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Thread: Motor Swap


  1. #1

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    Motor Swap

    Hi guys,

    Well I have redesigned my project, here is my previous posthttp://www.rcuniverse.com/forum/m_9489456/tm.htmI have taken the gears out of the RC car and installed them onto an aluminum arm, I am also going to use a O-ring as the belt and also as the tire. The whole wheel/bearing assembly as it stands weighs 1.13lbs. here are some photos to help describe what i'm workingon





    The current motor from my RC car is a RC-280SA-2675, I couldn't find anything on it but i came close with the RC-280SA-2865 which can be found herehttp://www.mabuchi-motor.co.jp/en_US...s/rc_280sa.pdfI have calculated the motor to output 1.68W, I guess my question is do you guys think it will be powerful enough to move this thing? The whole thing as it sits right now weighs about 4.27lbs if this engine is not powerful enough could i use a different motor that operates on 9.6V? In other words I know i would need a speed controller and the motoritselfbut could i just cut the wires to the old motor and swap in the new one and it should beOK? I am new to this and am seeking help from the pros!

    Thanks guys!

  2. #2

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    RE: Motor Swap

    Also could i increase battery power with out burning the motor?

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    iron eagel's Avatar
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    RE: Motor Swap

    No you'd cook the motor.
    You would need more than a 2 watt motor to move this car, to give you an idea of power required...
    750 watts = 1 hp

    I think you should be looking at a brushless motor and ESC combo that runs on 18.4 volts and can carry a lot of watts.
    Ask in the car & truck forums they would have a better idea of wattage needed.

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    RE: Motor Swap

    Well I the car weighed closer to 5lbs before I stripped it down, I still have more room to go in shedding weight if possible.

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    iron eagel's Avatar
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    RE: Motor Swap

    Reducing the mass(weight) of any vehicle be it car/truck, watercraft, or aircraft will improve it performance and handling.
    As far as a vehicle the improvements are ranked in this order:
    Lowering the β€œun-sprung weight” such as reducing the weight of: tires, wheels, differential, steering gear, suspension components, will have a dramatic effect.
    Reducing the weight of the chassis, power plant/engine, and fuel/battery load.
    Reducing the weight of the body.

    Keeping in mind the following constraints as you proceed: you must try to keep the center of gravity as low as possible, as well as centered to the wheels front to rear and side to side.

    I have a question regarding your power figures.
    You said you figured it out to be around two watts?
    That would mean a current of 1 amp at 2wo volts (roughly) using the P=I*E formula.
    P=two watts
    I= one amp
    E= two volts

    Or other values would be:
    Β½ amp at 4volts= 2 watts
    ΒΌ amp at 8volts=2 watts

    Does this agree with how you got your two watt figure?

    Why I ask is this that means you are imputing 2 watts into a brushless motor or 0.0026hp (1/375hp). With a brushed motor such as you are using because of it inefficiency you are only getting around 0.001 hp (1/750hp) of actual torque power out of the motor, A brushless motor is roughly 90% efficient as compared to a brushed motor that runs around 50% because of mechanical drag and electrical loss due to the brushes. I doubt that you’d get anywhere the type of performance out of your setup for all the work you have put into it using the motor you mentioned, half the power from you battery is just going up is smoke. At least with a brushless motor you get a 40% increase of power right out of the gate. You could use a simple of a substitute as a brushless replacement for a speed 300/400 motor type or if you wanted to really pick thing up a motor such as a ducted fan motor could be entertaining. Either an ElectriFly Ammo 25-56-3200kv or A HET (High End Technology) typhoon 2W-23 which are 28 mm diameter motors around two inches long may work for you. You can check for other sizes/ power on either off their websites. The KV rating is the RPM/volt output for example: a 3200 kv motor will spin at 6400 rpm at two volts (no load). The down side is you have to change your speed controller, and perhaps your receiver if the speed controller is built in, not a real big deal.
    You could google some cheap sources for parts…
    Bp Hobbies, hobby King Turnigy are a few thoughts.

    For what it worth…
    For a 5 lb airplane if I go electric I use 7500-1500 watts or 1-2 hp motors to power them, I not sure how that compares to the cars.

