Delta rep rap kit

I am new to the reprap community and wanted to guage the viability and interest in a deltrap kit. This kit will have the following paradigms

- based on metal gear digital hobby servos (which will require extensive longevity testing)
- stepper motor upgradeable the hobby servos is for entry level as this reduces the cost
- require limited hardware, and electronics. the main reason for the delta would be cost.
- brains would be arduino mega or equivalent with no need for extra drivers all jacobian to GCODE translations will be done on chip
- bowden extruder - dont know what the driving motor will be yet
- usable build area is 5inchx5inchx5inch however in reality this is larger but no longer linear.... if you have a flater peice you can build 8x8x2...
- desired speed is 200+mm/s with theoretical numerical accuracy of about <.015 inches worst case. this accuracy is geometrically non-linear.
- machine size is about 8inchx8inchx12inch and aims to be easily setup and torn down
- offered one time on kickstarter or indiegogo and after the campaign the complete build will be open sourced regardless of success
- final design will be in metric, but some of our design parameters are in imperial at the moment

Any opinions and suggestions are welcomed. We dont have a good name yet and aim to have a first working proto by March.

A servo-based delta bot would be nice, but is it accurate enough?

---

Frédéric

From preliminary calculations and simulations the very worst case positioning error is .015 inches which is the just smaller than an average nozzle size for ABS. This would allow for single pass thin wall structures. With gearing a stepped motor upgrade can be better but the complexity and cost increases quite a bit.

Very interesting, would you have the necessary torque to move the extruder and its support with hobby servos? With which speed will it move? i've already thought about something similar but had to abandon the project because it would have been very slow. You said the speed you expected it's of 200mm/s... What would you use? Stepper or hobby servos? Can you please tell wich specs you expect?
thx
Max

I think this would be popular if you achieve what you state, but it will be very difficult to get a delta to this sort of accuracy.

Delta robots are notorious for tool head shake due to the long arms in the mechanism, so your actual machine accuracy (not resolution) is likely to be very low. Just go to youtube and type delta robot, then watch the tool heads of the robots. They wobble and shake which is a big restriction for this type of robot and the main reason why they are not more widespread.

There is an additional problem in that if the machine is not set up exactly, for example the arms are not exactly 120 degrees or the rods are not identical in length you get bowed or twisted parts. This would make it very hard to lay down the first layer of a printed part, where Z height is critical. This can be a project killer.

The work envelope you quoted is quite small so this helps with accuracy, but you will find in order to accomodate even that area your arms will still need to be quite long and the joint articulation large. This in turn makes the machine much bigger than expected (and of course less rigid and more costly).

Good luck with your project and even if you don't achieve all your goals, another delta robot in the reprap community is always welcome.