Just another 3DOF build

Hi, watching other builds inspired me to build one myself. There is a lot of information in this community that just reading old posts help me get where I'm at. But one thing that I did not expect until I build and felt it my self is the slack the gear motors have, or maybe the ones I got. Attaching few pics of my build, if there is anything you see it can be done better, let me know.

Few years ago I build table side CNC with step motors and was used to not seeing any slack. Maybe that is expected with those jazzy motors but it questions me if I pick the right motors, adding springs or damper will put stress on motor and possibly jerky motion, so I have few questions for people that have more experience in this. I'm OK, with refabricating and modding the frame, just the slack on those motors eats on me. I'm using 12v battery testing it now but I don't think with 24v would be any different other then withstanding the load better.

For anyone that can help, my questions are:
Is there a way to somehow reduce the slack? Maybe I mounted the connection rods in wrong angle? Any suggestions appreciated.

If I just strip the gear box from jazzy motor and use lead screw with those motors, do you think they will have enough torque and how many turns per inch the lead screw would be recommended (I'm guessing the more turns per inch the better but not sure)

Thanks!

Thanks for quick replay! I totally missed that about the longer the lever used the less efficient the torque and more slack. That makes sense. Ok, this gives me idea and will keep me busy for the weekend, thanks again.

1. the configuration of your 3DOF seems different from most of the projects on this forum, the angle between the motor arm and the rod should be 90 degrees, in your case the rod is parallel to the arm ?
Watch this thread to see the most efficient assembly
https://www.xsimulator.net/community/threads/diy-3-dof-inspired-by-dof-reality-h3-model.18273/
2. You wrote little about the power supply configuration, if you are powering 24V motors from a 12V power source you are significantly reducing their power which is certainly not a good idea.

Max speed (RPM) is proportional to the supply voltage. Torque is proportional to current. So powering a 24V motor from a 12V supply still delivers the same torque but only half the speed and power.

However, stall torque is also proportional to voltage (stall current = voltage / winding resistance). So if your drivers can deliver more than the rated (continous) current of the motor you might also see a decraese in peak torque.

Attyla.pl thanks, I'm new to this and at the time of the build it made sense to me but now I see I was wrong and correct it this weekend. By moving the arms to new location and making them 90 degree to the rod made a whole lot of difference. I can live with it now, the slack is much smaller then before.

AErosmit, good info! Do you have any suggestions is 24v power supply? I'm still in testing phase and had 12v battery on hand to test it with, but I'm sure 24v I can only imagine that 24v would be better all around. Thanks.

Most people here use 12V server supplies and connect two in series to get 24V. How much current can your motor drivers deliver? From the pictures I can only guess that each motor can take probably up to 20A. That would be 20A max. for 3 motors or 24*60=1.4kW. So two server supplies of 750W would be surely enough. But I think that's overkill.

If you use two 12V batteries in series and charge them with SMPSs I think a single 320W supply should do.

Perfect, thanks for the advice, this give me an idea for tonight I have spare EVGA 1300w PC power supply that has 6 PCIE connector ports, I think I'll use that. It's beefy power supply so it should take the load.

Be careful with PC power supplies. Some require a minimum load on the 5V and 3.3V outputs for the 12V to work properly. Check the data sheet.

Hello, Can I ask you the information and spec on the motor you use?
They seem to have wheel stud, are they originally for a kart or dolly?

Hi, those are jazzy motor's. Yes, they have wheel hub on, they are from a wheelchair, I could not figure out how to remove the wheel hub so I left it and used it. There is plenty of them on ebay, I got a pair for about $80. This particular is 29:1 ratio from what I can tell. It works fine but from what I hear the higher the ratio the better but maybe someone else can chime in on this as I'm new to this. There are other jazzy motors that are 50:1 that work smoother but they are more expensive.

I'm running them on computer power supply (EVGA 1300w) using GPU cable runs. I couple two GPU cables for one motor, this keeps 12v but holds higher amps. When I couple the GPU cables to get 24v instead of 12v the power supply used to cut off and had strange issues. Running two GPU cables per one motor and still keeping it 12v worked fine.

Thanks for the reply. I am still learning and searching hardware for my Rig, I will look at those motors.