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]

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

[Doddy]

Doddy
i think you may mean don't "underestimate" Chinese motor-gearbox as you seem quiet happy with there performance. !

No, I meant don't overestimate. These are very small devices, very small motors. They are reasonably rugged (the first that I stripped down was a mostly metal gearbox). I think these are particularly under specced for the numbers that Andy provided - but I'm trying to understand my gut-feel (rather than science) that they might just be worth a look at if the $30 cost is not prohibitive to you. But understand that you'd be in the realm of practical experimentation.

Doddy
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
Richard

If you wanted I could provide the suitable software(or at least the basic framework that could be adapted by yourself) and help advise on the wiring. I'm not promoting Arduino as the only solution here - and at the end of the day these are simply based around COTS microcontrollers, but they do promote an accessible set of capable programmable hardware.

[John McNamara]

Hi RJ sutton

This link points to a 12v DC servo motor search.
Some of these units have an integral gearbox while others don't however if you make sure the shaft and flange mate up many will will work with a separate often right angle gearbox. Servo motors usually have an integrated encoder.

Leadshine offer a good range of servo controllers.and or motors. They are blatantly copied! and it is hard to tell the fakes are so similar. Make sure you are getting the genuine article.

You will need to control this setup with a micro, an Arduino for example.
This approach using servos better quality gearboxes and a dedicated controller will cost more but it should be very long lived and reliable.


Regards
John

https://www.google.com/search?q=12v%...%3Apinterest.*

Worm reducer search

https://www.google.com/search?rlz=1C...4dUDCAY&uact=5

Leadshine servo controllers

http://leadshine.com/Pdf/Catalogs.pdf