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DELETED (Inactive)
5 Posts |
 Posted - Dec 26 2003 : 12:55:59 AM
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Hello
I have recently bought a small Firerock Jeep Wrangler from Fisher-Price to my 18 months old son but I have found out that he got scared because of the speed of the car which is 3.5 mph. I would like to reduce the speed but I don't want to build a very complex circuit for doing so. Is there any way that I can reduce the voltage a little bit so that the car can run slower without damaging the motors or the battery? It uses two electric motors and one 6V battery.
I would realy appreciate if someone can help me find a way to do so.
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cirvin
Nobel Prize Winner
USA
1542 Posts |
Posted - Dec 26 2003 : 11:35:56 AM
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you could use a 2n3055 with a 10k pot on the base, you will ned a HUGE heat sink tho.
There is hope in the Future... |
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Aaron Cake
Administrator
Canada
6718 Posts |
Posted - Dec 26 2003 : 4:19:36 PM
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Even easier: connect the motors in series instead of parallel. Or put a high wattage resistor in series with each motor (only need a few Ohms).
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DELETED (Inactive)
5 Posts |
Posted - Dec 27 2003 : 12:04:38 AM
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Thank you both Cirvin and Aaron for your prompt answers. I guess now I have three options!!
I have a few questions. If I connect both motors in serie, the voltage is going to be reduced by half which means they might not work at all, right? I don't know why but I have seen that these cars stop working at all when the battery voltage is close to 5V. Do they have some sort of protection mechanism that prevents the motors to work at low voltages?
My second question is if I use a high wattage resistance in each motor, how can I calculate how many amperes are in the circuit? I have a multitester that can measure up to 10 amp but I think that this motors are using more than that. Would it be accurate to measure the resistance of the motor?
I went to Radio Shack today and bought the 2N3055 and the 10K pot, but I would like to test Aaron's ideas as well and see what it the best option.
One last question, is there a chance to damage the motors or the battery by doing this? I have reviewed the entire circuit and there is no a single electronic component yet I don't know what is inside the motors. I wonder why Fisher-Price doesn't include this feature (two speeds) if it is so simple to do....
Thank you guys! |
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Aaron Cake
Administrator
Canada
6718 Posts |
Posted - Dec 27 2003 : 11:21:25 AM
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quote:
I have a few questions. If I connect both motors in serie, the voltage is going to be reduced by half which means they might not work at all, right? I don't know why but I have seen that these cars stop working at all when the battery voltage is close to 5V. Do they have some sort of protection mechanism that prevents the motors to work at low voltages?
I'm not sure if there are any ptotection mechanisms. The ones I have seen are just a switch connected to a pedal. Unless the new ones use more fancy controllers. You won't damage the motors as DC motors normally run from quite a range of voltage, below and above they "official" spec.
quote:
My second question is if I use a high wattage resistance in each motor, how can I calculate how many amperes are in the circuit? I have a multitester that can measure up to 10 amp but I think that this motors are using more than that. Would it be accurate to measure the resistance of the motor?
http://www.aaroncake.net/electronics/math.htm
You can simply measure the current at the motor now, and then use the equation to find a resistance to lower the current to what you want. Be aware that you will need a BIG resistor, and it will get HOT.
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One last question, is there a chance to damage the motors or the battery by doing this? I have reviewed the entire circuit and there is no a single electronic component yet I don't know what is inside the motors. I wonder why Fisher-Price doesn't include this feature (two speeds) if it is so simple to do....
Nope, you're fine. All the Power Wheels stuff I have seen are simple brushed motors connected directly to a gearbox.
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n/a
DELETED (Inactive)
5 Posts |
Posted - Dec 27 2003 : 10:57:46 PM
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Hey Aaron, I can not thank you enough for your help and your time. I wont bother you anymore with more question but I promise I'll let you know what was the best solution once I try them....
Thank you again!!! |
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DELETED (Inactive)
5 Posts |
Posted - Jan 01 2004 : 4:39:39 PM
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Hey Aaron
First, happy New Year!!
As I promised I want to let you know that the best solution is to wire both motors in serie. It works really nice!! Now I'm going to buy a doble switch so the car will have two speeds: slow and fast (serie and parallel).
The option to use the transistor works also pretty good and it's better if you use it with a 10 ohm 1/4 watt resistor insteat of a 10k pot, however having the motors in serie is the best solution by far. Any way thank you Cirvin!!
Well, that all. Thank you both again for your help!!. And the best part is that my son now wants to drive the car and he is not scare anymore....
Ed
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cirvin
Nobel Prize Winner
USA
1542 Posts |
Posted - Jan 01 2004 : 6:24:34 PM
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Well, the pot was so you can control the speed. You could hook it to the pedal so you can have more control on the speed.
There is hope in the Future... |
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n/a
DELETED (Inactive)
5 Posts |
Posted - Jan 02 2004 : 12:09:03 AM
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You're right cirvin, however instead of using a 10k pot I would use a 100 ohm one. Over that point the motors don't even move...
I'll keep this option in mind in case I want to make another upgrade to the car in the future.
Thank you!!
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Aaron Cake
Administrator
Canada
6718 Posts |
Posted - Jan 02 2004 : 1:27:53 PM
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Very glad we could help! I always wanted one of those Power Wheels when I was a kid, but alas, never did get one...Oh well, I make up for it now. 
Anyway, if you are interested in building a variable speed controller, don't bother with a transistor/pot combination. It works by burning up excess power as heat. Very inefficient. Take a look at http://www.aaroncake.net/circuits/motorcon.htm . It's a true motor controller.
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cirvin
Nobel Prize Winner
USA
1542 Posts |
Posted - Jan 02 2004 : 2:14:45 PM
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I had one in Caifornia, but I rode the shit out of it and it eventually wore out. Then i got my go-kart. :)
There is hope in the Future... |
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Power Wheels from Fisher-Price
