# Geared motor questions from a beginner

#### mark84

Joined Oct 3, 2018
2
Hi,
I want a geared motor that can turn a small piece of sculpture, weighing about 6.5lbs/3kg, what I have in my head is like those cake/jewelery stands at stores that rotate, or a very slow record player.
I've figured out that a small geared motor is what I need, and I can see plenty of them available online, but I'm confused about how much they can move (the power states things like 1000gcm, does this mean it can rotate with 1000 grams on it?) and also regarding the power, must it be battery powered, I don't mind, though solar or usb would be great, but I'm a little unclear as to how to get the voltage right. As a kid I recall playing with little motors that would whizz around powered by a couple of wires from 2 AA batteries in a little holder, but if the motor is 6v then I'm not sure how to get 6v worth of power to it.
Sorry for the beginner question, I'm very grateful for any help offered.
Mark

#### Sensacell

Joined Jun 19, 2012
2,596
The weight of the object has minor relevance to the motor torque, ASSUMING the object is rotating on a vertical axis.
As long as the motor is not required to LIFT the object, only rotate it, the potential gravitational energy remains the same, so the motor theoretically does no work.

But... devil is in the details, what the motor is really driving is the bearing friction losses, so you need to overcome those.
The second problem is that a tiny efficient gear motors won't have beefy enough bearings to support a turntable.
You need to support the load with some good bearings, then couple the motor shaft to it.

The third problem is making sure you cannot destroy the motor when you accidentally turn the platform with your hand, which can produce torque levels far in excess of what a little gear motor can handle.

One simple solution is to have a small rubber idler that drives the rim of the turntable, with a small spring to press it into contact, this also acts as a clutch that will slip if you overload it.

It's actually harder than you might think to get this right.

#### MrSoftware

Joined Oct 29, 2013
1,909
This question seems to come up surprisingly often. If your goal is just to get your hands on a device, there are commercial products like this one for $30 on Amazon. It's going to be difficult to beat that yourself price wise. Thread Starter #### mark84 Joined Oct 3, 2018 2 This question seems to come up surprisingly often. If your goal is just to get your hands on a device, there are commercial products like this one for$30 on Amazon. It's going to be difficult to beat that yourself price wise.
I think you're quite right. Thanks so much for all the replies though! Much appreciated.

#### Bernard

Joined Aug 7, 2008
5,649
I like the Amazon turntable but it is 120V AC. A nice gear head motor is CAT # DCM-470, US \$ 4.75. All Electronics. USA.
Rated at 6V DC, 25 RPM. In Owl project running at 3 sec/ rev. ' Would still use a turntable with bearing, maybe a small Lazy Susan.

#### shortbus

Joined Sep 30, 2009
7,934
like the Amazon turntable but it is 120V AC
That would be a great excuse to build an inverter, like so many new members come here wanting to do.