My 3 DOF with heave

Hello
Great project Sebastian2
Is it a good idea to use 48V motors?
Do higher voltage motors need lower currents on the regulators?
Will they work properly?
Best regards
Tadek

So you have 48v regulators? So why not. I think the psu will get more and more expensive? Maybe at some point you get fried if the rig has a malfunction and a Short to ground or you

Yeah, I think 48V PSUs, drivers/regulators and motors will be harder to find (and more expensive?) than if you used 24V (or 12V).

If you manage to find some and run into trouble, you are much less likeley to find support by users that have experience with the parts you use (or similar ones).

So what are the advantages of 48V? You can run cables with a smaller diameter. Can't think of much else. This might make setting up the wires a little easier. But the type of insulation on the wire also affects that (silicone insulated cable is much easier to bend than regular cables).

All in all, the risk/reward balance for 48V doesn't seem good to me. If you stay in the range of roughly 250...750W per motor, 24V makes much more sense (in my opinion).

Thanks for the tip

I was guided by a smaller current and therefore smaller problems with reverse currents

Sebastian2 your project is perfect for me.
Do you have a recorded video of the platform in action?

Would you be so kind as to share the electrical diagram?

Best regards
Tadek

Thank you. Check page 3 of this thread for a wiring diagram. A video of the moving rig can be found on page 4. The wiring diagram for my "soft off" implementation can be also found on page 4.

Ah I see. It's more like regenerative energy that's the problem. Your rig is moving and you want it to suddenly stop. The energy has to go somewhere, it's as simple as that.
So even if you have half the regenerarive current, you have twice the regenerative voltage.
I'm quite sure that a 48V motor will generate about twice the voltage of a 24V motor (with all else being equal). So If you don't take measures to handle regenerative energy you still will trigger your PSUs over voltage protection.

Yes
Hi
But I decided that safety is the most important thing.
24V is the best.
Direct current is no joke.

I have a question about DC regulators

Why did you choose Cytron MD30C?

I know that the price is good.

It is known that a large regulator current is the basis.

Does the PWM frequency affect the smoothness and quiet operation?

Until now I have used cheap

BTS7960B

they have supposedly ?/43A

but frq 25 kHz
a
Cytron MD30C
30/80A
frq-l PWM frequency up to 20KHz (Actual output frequency is same as input frequency when external PWM is selected)

moust Cytron MD30C is without radiator

I chose Cytron drivers because It felt like it was a good compromise between price and quality. I didn't want to spend the money on Sabertooth 2x32 but I have read sooo many threads where people had issues caused by cheap chinese H-bridges that suddenly stopped working or were faulty from the start. I did not want that.

I chose the MD30C model because my 500W 24V motors had a nominal current draw of 500/24=20 A. I wanted some head room, so a 20 A driver was out of the question.

In principal, PWM frequency affects acoustics. I learned that the hard way. At first I controlled my 3 motors by a single arduino running SMC3. Because of limitations of the arduino board, the third motor can only be controlled using 4 kHz PWM frequency. This caused a high pitched sound everytime the third motor was turning, which was very annoying. With motor 1 and 2 you can choose the PWM frequency via SMC3utils, with options like 30, 25, 20... kHz (there are more, lower values available, too). But with motor 3 you are stuck at 4 kHz. That's why I added a second arduino. Now I can control all 3 motors using 20 kHz PWM. I chose that setting because it's the maximum for my cytron MD30C drivers.

I'm pretty convinced that you won't hear 20 kHz. So 20 kHz is as good as 25 kHz.
You can test it by trying an online freuqncy generator to find out the max frequency you can hear. If you are older than, like, 15 I'd be very surprised if you can hear 20 kHz.

I added tiny self-adhesive radiators (like 5x5 mm) to all the MOSFETs on the cytron boards. Just to be safe. But they don't get warm to the touch, so I guess they were not necessary. The drivers seem to be very efficient.

In hindsight I would have recommended to go with Sabertooth 2x32, though. It took me a long time to find a working way to handle regenerative energy. The Sabertooth comes with a good solution for that straight out of the box. However, some (lots of?) people seem to have success using simple methods I am sceptical of (like using diodes to prevent the regenerative energy to go anywhere). Maybe I shouldn't have complicated stuff like I did.