Newbie from NZ

[AndyUK]

So I've thrown your numbers roughly into our motor calc spreadsheet, which is only a guide, but has a few nice assumptions which lead to a wide safety margin.

Assuming your ballscrew is 900mm long (which obviously results in a travel less than 900mm), a 1610 screw (for speed rather than accuracy) and a moving mass of 90kg (you said 400N load, but the spreadsheet wants a moving mass - so lets take the chair plus ~20kg of frame).

If the screw is fixed-supported (i.e. BF and BK mount) we get a critical speed of 2200 ish rpm before whipping is an issue. That means we have a travel speed limit of 22m/min, well in excess of what we need. Assuming a 15s ish travel, lets say 6m/min which could travel the full distance in 10s but allowing time for acceleration and deceleration. That nicely translates to 600rpm on a directly coupled motor.

All in, you need a torque of 1.34nm (ish) at 600rpm to achieve that. Make it 4nm to allow for dynamic loads and a 3x safety factor.

Now, here comes the issue. Motor selection. I'm not great with low voltage motor selection - so I've used a 12.5nm nema34 stepper at 64ish volts. This easily gets you to the 3x safety margin that the spreadsheet suggests, but isn't exactly straight forward to use in a car. I'll let someone else chip in at this point :)

MotorCalcs-rjsutton.xls

[rjsutton]

Hi Mekanik
just wondering if the comments etc can be transferred to the mechanical general forum instead of the newbie thread? or doesnt it matter ?
thanks Richard

[mekanik]

Hi Richard
Lee will move your post to the appropriate section if need be.

[John McNamara]

Hi RJSutton

The following link will assist you to find a 12V Gearmotor.

Armed with AndyUK's motor computations you will find a number that meet his specifications.

Beware of selecting the motor/gearbox on price alone You want your lift to long lived and reliable..

https://www.google.com/search?q=high...w=1195&bih=731

Regards
John

[rjsutton]

Doddy
Thanks for that
The $ cost of the motors etc is not a problem. But if these won’t work then I will be in another place
Appreciate any help in program and wiring diagrams. Any of your guys knowledge I can glean then that is a 100% more than I started with
Thanks
Richard

B


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[Doddy]

Doddy
Thanks for that
The $ cost of the motors etc is not a problem. But if these won’t work then I will be in another place

For clarity, I’m not convinced that these motors are big enough. I think they will be operating at their max power rating to get close to what you want, but then you’re only looking to run for 20 seconds at a time under load. This is why I say you’re in the land of practical experimentation

[rjsutton]

Doddy and All
Mate the next thing ive found is
https://www.aliexpress.com/item/3290...chweb201603_55

they reckon ( i think ) that @ 220rpm then torque is 24.25 kg.cm is this 2.4NM ?
alot more expensive but will see if i can source a cheaper supplier $NZ -$US not very good exchange ( thanks Trump)

I hope i could put an encoder somewhere ( can it go on the end of the ballscrew?)
Richard

[Doddy]

I’m not going to comment on the motor choice other than to say it looks much closer to the numbers that Andy suggested. I’m guessing the rating is more appropriate for continuous rating than peak (a good thing)

To answer your question: you essentially want to add an encoder to the gearbox output, either directly or on either end of the ball screw.

You will always want a “home” microswitch close to the home position for the mechanism to reset/calibrate the closed position... that allows you to include soft stops on the traverses by predicting position.

[rjsutton]

Thanks
Can You "suggest " an encoder and controller setup that would do what you mention. Im not sure where (or How) a Home microswitch would be wired into the circuit to reset-recalibrate.
If not too much bother could you please give me a diag (or lead me to where i would find one) with the encoder wire and microswitch.
I do think those chinese motors would not work as they just too small. I don't want to WASTE time and money . I will have to shorten the ballscrew slightly to fit the wider gearbox in as well

Andy if your still around do you think the new motor link above will be better choice of power for the ballscrew ?

[rjsutton]

Thanks I would appreciate a diagram when you have the time don’t really understand the relay-diode thing but maybe I see it I can do it
Richard