Hi all,
I'm messing around with a Knex motor, and was wondering if there was a more powerful version of the internal motor:
Basically, I would like to open it up, swap out the motor, and then use the whole motor + gear setup to power a project.
Does anybody know whether a stronger motor with these dimensions exist? I believe that they are size 130 DC hobby motors, 3V.
What size and shape is the motor - is it cylindrical or has it flattened sides?
How much current does it draw at 3v (volts x amps = watts) and how many watts would you like the replacement to use?
There must be a risk that a more powerful motor will damage the plastic gears.
Servos (as used in model aircraft) are a good and cheap source of small 6v motors - but it's a bit hard to know what size motor is inside. I have some servos that are about 12mmx23mm and the motor inside which has flattened sides is about 10mm x 8mm across the flats and about 12.5mm long. I have no idea how its power compares to your motor.
...R
Robin2:
What size and shape is the motor - is it cylindrical or has it flattened sides?How much current does it draw at 3v (volts x amps = watts) and how many watts would you like the replacement to use?
Just got my ruler out, its 10x15x20mm with flattened sides: http://oi44.tinypic.com/289fpfo.jpg
Well, I tried it with an extra AA and it produced more or less what I was looking for, so I was looking for one maybe around 6V, so 4 AA batteries. I didn't want to leave it on for long though, in case it damaged the motor.
I wouldn't know about the current, but at the moment it does what I need it to do fine, it's just a bit slow.
Voltage alone is no indicator of power. You need to get a multimeter and measure the current when the motor is driving a heavy load.
It's possible that the motor you have will work with a higher voltage. It's also possible that a higher voltage will damage it.
...R
Robin2:
You need to get a multimeter and measure the current when the motor is driving a heavy load.
Ah ok I see (sorry I'm pretty new to all of this!)
I measured over 500mA with no load (my multimeter doesn't go any higher), going down to around 350mA when I tried to put pressure on the motor.
Pressure presumably to speed up the motor? Motor current increases with load for a DC
motor. The no-load current is actually overcoming the frictional losses (mainly the commutator).
mikeyz54:
I measured over 500mA with no load (my multimeter doesn't go any higher), going down to around 350mA when I tried to put pressure on the motor.
Uh - how did you measure the current again? Can you show us a connection diagram or something, along with what/how you set your meter?
Most meters will measure up to 2 amps or so; many meters will go up to 10 or 15 amps (some you have to switch the positive lead to a special "high current" jack).
The way you are talking about the current dropping when you placed a load on the motor seems to indicate to me you are either measuring the current wrong and/or have the settings on your meter incorrect (either of which might lead to damage to the meter).
When a load is placed on a motor, current drawn by the motor should increase, not decrease...
cr0sh:
Uh - how did you measure the current again? Can you show us a connection diagram or something, along with what/how you set your meter?Most meters will measure up to 2 amps or so; many meters will go up to 10 or 15 amps (some you have to switch the positive lead to a special "high current" jack).
Here's a photo of my multimeter: http://oi40.tinypic.com/1t7ur6.jpg , I can't see anything over 500mA.
Basically, I have something like this:
------(M)------
| |
| |
| |
----[2xAA]-----
And then I just connected the multimeter to the motor terminals.
What is the correct way to do it? As you can likely tell, I'm not exactly great with electronics!
Wow ... a moving coil meter.
They have their uses but for most things a cheap digital multimeter is well worth the investment.
If you want to measure the voltage across the motor terminals you would place a probe on each motor terminal while the motor is connected to the battery.
If you want to measure the current flowing through the motor you must disconnect the battery from one end of the motor and connect one probe to the motor terminal and one to the free battery connection. That way the current flows through the meter as well as through the motor.
With a moving coil meter you must be sure to connect the probes the right way round as it can't measure negative volts or current (whereas a digital meter can). ALSO for the first attempt at measuring current just connect the probe briefly so that, if the current is too high and drives the meter right off its scale you can disconnect quickly before damage is done to the meter. Most digital meters have a 10 amp setting which you would use first to make sure you were not going to damage the meter when using the low current setting.
...R
Robin2:
Wow ... a moving coil meter.
Thanks for the advice! I'll try and get hold of a digital multimeter, get ahead with the times and all!
Robin2:
They have their uses but for most things a cheap digital multimeter is well worth the investment.
I quality analog meter (I'm talking something like a calibrated Simpson) is damn near worth it's weight in gold; one thing it can show which a digital meter can't (barring some expensive models) is AC "ripple" on a DC voltage. One of these days I'll have my Simpson, I swear...
Robin2:
With a moving coil meter you must be sure to connect the probes the right way round as it can't measure negative volts or current (whereas a digital meter can).
Well - not easily; if you know that the voltage will be negative, you just swap the probes around. Otherwise, you could add on a DC bias battery and/or adjust the meter centering potentiometer to put the needle in the middle of the meter for "0 volts", then you have half the range on either side for positive/negative measurement.
Robin2:
ALSO for the first attempt at measuring current just connect the probe briefly so that, if the current is too high and drives the meter right off its scale you can disconnect quickly before damage is done to the meter. Most digital meters have a 10 amp setting which you would use first to make sure you were not going to damage the meter when using the low current setting.
Actually, if you are completely unsure about the maximum of anything (current, voltage, resistance) - start with the upper range setting first, and work your way down. In the case of current, if the maximum is potentially way above even the highest current setting, then the best way to measure is to use a current shunt resistor and measure the voltage drop across it, then use Ohm's Law to calculate the current from your measurement and knowledge of the resistance (a cheap current shunt resistor can be made with a piece of thick solid core AC house wire; you can find the resistance for the gauge and length via several online tables - there's also plenty of tutorials on how to build your own shunts - but if you can afford one, a purpose built high-current shunt can be very useful; the wire they are made with is designed to not change in value under testing or temperature, but they can't be kept in continuous operation - they are only meant for testing).
Also - as a note to the OP - if you need to plug into the high-current jack of your meter, make sure to always unplug the lead and plug it back into the "standard" settings jack before measuring anything else - if you don't, and you attempt to measure a voltage, you'll damage the meter.