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    RE: Motor Swap

    ^ well I hooked the motor up to dc power supply and the battery pack says 9.6V so I ran the motor at 9.6V and it was producing .27A P=V*I, but then I found the spec sheet above and used the motor  closest to mine and it states it runs on 6V so i repeated the process and thats how i got my 2W. I am using a Nicco Transform truck http://www.rcmania.com/reviews/nikko...tor-car-truck/ its pretty much this thing but maybe 9 or 10 years old and its red. I left the transforming part in car because of having weight in the center but i could remove it to shave some weight. It basicly has a motor in the center with an axle and it folds the chassis in half. I figured if the current motor could propel this thing, which was almost 5lbs and is now closer to 4lbs -> 4.21lbs to be exact. Im new to the modifying of RC cars so I am not sure if the speed control is integrated or not. I would imagine and airplane would have to over come more forces the a car. Basicly I just want the thing to move, so it has to have enough torque to overcome friction and turn the pulleys, it doesnt have to go fast, but it would be cool if it did I am going to look into those motors. As far as gearing goes, could I get a motor gear that would work with the current gears I have or could i get gears elsewhere? 

    thanks for all your help guys.

  7. #7
    iron eagel's Avatar
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    RE: Motor Swap

    With the gearing you have your power levels do not have to be anywhere near the specs of the two motors I mentioned, your right with an airplane you are dealing with direct drive to the loads for most part so the power requirements are much higher. I threw out those two motors because they are physically about the same size and weight as the one you are using. Unfortunately I don't have any experience with RC cars/trucks so I have little knowledge about the setups, however I do know of the advantages of brushless over a brushed motor makes it worth the effort to swap the brushed motor for a brushless were you gain 40% efficiency right out of the gate. You should have little problem finding a good substitute that will fit and work in your application. Where the power requirements are so low in your application you will find a lot of possibilities, go with the highest KV rating you can find and that will give you some real performance. For example a HiMax 5300KV may be a good choice, at 9.6 volts it will spin up to almost 51,000 rpm, if you know your gear ratio and tire sizes you could calculate your possible top speed from that. I would imagine your current gearing would work very well with any brushless motor that you could physically mount in this setup no problem at all and both your speed and duration on a charge would go up by quite a bit. All you need do to fit your current gear setup is use a motor with the right shaft size I would hazard a guess that you need a 3.2 mm shaft.
    Depending where in MA you are located I can give you some local hobby shops that could give you some advice about you car. There is one in Hanson which has a lot of car parts and a good selection of motors and controllers in stock as well as knowledge about swapping out brushed motors for brushless.

    For what it is worth I have run a brushed motor such as you have with a 3 cell (11.4 volt) li-pol battery with little ill effects for a year or so at this point but I doubt the brushes are going to last much longer...
    Keep in mind that when using li-pol or lithium ion batteries, they require special chargers and will not work with with normal batter chargers.

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    RE: Motor Swap

    thanks man, I'm located in Fall River, Ma and also Boston, ma (home and school) I know of a Tower Hobbies near my home but none in Boston. Im guessing i would get a lot of knowledge there as well. Thanks for all your help

  9. #9
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    RE: Motor Swap

    Tower may or may not be able to help you...
    Hanson Hobby is on Rt 27 in Hanson, roughly 15-20 minutes east off of Rt 24 from the exit in Brockton. They have a website where you can get the hours they are open most night till 8Pm except Wednesday they close at 6 pm.
    Another place you may want to check put is CME hobbies in Plymouth (while they do mostly helicopters) they have a good selection of electric motors.
    You may also want to check out a store in New Bedford I believe it is called "Big Boys Toys".
    There is also a hobby store done in Hyanis near Macy's although they don't have a big selection of motors and controllers.
    One place that does have a good selection of electrics is RC buyers Warehouse in Nashua about 1/2 north of Boston on rt3.

    What you are doing should not be all that much of a big deal as far as a motor swap.
    If you have had the car open look and follow the leads back to the ESC from the motor.
    Is it part of the receiver or a separate component?
    If it is not an integral unit with the receiver all you should have to do is swap out the ESC, if it is you will have to swap out the receiver as well.
    If you have any background in electronics you could probably get even more creative...


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