fast/accurate linear motion on a budget

[MrPrezident]

I would like to build a juggling machine that can juggle at least 3 balls and mimic the 2d motion of human hands without worrying about the arms.  So I need 2d motion that is very fast (and accurate).  It would be kind of like this machine:
https://www.youtube.com/watch?v=9asDO_1A27U

I was thinking that something like the following linear motor configuration would be great (except I would want two 2d bots instead of one 3d bot):
https://www.youtube.com/watch?v=9asDO_1A27U

The problem with linear motors is that they are REALLY expensive.  I am willing to spend around $2,000, but with quotes that I have gotten on linear motor prices, my budget would be off by an order of magnitude.  I was wondering if there is some other way that I could do this without spending more than $2,000.

I did some calculations, and it looks like I will need something that will be able to move at 3m/s (or actually 8m/s preferable if I want it to throw at different heights).  The max acceleration would need to be 17m/s^2 (or 60m/s^2 preferable).  Does anyone have any ideas?  Linear actuators are generally slow, and the fast ones seems to be expensive.  Maybe there is some servo that I can use with belt or gears to get the speed/acceleration that I want?  The other piece of information is that the balls would be about 100g, so that would be the load.

thanks!
-Nathan

[waltr]

Look into buying from surplus outputs and possibly ebay to get stuff at a fraction of their original cost.
You will need to make some design compromises since exactly what you need will not be available.

[Tommy]

 

Maybe there is some servo that I can use with belt or gears to get the speed/acceleration that I want?

would think this type application could be done using pneumatic slides for a fraction
of the costs of servo.

http://www.ebay.com/itm/Koganei-ORV40X640-Pneumatic-Slit-Rodless-Cylinder-Air-Slide-w-ZE102B-Sensors-ORV-/350837101427?pt=Pneumatic_Hydraulic_Valves_Parts&hash=item51af855373


https://www.google.com/search?q=pneumatic+slide&tbm=isch&tbo=u&source=univ&sa=X&ei=sREIUs-lHrTKyQGQ_ID4Ag&ved=0CEEQsAQ&biw=1366&bih=681#facrc=_&imgdii=_&imgrc=lPZMN8hbFPIFaM%3A%3BXSXuprTBF5kR2M%3Bhttp%253A%252F%252F4tsi.com%252Fwp-content%252Fuploads%252F2012%252F02%252Fbimba-pneumatic-ultran-rodless-slide.jpg%3Bhttp%253A%252F%252Fwww.4tsi.com%252Fmanufacturers%252Fbimba-manufacturing%252F%3B350%3B250

Tommy

[MrPrezident]

Hmm... I've never heard of pneumatic slides, but it looks like they don't have accurate/consistent velocities, which I think would be a big problem for a juggling machine.  The most important thing for an accurate throw would be to have the correct velocity when throwing the ball.

[jwatte]

A brushed DC motor with a good shaft encoder (for velocity) and PWM controller, driving a timing belt, and the pulley traveling along a set of rails with linear bearings, will probably give you the consistency/precision/power you need.

[MrPrezident]

Why a brushed motor instead of brushless?  Is it because they are cheaper?  I'll take a look at shaft encoders.  I understand the concept, but am not familiar with how to use them.  Would that give me the ability to accurately control position, velocity, and acceleration?

[jwatte]

Brushed motors are cheaper, and easier to control, than brushless. You can typically find a brushed motor with gearbox and encoder all built in. Pololu has some nice ones: http://www.pololu.com/catalog/product/1442
Put a small pinion on the motor shaft, and a timing belt, and drive it with a PWM controller and read the sensor. There are controllers that can do both of those functions for you; Pololu JRK; Roboclaw; and a bunch of others.
The one additional thing you need is an end stop, so you know where "zero" is.

[Pogertt]

Here is how this was acomplished:

http://dce.fel.cvut.cz/juggler/

[EddieAutomated]

Try our discounted linear actuators section. You might find what you are looking for there. You'll certainly be able to find something with the precision and speed needed for a project like that.

Cheers,

Matt Edwards
ActuatorZone.com