Choosing gear ratio: 75rpm @ 46Nm vs 100 rpm @ 37 Nm

I am starting to dive into 6 dof topic, among other things trying to make a list of needed hardware.

Geared DC motors seem to be optimal for a reasonably priced homebuilt system, so that decision is already made. Having read a number of discussions on this forum, I understand that torque of >20-25 Nm should be sufficient for 6 dof, especially if gas struts are used to help supporting platform weight.

One of the candidates that I am considering is Transtecno’s EC350.240 with either 30x or 40x gearbox. The first option gives 100rpm and 37Nm, the second – 75rpm with 46 Nm.

Do these look as viable options? What would be the better choice for primarily driving simulator? Should I aim for higher torque or higher rpm?

Thanks!

Regards,
Grigory

From your explanation they do seem strong enough. Do you have a link to the motors or a spec sheet?

Thanks!

Sorry, that's my first post and the system does not allow me to post links.
The spec sheet for the motor is on transtecno's website: www_transtecno_com/ru/products-ru/pdf/198id-Transtecno-DC-Gearmotors-catalogue-ALU-DC-0915.pdf

I am considering EC350.240 motor with 350/040 gearbox at i=30 or i=40 ratio.

The thing to remember is that you're using these motors to provide linear motion via (usually) a control arm. That control arm converts that torque and rotational speed into a linear force and velocity. The length of that control arm determines how that rotational energy is converted to linear. A longer arm will give faster movements (and a larger range of motion), at the expense of reduced force, a shorter arm reverses that, so you can really achieve the same results with either, just by varying the length of your control arm. The significant difference being that a longer arm (requiring more torque, and less speed) will give you a greater range of motion.. but also take up more space.

You're sweeping out an arc from the gearbox shaft to the connecting rod attachment point. If you draw a straight line between start and end point, you get an isosceles triangle out of it (for a 60 degree rotation, an equilateral = easier math!) So a control arm of eg 10cm length sweeping across 60 degrees will push 10cm. Lengthen that arm and it doesn't have to turn as far to push that same distance, so it can do so a little slower... but it needs more force to do so.

IE: the control arm is part of your gearing in itself.



I'm a little concerned about those figures though. It's the same motor driving them, so the input power is the same. The 100 vs 75 RPM motor is a 4:3 speed ratio, so all else being equal the torque should be in a 3:4 ratio, meaning the 75PRM box should be putting out 49 (and a third)Nm, or the 100 is only doing 34.5. Either their figures are wrong or that 75RPM box is significantly less efficient than the 100. My money would be on the former.

Thanks! I actually purchsed the 100rpm gearboxes, mostly because the 75rpm ones have some strange "service factor" of 0.7 with supplier's comment that gearboxes with SF of less than 0.8 are not covered by waranty and are not recommended for use.

I am planning to use these with 15cm levers and three supporting 350N gas springs. Simulation shows that this may produce about 1g of acceleration both up and down for a 100-110 kg platform.