Stepper Motor specs for big project.

shortbus

Joined Sep 30, 2009
7,344
Call me crazy but I just opened another can of worms. Space for the motors is very limited, less than 5 in.
but a hydraulic motor can be fairly short like for example- 5.4 cu. in. White, torque 1430 in.
lb. & 1985 intrmit. 4.53 in long. There are inline live swivels available. I don't relish sitting with my chin on my knees with 2000 lb. hot oil flowing around me.
And fairly cheap to as surplus. Or using a hydrostatic drive like in a lawnmower they can be self contained, no hoses to worry about.
 

Thread Starter

AceScottie

Joined Jul 17, 2017
8
Thanks for all the replies.
Due to the motion (3 individually spinning rings) i cant use any hydraulic based system. everything the motor is has to be self contained with only electrical wiring going to it. Getting slip ring mounts for a pressurized system would be difficult and it adds points of failure which is something I,m trying to minimize.

Space for the motors is completely dependent on the the size of the motor. i said the ring would be about 1.5m but that can be expanded and the smallest ring can be as small as 1m so i could have 50cm between them if i need to.

using washing machine motors is a really good idea. and just reduced the cost by a few hundred pound so thanks. plus if im using them i could probably have 6 instead of the original 3.

thanks for all the info guys. if i can get the motors i will post some results and see where they lead me.
 

MaxHeadRoom

Joined Jul 18, 2013
19,703
The Fischer-Paykel motors are outrunners, stator in the centre and the rotor outer, and are intended basically to be direct drive if this is suitable.
Max,
 

shortbus

Joined Sep 30, 2009
7,344
Could you draw a sketch of what you're trying to make? I'm not able to understand how three 'rings' are goint to be able to do what you're thinking of doing. I was thinking it was a steel cage in the form of a ball, but now that you say 'rings' I'm not sure.

A ball type cage it could be done with a cradle with three powered tire in a triangular position. Depending on which wheel was powered it would rotate the cage. But a sketch of what you're making would go a long way to getting better answers on how to do it.
 

RichardO

Joined May 4, 2013
2,271
... at least for a scale model test. ...
This is the best advice I have seen so far.

If you have not made a scale model using a GI Joe as the passenger then you are going too fast. Step back and do the basic research before building big and expensive hardware. Once you have a partially working scale model you can post a picture here for better advice. :)
 

Thread Starter

AceScottie

Joined Jul 17, 2017
8
well i found out this has been done before.
Google "Sega R360" for what this project basically is, although a bit smaller.
to motors used were:
ra12m2-1500r Toshiba motor
rad02-2033s Toshiba drive/amp
i cant find out any info on these motors however.

i have revised it so there are 3 points of motion:
1: on the base plate (Z axis)
2: spinning the sphere on the X axis (outer ring)
3: spinning the sphere on the Y axis (inner ring)

because there is no point (other than the axles) that is fixed i will have to run wires through a slip ring device, this cannot be done with any type of pipes without a potential of leaking or breaking.

the picture i attached should show my working design (its not pretty).
Yellow = inner sphere (inner ring)
Green = outer ring
pink = base plate
 

Attachments

hrs

Joined Jun 13, 2014
179
To simplify things let's suppose that it's just a thin ring and ignoring all of the dynamic effects that multiple ring will have we get an inertia
J = m*r^2/2
where m is the mass of the ring (600 kg) and r the radius (0.75 m).
w is the angular at 30 to 60 rpm = 1.6 to 3.1 radians per second.
t is the time to accelerate to w at 2 to 3 seconds.
a is the average acceleration = dw/dt.
The required torque T is then a*J.

For 30 rpm in 3 seconds I get 177 Nm.
For 60 rpm in 2 seconds I get 530 Nm.

That's a lot of torque. This is assuming your motor can provide constant torque regardless of rpm. I don't know much about electronics but it has been told to me that only variable frequency drive motors can provide constant torque up to a certain speed limit.

It would be best to make the radius as small as possible. Increasing it will increase your problems exponentially. Also try to bring the mass down as much as you can. And maybe relax the acceleration requirements.

I don't think this is going to work on a shoestring budget.
 

Bernard

Joined Aug 7, 2008
5,353
I think the weight is going to come down, maybe a U cross section of rings, 3 to 5 mm thick with sides maybe 3 cm wide.
 

RichardO

Joined May 4, 2013
2,271
It would be best to make the radius as small as possible. Increasing it will increase your problems exponentially. Also try to bring the mass down as much as you can. And maybe relax the acceleration requirements.
Keep in mind that any weight on an inner ring has to be supported by the next farther out ring and so on. This means that for even small changes in innermost ring weight there is a huge change in the weight that the outtermost ring must support and that the motors will have to drive.

Unfortunately, you will be in the inner ring so there is not much you can do about that weight. The most you can do is minimize the weight of the rings and mechanism.
 

hrs

Joined Jun 13, 2014
179
Keep in mind that any weight on an inner ring has to be supported by the next farther out ring and so on. This means that for even small changes in innermost ring weight there is a huge change in the weight that the outtermost ring must support and that the motors will have to drive.
The torque that the motor needs to provide is related to the inertia of the system. If all of the mass was concentrated in the dead center of rotation the required torque would be zero. So it depends on the mass distribution. The stuff in the middle including the human will have less effect on the motor requirements than stuff farther out.
 

Thread Starter

AceScottie

Joined Jul 17, 2017
8
i do plan to balance the middle as best i can, the only thing not balanced will be the person inside.
the will be nothing outside other than some wires, which will also be balanced on both sides.
what i am building it very similar to the gimble ring, however quite a bit smaller.

Thank you for the equations for figuring out torque. however could your wright them down fully using () so i know the orders of operations.
if i was 300kg i got a torque of 134.88 which if i use a decent 10:1 gearbox can be achieved with a 15Nm motor.

However there are still things i dont understand.
I keep seeing motor specs listed as 10Kgcm and whats the difference between torque and stalling torque ?

if i correctly balance the system (without a person inside) i am moving mass around the axle, rather than moving mass outside it.
while googling Kgcm its how much weight i can carry in Kg per cm away from the axle. so 1Kgcm means it can support 1 Kg 1cm off axle but only 100g 10cm off axle. is this correct? and how would this affect my project ?
 

hrs

Joined Jun 13, 2014
179
however could your wright them down fully using () so i know the orders of operations.
J = (m*(r^2))/2 (m in kg, r in meters)
1 rpm = 0.1 radians/second, there's an error in post #29 where I miscalculated the angular velocity by a factor of 2.
a = w/t (w in radians/second, t in seconds)
T = a*J
The result will be in Nm.

I think kg*cm is just an old way of specifying torque.
1 kg*cm = 0.1 Nm.
 

Bernard

Joined Aug 7, 2008
5,353
I believe that a 15 Nm motor with direct drive can start & spin unbalanced inner ring if we are allowed to use both forward & reverse accelerations.
 
Top