Showroom **RIP** - 6DOF project using 12v DC Motors, Sabertooth 2x60's (was MM's) and Arduinos + OSW

Ahhh yes well you may have a valid point there @tronicgr . Still not sure about the caps but I think diodes may be a good shout didn't think about that to be honest. Thanks a good constructive comment I like it I will look for some diodes now infact

Also having issues with the weight distribution way too much on the front 2 motors they are overheating and the middle and back ones a barely warm.

Need to move everything back on the platform get it more even .

@tronicgr Can I just put some diodes on the motor cables stop the power back tracking to the MM's ?? Not sure if I'm right or not 600w 37amp spike diodes I have seen on fleabay will they work ?

I don't need the caps for the psu's as they do not trip out or are you meaning something totally different ?

No you will need to wire the diodes back to the power supply, and if you don't use capacitors to store the extra power it will end up back to the MM's. The PSU has spike protection, the MM's not.

OH MY GOD! That thing looks epic. Do you ever sleep???

I may be coming over to the UK next year and I MUST CHECK THIS OUT IN PERSON

Ah, the joys of development . Figured you were having some issues when a video of you riding your rig did not pop out the next day. Have you stuck a cro on the output to see if you can catch any spikes? Although motor magnets slipping inside the housing does not sound promising for the life of your MMs.

Just for your information, below is something that I have posted before in regard to the chips used in the MMs. Just something to be aware of - Manufacture recommends 500uf per 10A load . MMs comes with 470uf fitted for each chip and there is spare space on the board for another. Read the note below:

So 500uf per 10A... There will be peaks of 100A... At least

Why I use a DC battery as recommended by manufactures to capture the back current generated by the h bridge. I have heard on lithims being used but don't like the idea, I know how to store a gel DC battery and safely work with it.

Thanks everyone for the advice, i have been in London for the weekend.

I will get some caps and put them on the mm's . I will have to measure the current coming back from the motors see what it is.

If that fails i will use tronics way.

I've ordered some 1000uf caps to go on the MM's so will have to see how they go.

So the build is on hold till I get the parts delivered

@SilentChill you are using the MMs as a dual half bridge so really I cannot imagine you are going to overstress the MMs in any way

No neither do I @Pit but the back current from the motors could be why so many MM's have died.

my MMs did not die while "working", one died due to bad soldering, one died due to a short circuit. I have driven 1000 hours now on the MMs - no (more) fuses and no caps.

I agree with you @Pit because I ran my 3dof with no issues at all for nearly 9 months .

Perhaps I will sort the weight distribution out while wait for parts.

I would also be looking at your motors/gearboxes, just in case there may be some other issues in play there under load? Worm screw gearboxes are known to bind once they reach their max load ratings and good lubrication is quite critical because of the way they work. Also you are using second hand ones . Maybe a service on the gearboxes? Your current readings should although hopefully show this up.

Maybe, but don't forget, like me he is using four driver chips per motor.

I'm sure there are no issues with the gearboxes they are all very very smooth. Its a totally sealed unit with lifetime lubricant in them.

Most of the motors were seized I had to open them up clean and reset and glue the magnets.

I have moved everything on the platform back 250mm it has spread the weight nicely and now no motors are overheating however the motors with only 1 MM are not strong enough they keep cutting out.

I've taken all the MM's off now and tested individually, my results are shocking. Out of 12 MM's I got 6 are just not working at all, 4 have issues with either side of the motor outputs. I think I got a very bad batch from China. The ones I took from my old rig are still working perfectly, just a nightmare.

The chips are furked on the MM's simple as that, I have now some half and 3 quarter brdiges to use so will have to see how I get on till the replacements arrive.

Onwards and upwards, the back current from the dives is negligable not enough to damage anything.

All the problems I have had are down to bad MM's.

Nightmare these MMs are a pain for not working right out of the pack I guess they are made so cheap, I had 5 and only 1 worked correctly.

Fingers crossed for your replacements to be from the good batch

Sorry to hear of problems with the MM's @SilentChill. Btw, what is the ratio of your worm gears? I was just thinking that if you are using 50:1 or higher ratios, your motors should not be easily back driven if at all. If this is the case I don't think you should have problems with regenerative currents.