Help with my brainstorm

Hi everyone,

I have an idea for a new gizmo that I'm trying to make a working model of. It will use a 12volt electric motor and want to spend as little as possible on it until I'm pretty sure it will work, so I'm going to scavenge for parts when I can. The most expensive parts that will go into it is the electric motor and the battery and I have a few questions:

1- Does an electric motor draw whatever power it needs or is the power forced into it?
2- If it draws what it needs, can I take a 12volt motor and use an 18v battery with it without problems? So if I scavenge an electric motor from a 12v battery powered drill can I run it with an 18v lithium battery?
3- What about the amps? If I use a 12v motor that normally runs off a 12v car battery, can I run it with an 18v lithium battery that has less amps?
4- Any other specs I need to focus on?
5- When I find the right electric motor, which I think will be a small 12v gearmotor, where should I go to find a low cost supplier?

I'll have more questions later but if you could help me with this I can get started. Thank you!


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Bretina (author) 4 years ago
Hey guys,

I hope you've all been well. This project hasn't been easy but I'm making some good progress and at least have the lifting thing pretty much figured out. Now I'm stuck again with finding the right motor.

I found a source for electric motors but they are all unmarked except for the occasional voltage stamp and I think 12v is what I want. How can the other specs, such as amps, torque, rpm or even voltage be determined on these unmarked electric motors? Is there a machine to connect them to which tells the specs or are there shops that specialize in this? Also, I have a multimeter and will get a benchtop power source if this is typically done with these tools. If so, how? I need to know the specs of a used one that works for me so I can source for new ones later.

Thanks again,
Bretina (author) 5 years ago
Thanks Josehf. I had considered something like that just to get it to work and maybe workout the size it would eventually be. But in the end, I think new and dedicated parts would be needed if I ever wanted to interest others to buy it. I'll probably give it a try anyway if only to learn and apply the suggestions you guys have helped me with.

Who knows, maybe this will only be an exercise but with what I learn it could lead to an even better idea :-)
You know what might be an idea look for battery powered drills in garage sales second hand stores and the garbage.
Use an ordinary threaded rod and nut from a hard ware store in place of the drill chuck.

Bretina (author) 5 years ago
Ok steve, I'll remember that about the rating. Cycle? I'd say normal use would be one up-down cycle every few days or so at the most.

Also 12 volts to keep this as simple and low cost as possible but not with a car battery. It needs to be much smaller, like a LiOn power tool battery. My brother has a DeWalt power screwdriver and it seems to have a lot of torque. I checked their site and it's about 70 lbs. From the feel of it it feels like it should be about enough to turn the lead screw and a 400 lb load, but I'm not sure. I thought to get their replacement motor but it's not self encased and the screwdriver housing is its case, plus it's too expensive at over $60.

I'm beginning to think this may not be possible, especially if I want to keep the cost low - like no more than $25. :(
I think that's a bit unlikely. How far are you moving the load again ? If you can do it slower, there are big satellite dish actuators that can shift that kind of load.
Bretina (author) 5 years ago
Thanks again. I think I now have a foundation of min/max parameters to at least eliminate some dead ends.

Here are a couple resources I found which may help others here:
101 level info on lead screws when you register, then you also get more info. from MIT on gears, etc.:

You guys have really helped me on this. It looks like I'm going to have to buy a motor and a 12volt one should be best to keep things as simple as possible now. As for the battery, I think I need to focus on that the amps in the battery are at least what the motor is rated at. Correct? Or, is it the watts? If it's the watts, none of the motors show that spec. Here's a motor (as an example) that would fit:
How do I match the right LiOn battery for it - will 18v safely work with a 12v motor with the resistor previously mentioned or would it be best to stick with 12v if at all possible?
DON'T use a resistor to control the speed.....

The motors you flag are nowhere NEAR powerful enough to meet your spec.

What you need to work off is the RPM you need, and the torque you need. Make sure that torque is the RATED and NOT stall torque

What kind of duty cycle is this thing running ? Is it permanently driving up and down, or once every hour or what ?

A decent battery will supply much more than your motor can handle. A car battery, which is 12V can supply easily in excess of 1000A.....just not for very long....
Bretina (author) 5 years ago
Thanks boys! The motors around the house are too big. I might call a local electric motor rebuilder, like Josehf, but I have a feeling they will just have industrial size motors. I think my best bet is to search for one with Steve's specs.

I searched for the 5/8" ACME lead screw and I found they are used for scissor jacks and the like, which lift 4000 lbs. or more! Isn't that 10 x more lead screw strength than what I need? The lighter and less expensive my device is the better. What would be a smaller but sufficient lead screw diameter for my measly 400 lbs.- 3/8"?
Depends on how you're loading the screw, what its made of, and how safe its to be. I wouldn't design for anything less than 150% of your rated load, so nothing smaller than 7/16" in steel, and with bronze lift nuts, not plastic. If you use plastic nuts, then my 5/8 is still the correct size.
I use to rebuild electric motors equipment would come from Europe with motors rated differently than North America and we had to test for or rewire the motors to work here.

To do this we had a variable power supply.

We started at the rated voltage and cycles and adjusted the voltage and cycles up until we reached the desired voltage and cycles all the time checking the current with a meter.

If the current went down and then up or if the current just went up we rewired the motor.

Now on AC motors the rpms will change with the cycles and if the rpms changed too much for a pulley wheel size to compensate for we rewired the motor.

As long as the current went down and not up we certified the motor safe for North American standards.

Take the 12 volt motor and connect it to a variable power supply and slowly turn up the voltage from 12 volts to 18 volts all the time checking the current with a meter.

As long as the current goes down and not up it should be safe for 18 volts.

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