AC Gearmotor sizing

Greetings everyone! I've been scouring the internet for the last few weeks learning everything I can pick up about motion simulators, and motion platforms, and I'm finally at the point where I think I know exactly how much I don't know.

I'm looking to build a 3 DoF Stewart style platform using 3 phase AC motors and VFD's in this style;

although not nearly that robust. The platform would only need to hold the weight of a single person, say up to 100kg, plus the rig itself at 50kg.

I'm having issues figuring out exactly how large the motor and gearbox have to be to support and move the weight of the platform. I did radial shaft load calculations that said a single 3/4 hp motor connected to a 50:1 ratio planetary gearbox could support 220kg of radial load. This seems wrong to me, or possibly I'm not taking into account the acceleration forces involved in moving the platform with a person and rig on top, but it seems like that would support a small car on top of the platform with 3 motors.

I've tried searching these and other forums for answers, but I can't find anything definitive. I don't want to undersize the motors and end up replacing the gearboxes in 3-6 months.

Thanks for your time and consideration everyone, I have a ton more questions, but I'm going to keep it 'simple' to start with

Hi @DMUSER ... try this .
http://www.designworldonline.com/10-points-to-consider-to-get-the-gearbox-you-need/

Hi speedy, thanks for your response. The article made some really good points about general selection and requirements of gearboxes, but it didn't really answer my question. I'm looking for information that is more specifically geared to maximum shaft loads on AC gearmotors.

It's quite likely that the answers I'm looking for aren't easy, but I'm hoping that someone here might have some information they are willing to share that could save me hours of legwork calling manufacturers and speaking to engineers to get my DIY project planning off the ground, and maybe even shave some cost off the project.

How to calculate gearbox ratio and torque?

Hello DMUSER,
I spent 2 years researching before I settled on my motors/gearheads - and this was looking at the CKAS and several other platform manufacturers.

@speedy - where were you at with your link two years ago - good stuff - Thanks

In any event - I'm using 1hp motors (CKAS uses 3/4hp) - I'm using worm gearheads, very heavy duty - at 60:1 or 30 rpm, which I can speed up with my VFD's....
In calculating my u-joint/etc. top platform 3'x5', the RS1, monitor, monitor stand, my body weight, total is 435 lbs - my gearhead is heavy duty and will output 117 ft.lbs torque, EACH - so in some cases,
it's overkill by many of the set standards - I have about 1,000 US in the three motors/3 gearheads - whereas, IF I had gone the SewEurodrive method, I would have spent a minimum of 2700 US...
AND my motors and gearheads are new......IF I had paid list price, the cost of what I have, would have been an easy 2800 US....

I would have loved to have had a calculator to figure all of this - but all the hours and all the local professionals, and all the searching for many months made me more knowledgeable of what I was getting and
getting into.

I do know for sure that I'll have more than "enough power and torque" to handle my build.

Let us know how you're progressing. There are "heavy-weight" members here that have forgotten more than I know at this point and they are great folks willing to help any way they can.

Have a blessed one,
Tom

Thanks for the replies everyone. Any information is helpful in making my mind up.

Tom, do you know the approximate diameter of the output shafts on your gearheads? Do you know if I'm supposing correctly that axial torque limit = max physical weight the gearboxes and shafts can bear?

I know that some builds use supports under the platform itself in the form of a u-joint or other to bear the weight, but I'm trying to figure out what the commercial units use to support the entire platform without that. I'm home next week, so it's looking like it's time to call some gearbox manufacturers.

Thanks again Tom and speedy.

DMUSER,
I "know" what you're going through........but "me" didn't have a calculator - so I talked with friends with engineering degrees, talked with a church friend who owns a motor repair firm, and searched all I could with the professional manufacturers', obtaining what I could. So, in summary, I bought what these folks said was "overkill", but I wanted to be safe as well as able to increase output with vfd's.

My output gearshaft is 1 1/8" in diameter and the gearhead weighs 85 lbs - they are absolutely built like a tank - Boston Gearheads....

In US, there's a large distributor, Automation Direct - http://www.automationdirect.com/adc/Home/Home - that has everything - VFD's / motors / gearheads / just everything and the prices are very good - free shipping in US on orders over 200.00 US......they offer a real nice gearhead in many ratios and shaft configurations, as well as dual shaft. I use their MicroMax Inverter Duty Motors - 3 phase, 1hp, 1800 rpm -
but I got ALL my motors and gearheads, new, for around a 1000.00 US.

I am using a heavy duty "truck" u-joint - my plates are 3/16" and 1/4" plate steel - my frame is out of heavy wall 1.5 x 1.5" steel tubing. MOST professional / commercial companies are using the same...
so I know I'm more than safe. Cannot answer your technical ???? on axial torque etc.....I'm not that progressed in engineering.

Stay in touch - and what I have found - don't stress out too much - it DOES come together..

Have a blessed one.
Tom

Thanks @cthiggin ... Mmmm two year ago "May be I joined the revolution" ...

@DMUSER ... Axial torque can't directly compared with the weight ... you must first provide the mechanical arm length that will actually left that load "half the travailing distance for a crank arm " ... the shorter it is the greater power you get from the axial output torque and the smaller travailing distance becomes ...
To find the output force of the crank arm you divide the Axial output torque in [Newton/meter] / [crank arm length in meter]
Read more here ... Calculating Torque of a Crank Mechanism

There are more information out there to read if you just Google using photos with the right question ...
-How to calculate the output force of a lever ?
-How a spring works ?
-How a pulley works ?

this site have tones of good stuff ...
http://www.designworldonline.com/