I want to change my system from 12V to 18V, so I either need a higher voltage motor or a DC/DC converter. So, I’m considering swapping my 37D 12V motor for a 24V one, but running it at 18V. My drivers support 24V, so that’s OK.
So, my main question is how to select a comparable motor for my current 37D motor? The torque and RPM of the 24V motors seem similar to the 12V ones, so selection seems straightforward if I was going for 24V, but I’m not sure what I need for 18V.
Any thoughts or formula?
Hello.
The torque and speed of these brushed DC motors is proportional to the supply voltage. So, another option might be to continue using your 12V motor with your new 18V supply. In general, these kinds of motors can be used at voltages above their nominal voltage resulting in proportionally higher speeds and torque, but that can start negatively affecting the lifetime of the motor, and it also puts the motor at higher risk of catastrophic failure when exposed to excessive loads. However, you could avoid that by limiting the maximum duty cycle so that the average voltages applied by the driver stay in a safe range for your motors. For example, in this case, you could limit the maximum duty cycle to around 67% to keep the average applied voltage around 12V, and the motor’s performance should not change too much from what it is now.
If you decide to switch to one of our 24V motor, please keep in mind that powering motors at voltages below their nominal voltage will similarly reduce their speed and torque by a proportional amount, so you will likely need to make some trade-offs there.
- Patrick
Our current solution running at 12V (or maybe 13V with our batteries) got decently warm during ECCC last weekend, so running high is a bit disconcerting. I didn’t really think about “just” limiting it through the SMC to keep the average down, that’s worth considering, thanks for pointing that out.
Currently we “seem” to have too much torque (30:1), so there could be room to drop down to the 24V 19:1, and the higher RPM would make up for the drop from 24V to 18V - but we’d also lose even more torque. About 1/2 of our 12V 30:1 motors (if I’m reading that right). I’m not sure if we have that much headroom. And I’m not terribly sure how to calculate what we need.
Torques can be tricky to characterize. In case it helps, this “Force and torque” blog post gives some basics.
Another way you could estimate the torque is by measuring your motor’s current draw in the 12V setup. Then, you can find the corresponding torque in the motor’s performance curve from our 37D gearmotor datasheet, which you can find on the motor’s product page under the “Resources” tab.
When you make your motor selection, please make sure to consider the notes about stalling and overloading gearmotors given under the motor comparison table on page 1 of the datasheet.
- Patrick
