Newbie from NZ

[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

[rjsutton]

all
just a photo of the top of the panel where the ballscrew would attach, image screw fixed by bearings ( on its side) on the 60mm upstand
the ball housing fixed down where the 8 screws are
I took video but can find compatible file to attach here
thanks Richard

just noticed my other drawing didn't come over
might help visualize

[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

[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]

Andy
THATS why i joined this forum. It's all just numbers to me which i dont understand at all.
Thank you
My wife was interested in the "whipping " issue but told her it was for the machine in the garage. She soon lost interest.
The motor could be an issue as i dont think i can get to 64V in vehicle but well see if someone else can help out
appreciate your time spent on my dilemma

[mekanik]

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


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

[rjsutton]

Thanks for the link
i need a unit with right angle drive ( takes up less horizontal space) so the only ones sort of max out at 470rmp but need an encoder to set limits (i think?????)maybe not i dont know on this part either
could someone please check this out. im still not sure about torque etc . so appreciate feedback-comments
Thanks in advance
Richard
https://www.ebay.com/itm/1pc-High-to...m/264289703688

[Doddy]

Thanks for the link
i need a unit with right angle drive ( takes up less horizontal space) so the only ones sort of max out at 470rmp but need an encoder to set limits (i think?????)maybe not i dont know on this part either
could someone please check this out. im still not sure about torque etc . so appreciate feedback-comments
Thanks in advance
Richard
https://www.ebay.com/itm/1pc-High-to...m/264289703688

Don't overestimate these Chinese motor/gearbox devices. I've used a couple in the past for raising a poly tunnel vent panel (28ft panel of polythene wrapped around a lower 1" steel tube... rotate the tube and the tension on the polythene sheet either raises or allows to lower the tube, opening or closing the panel). They are adequate provided that they're suitably rated but for my application I normally go for 0.5-2 rpm models to get the necessary torque. I have had to replace them, but the environment (heat, humidity) is pretty severe. Part of my selection criteria is the worm gear to allow it to hold position without power. I don't know the actual power output from these but a similar 470rpm 12V Chinese motor/gearbox here (https://www.ebay.com/itm/DC-12V-24V-....c100008.m2219) claims 5kg.cm which translates to around 0.5nm.

Andy's recommendation of a 4nm rated motor is appropriate for a stepper motor - where you need to guarantee the step, or micro step in time to maintain a (potentially) rapid acceleration under load. In your case you're not quite so constrained and I think you can tolerate a lower torque to allow the motor to accelerate more gradually and less predictably. Even so, the order-of-magnitude difference is a little steep. Personally I'd trade the RPM for more torque (1rpm = 10mm with the 1610 screw, 900mm = 90 rotations, so the 260rpm motor would double the torque and give you a 900mm traverse in 20 seconds).

Limiting your choice to motors with integral encoders will reduce your choice of motor drastically. It's easy to add an encoder onto the shaft of any gearbox output (or better - if you get a twin-shaft one). The resolution of the encoder need not be so great - that one you link to is coupled to the motor shaft, not the gearbox shaft, so you're going to be counting small fractions of rotation of the output shaft - no need for this precision, provided that you have a positional sensor (e.g. micro switch) on the closed-position to avoid gradual drift in positional accuracy.

The motor controller is likely to be a dedicated device - a micro controller (maybe the Arduino range) with a H-bridge driver, and hook up the encoder accordingly. That's the easy part.

[rjsutton]

Doddy
i think you may mean don't "underestimate" Chinese motor-gearbox as you seem quiet happy with there performance. !
thanks for your input and your Logic seems sound
Loose a bit of rmp for Torque.
I came here to find out what parameters i need to make the Ballscrew work and i think im nearly there

I had a look on Arduino website and im more confused than ever..H-bridge driver ! STK500 Protocol ! ICSP Header.! loT Bundle......
i will have to join their forum to get answers on how i get the motor to stop at one end and reverse and stop and go forward and stop and reverse.......... I love your comment "That's the easy part " mmmmmmm.
I thought by buying a motor with a built in-on encoder then i would just pick up a controller with a few buttons to press when the limits were where i wanted. Not be be it seems ,
I was going to use 2 micro switches to limit travel but i still cant work out how they must be wired to stop travel and reverse the next time the controller button is pushed. My Bob the builder brain doesnt work very well in these situations
Thanks again
Richard