Which one? Teknic Servo or AC with VFD

[jmacfarland]

Looking to build my first simulator, a 3DOF balanced platform like @futuresims. Trying to determine what motors to use. Don't need to lift much, 500 lbs max but would like to move that load quickly. Lately the Teknic motors have come up a lot for their ease of use. Looking at this one:
https://www.teknic.com/model-info/CPM-MCVC-3441S-RLN/
First, at only 13NM, I'm concerned that I'll have to get a worm reducer, and second, that adding the gearbox will make moving the platform quickly (>300mm or 12"/sec) difficult. These motors don't get as much torque unless you keep the speed low already. Further reducing that speed (more torque) would keep me pretty slow, right?
So I guess I like the fact that the Teknics don't require VFDs and a ton of sensors to run, but am I better off just going with big AC motors, say 1.5 to 2 HP and some 56C gearboxes? Those boxes are a lot easier to find and cheaper than the NEMA34 boxes for the teknic...

Jeff

[tronicgr]

I used exactly that Clearpath servomotor for my ffb steering wheel that I made a few months ago (check my YouTube videos...). Its strong. Once I burned my palm trying to stop the wheel that started spin out of control ( > 600rpm) as I use it in pure torque mode.

But be aware that the power supply cannot sustain more than 30% or power for long, it uses big capacitors to store the energy that the motor uses or to absorb regenerative voltages. If you use it with worm gearbox that can hold the load between motion cues to allow the capacitors to recharge, you will be fine.

Someone in Germany is building a 6DOF with the same motors but PV model for use with pulse burst mode. I think I have video of it in the AMC1280USB support forum... cant place links with my tablet.

Thanks
Thanos

[jmacfarland]

Thanks Thanos and sorry I didn't reply sooner--didn't have my account settings to notify me on replies. I saw that video and also watched the one you made on Pulse Burst Mode, both very helpful. Not sure if I understand the torque mode. Wouldn't that require additional position sensing? I noticed in your wheel video that maybe you're using an optical encoder or something to read the RPMs? Basically, I want to choose whatever will be easier to control in the long run, even if it costs a little bit more. The PV is obviously more expensive, but if I'm not mistaken can control speed, position, force all from the pulse?

I was looking at the motors again and I noticed that the 3441S has a max RPM of around 800 but really only gets full 13NM torque at around 200RPM. The 3441P has only 6.2 NM but keeps that torque all the way to around 1400 RPM with a max of 1800. I'm not good at this, but it seems like the 3441P geared at 40:1 (maybe 75% efficient) would get up to 35RPM and higher output torque (up to 185NM) than the 3441S? Again, I might not be doing the math right. Any advice is greatly appreciated. In your experience what's the best RPM for a flight & racing sim?

Thanks for your help and for all you and others do for this community.

[jmacfarland]

My gearboxes are on their way and I will hopefully be building soon if i can find the time. Question about Pulse Burst mode: The Teknic motors with pulse burst positioning run in only two speeds. Will the positioning be slow and smooth when I move the joystick slowly or will it be a series of short small bursts per each update? I ask because in my mind it seems more "fluid" to purchase the cheaper Teknics with follow velocity command and close the loop with potentiometers on the shaft and use velocity mode on your board? I need to have a wide range of speeds, and am concerned from what I know about PB mode that it will always be super-fast or super-slow? Maybe I'm just thinking of this the wrong way.I watched your video on PB mode and still not quite sure...

[tronicgr]

Have a look at my last two videos on my YouTube channel. The ones with just "follow velocity command" are better to use and will provide fluid accelerations and smooth motion as well not just two speeds of the pulse burst mode.

So yes, the cheaper model with no pulse burst would be perfect.

Thanks
Thanos

[jmacfarland]

Thanks for the quick reply!
Last question and then I promise not to bother until I get your board (after I get the motors). My gearboxes are 25:1. Your latest videos I assume are of the 3441S with max speed of 800 rpm and 13NM torque. Wondering if I'm better off with those or the 3441P with max speed of 1800 rpm and 6.5 NM of torque. The 3441P appears to have a more constant torque curve with lower torque but constant up to pretty high RPM...

I obviously want the highest torque possible but concerned I won't get that high torque very often unless I'm maxing out the motors all the time. Thanks again.

[tronicgr]

The 1800 Rpm motors will give you 72rpm after your 25:1 gearboxes, that is a little too fast.

Normally I recommend using 10-15rpm after the gearbox for 6DOF platforms.

Using the clearpath motors with the 800rpm and higher torque you will get that 15rpm with high torque as well (32 rpm max).


Thanks
Thanos

[jmacfarland]

As always Thanos, Thank you.

[autoliv]

So After all what did you choose ?

I also seem to go with ... CPM-MCPV-3441S-RLN .. but not sure what you guys mean to choose one without pulse burst mode and what extra potentiometers you need on the shaft. I thought the ideea to go with teknic servos is that you will save from the costs of implementing aditional driver and encoders for this motors.

What would be the function of the potentiometer ? Will this stay on the shaft of the gearmotor or on the shaft of the motor ?

Thanks. Please give more infos and credits if you already build this .. as I'm just about to start this project.