Step 8: Conclusions, Notes, Room for Improvement

Picture of Conclusions, Notes, Room for Improvement
That's about it. For TeleToyland, we used some PHP scripts to command the servos via an Internet to serial connection to the SSC-32 board, which the servos plugged right in to. If there is enough interest, we may do a separate Instructable on that setup.

Both axes have issues with not quite centering due to the potentiometers - causing the the digital servos to whine a lot at rest. For occasional use, it's probably fine. For TeleToyland, we used a separate servo powered switch to just turn them off when not in use. We may get a digital servo programmer to see if narrowing the dead band will help. Higher quality potentiometers may help, but we may also be reaching a practical resolution limit in this approach.

(June 2009) For the linear slides, we used drawer glides. These are working fine so far, but they do stick out when the XY table is in the home position. So, we are thinking about using 16mm Linear glides from www.vxb.com - that seems like the lowest cost ones around.

(June 2009) Note that for the Y axis (the one on top), the servo motor is working fine, but for the X axis, we have had some issues. So the current system is using a
Pololu 3A Motor Controller with Feedback and a 12VDC 250RPM DC Gearhead Motor. The board from Pololu works just like a servo control board, and we already have the external potentiometer. The motor is much more robust, and has been working well. One minor issue is that the PID algorithm sometimes overshoots a bit, but it's not too much, and the board allows you to set the PID constants - just need time for fiddling. :-) You can also use a servo board and adapt it for the same use - we'll look into that sometime too.

Other Uses
This is an interesting approach, and might make an excellent arm configuration for a mobile robot. The Leaf Project members are interested in arms, and this could be used for part of it. You could even add a counterweight on the belt opposite the end effector so that the arm would balance automatically - as the hand moves out, the counter-weight would move back. Adding a second linear system behind it would allow the weight of the object picked up to be balanced too.

The following sites provided some of the inspiration for this project:
Easy to Build Desk Top 3 Axis CNC Milling Machine Tom McWire
Improving Servo Positioning Accuracy David P. Anderson
ServoCity Servo Power Gearboxes

We didn't use this, but it looks interesting - a timing belt pulley for MXL belts (0.08" pitch) for Hitec servos

We found this after building ours - uses gears in a similar way, and the drawer glides are similar:
Autonomous Foosball Table.

You can drive this project live at TeleToyland
i run the bs2 stamp chip i got over 60 servos around  i been trying to find a way to run servo's instade of stepper motor   im working on a nothere project cnc tipe  but i don't won't to run a 300 board i like to find a nothere way to run it or convert the servo wire's to run with a home made board
akirawind5 years ago

Hi,carls, i have a few Questions here:

Does the Y-axis Drawer Glide system which you did here slide from the bottom to the top of the whole mechnism? I dont understand how did you make the drawer glide slide in the position 'bottom-top'?what does it mean by 'bottom-up'?

As my project is about a pick and place mobile robot,so i would like to make the Y-axis slider to slide from the bottom up to where the top end. Could you teach me? 

flemron5 years ago
very cool! i would love to see how you did your web interface with the SSC-32 board.
This is a very elegant design. I was wanting to build a xy table that was servo controlled with all the expensive hardware, this is pretty much it. Do you think it would be capable of somewhat precise control like within the 1/100th of an inch? What tools is it able to handle, something like a plotter or cutter?