steer?


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## frodus (Apr 12, 2008)

just use a differential and a rear axle off a truck and a forklift motor.


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## jk1981 (Nov 12, 2010)

Those motors you linked are high RPM AC motors (180kv * 12V = ~2160RPM). They need a dedicated AC controller, one capable of controlling torque at low RPM rather than shaft speed as the RC controllers normally used with them do. Maybe you know this and are looking for something similar but different?

Anyway, the bonus with AC units like that with the right controller they're your charger and drive motor all in one, no need for alternators or awkward charging arrangements, it charges as you drag it.

Gearing the motors down is a pretty small problem compared to controlling them safely and effectively, drop a motorcycle chain (or industrial duplex/triplex job) from motor to the input flange of a diff in a solid axel, you have an easy ratio selection in the range of ~1:30 up to ~30:1 depending upon the sprockets and axel chosen.

To be honest it sounds like your pusher trailer would be more of a hindrance than a help anyway most of the time. Without wishing to seem negative, would the money/time not be better spent on tyres, suspension and diff control? The trailer you propose has problems beside the electrical complexities: Too light and it'll have no traction, to heavy and it'll be a burden in normal use. Attached (pushing) too high on the jeep and you'll be losing drive at the rear axel of the jeep, too low and the trailer will have no traction. Similar deal cresting bumps and in hollows.


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## frodus (Apr 12, 2008)

Those motors are AC synchrounous, or PMAC/BLDC to be more specific.


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## HyperactiveSloth (Jun 19, 2011)

jk1981 said:


> Those motors you linked are high RPM AC motors (180kv * 12V = ~2160RPM). They need a dedicated AC controller, one capable of controlling torque at low RPM rather than shaft speed as the RC controllers normally used with them do. Maybe you know this and are looking for something similar but different?
> 
> Anyway, the bonus with AC units like that with the right controller they're your charger and drive motor all in one, no need for alternators or awkward charging arrangements, it charges as you drag it.
> 
> ...


I have to agree 100% with everything he just said.


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## mud_muncher (Jun 27, 2011)

HyperactiveSloth said:


> I have to agree 100% with everything he just said.





jk1981 said:


> Those motors you linked are high RPM AC motors (180kv * 12V = ~2160RPM). They need a dedicated AC controller, one capable of controlling torque at low RPM rather than shaft speed as the RC controllers normally used with them do. Maybe you know this and are looking for something similar but different?
> 
> Anyway, the bonus with AC units like that with the right controller they're your charger and drive motor all in one, no need for alternators or awkward charging arrangements, it charges as you drag it.
> 
> ...



Thanks for your input, you raise some great points! I have thought about the weight and the pushing issue and there are simple ways and more extreme ways to minimise this. A simple way would be to aim for a certain weight of the car say 30-40%, this way it would have similar traction. I would put a dual pivot point on the rear of the car and add off road suspension on the trailer. A more complicated way would be to fit a suspension system between the trailer and the car to slow down and resist against flexing. AN even more extreme idea is a hydrolic system to raise and lower the pivot point to adjust weights to the rear of car or too the trailer LOL. I plan to affix the trailer low on the rear bar.

The car is already very capable, it is a suzuki. It has a lift, 34inch off road tyres and twin diff locks. I just wanted to try something different that I have never seen before, and also use the trailer as a carrier on longer camping trips.

I did think of the motor bike chain idea and a duplex reduction, i do not know alot about the other idea you suggested. I was looking at 4 x 12v Lead acid batterys (some weight is actually needed on this build). 

What are AC controllers worth at 48v 7000kw, keeping in mind with the way i would like to look at building this that i need 2 of them? Is there a way you could have an electrical disconect for the motors, to stop friction when not in use? For on road use i plan to have free-wheeling hubs, but it would a pain to jump in and out of the car for every obstical.

Alot of the techincal type of off-roading i do is about getting to spots where you need a small percentage of the cars capablitys for 90% of the time. It would be great to have 3 "modes"

Easy / downhill - Motors off but system on connected and regenerating.

Meduim - Trailer along for the ride with no charging or helping.

Hard - Trailer pushing with all systems working AKA 6WD

Anyway, just spit balling ideas and i have little knowledge on electric motors hence joing up this site.

Thanks everyone again for there feed back!


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