Dynomotion

Group: DynoMotion Message: 57 From: kepello Date: 10/2/2009
Subject: Need help selecting components
Need help determining stepper/servo motors and DynoMotion products.

Machine is large (5'x10') CNC Gantry Router with two heads. Rack/Pinion on all 4 axis, with gearing on all axis. Currently outfitted with stepper system, step/direction, but is very slow and underpowered. Easily drops steps and looses position.

Want to have closed loop system. Can I do that with DynoMotion product using Steppers? I will need to upgrade steppers, so should I consider a servo system instead, since I want closed loop?

Would like to keep cost for controller boards and 4 motors to under $1500. Reasonable?

Thanks!
Group: DynoMotion Message: 58 From: Mark Stewart Date: 10/3/2009
Subject: Re: Need help selecting components
there is not really enough information provided to recomend a motor size. we need to know running torques and gear ratios of  rack and pinion to give you a proper force and speed rating.
You say your steppers are undersized and drop steps. What size motors are they? for example NEMA 23 and  1 stack 2 stack etc? Do they have a part number or current/torque rating? If we know what motor almost works we can use that as a starting point to recommend something bigger.
 
Also you can use stepper and or servo motors and close the loop with proper encoder feedback. There are differences in how each work but for practical purposes you can go either way. Servo is better as the controller can control the current to the motor and provide better position loop control but if sized properly you will be ok either way.
 
You can maybe buy motors with encoders off of ebay to get under $1500 but with new industrial motors and encoders on the retail market you will probably be tight on budget at $1500.00 you say 4 axis. It there a dual Z or something like rotary table? Also maybe consider Brushed DC motor with encoder.
 
 

 

Group: DynoMotion Message: 59 From: kepello Date: 10/3/2009
Subject: Re: Need help selecting components
Unfortunately I purchased the machine used and do not have specs. I can remove covers and measure gears and racks, and will get back with that information.

I have a dual head (Z and W), thus the 4 axis. No rotary table.

Current stepper motors are NEMA 34 sized, RapidSyn 34D9314A steppers on head axis (2.2VDC, 7.0 AMP, Class B, D.C. 7/95), Applied Motion Products 4034-338 (2.4VDC, 7.0 AMP, 450 OzIn, Class B, 200 Steps) on X and Y. X axis uses a jack shaft to drive both gear/racks rather than dual steppers.

The steppers on the heads (RapidSys don't list OzIn but they look beefier to me).

Never worked with Servos, several smaller hobby type machines with steppers. Can you compare the effective torque based on OzIn ratings? How does the torque/speed cureves compare.

Sorry for all the questions. Just want to get it correct!

--- In DynoMotion@yahoogroups.com, Mark Stewart <fullottoman@...> wrote:
>
> there is not really enough information provided to recomend a motor size. we need to know running torques and gear ratios of  rack and pinion to give you a proper force and speed rating.
> You say your steppers are undersized and drop steps. What size motors are they? for example NEMA 23 and  1 stack 2 stack etc? Do they have a part number or current/torque rating? If we know what motor almost works we can use that as a starting point to recommend something bigger.
>
> Also you can use stepper and or servo motors and close the loop with proper encoder feedback. There are differences in how each work but for practical purposes you can go either way. Servo is better as the controller can control the current to the motor and provide better position loop control but if sized properly you will be ok either way.
>
> You can maybe buy motors with encoders off of ebay to get under $1500 but with new industrial motors and encoders on the retail market you will probably be tight on budget at $1500.00 you say 4 axis. It there a dual Z or something like rotary table? Also maybe consider Brushed DC motor with encoder.
>
>
>
>  
>
>
>
> ________________________________
> From: kepello <carl.lance@...>
> To: DynoMotion@yahoogroups.com
> Sent: Fri, October 2, 2009 7:58:09 PM
> Subject: [DynoMotion] Need help selecting components
>
>  
> Need help determining stepper/servo motors and DynoMotion products.
>
> Machine is large (5'x10') CNC Gantry Router with two heads. Rack/Pinion on all 4 axis, with gearing on all axis. Currently outfitted with stepper system, step/direction, but is very slow and underpowered. Easily drops steps and looses position.
>
> Want to have closed loop system. Can I do that with DynoMotion product using Steppers? I will need to upgrade steppers, so should I consider a servo system instead, since I want closed loop?
>
> Would like to keep cost for controller boards and 4 motors to under $1500. Reasonable?
>
> Thanks!
>
Group: DynoMotion Message: 60 From: Mark Stewart Date: 10/3/2009
Subject: Re: Need help selecting components
I am familiar with the Applied motion motors. I know the RapidSyn is a Superior Elec/Danaher motor and I have used their Servo SloSyn but never the stepper RapidSyn.
 
It is hard to tell w/o looking at machine but 450 oz/in should be more than adequate. I am not sure why you are missing steps unless there is some mechanical binding (dry bearings or unmaintained racks etc.)  I don't do very much with rack and pinion. We usually use screw or belted actuators so I may be off on torque. I have a gantry table with 5 foot x, 4 foot y, that has Parker NEMA 34 3 stack motors I do not remember the torque off the top of my head. It is a screw system and never stalls .
 
What drives do you run them with? Are you sure you have enough Bus power to push motors at rated speeds. I solved a stepper problem last week with an IMS 34 motor with integrated controller/drive. They could move slow however at 50% rated speed it started missing steps with no load. Replaced low wattage power supply with some real power and they are running 100% w/o missing steps. Their application only called for about 45% of rated torque /speed and they thought it would be ok. Their linear supply couldnt keep up.
 
As far as steppers vs servos they are completely different and is best to look up models ratings on manufacturers site. One of the main things as far as torque goes a stepper develops 100% torque at 0 speed and will loose torque as you go faster, a servo ramps up torque as it needs it. Steppers can develop torque faster and at a slower RPM. As the speed increases the servo will outperform the stepper until saturation at max RPM.
Mark
 

Group: DynoMotion Message: 61 From: kepello Date: 10/4/2009
Subject: Re: Need help selecting components
Collected some further information:

Machine requires 1056.25 steps per inch with stepper driver set at full-step mode, steppers requiring 200 steps per rotation.

If my math is correct, that means to travel at

200 ipm requires 1056 RPM
400 ipm requires 2125 RPM
800 ipm requires 4250 RPM
1000 ipm requires 5281 RPM
1200 ipm requires 6337 RMP

I would love to see 1200ipm rapids, but think I could live with 800-1000. Right now my top speed is rapid at 400ipm, cut at 200imp without serious step loss. I suspect but have not confirmed that I am even seeing some minor loss at this rate.

I also found this note from marris at geckodrive.com (http://geckodrive.com/faq.aspx?n=783775)

A.) Round steppers use rare earth magnets, and lose their magnetization over time. Because most of these were made in the 1980's and before, they have already lost a substantial amount of magnetization. Square steppers use permanent magnets however, and provide much higher torque than their round brethren.

I do have round steppers that were likely produced in the 80's given the manufacture date of the machine and my suspicion that they are original....

--- So, am I exceeding the torque / speed curve with old, worn out steppers?