Seeking genius programmer for lego repstrap

So after quite a bit of time collecting pieces and testing different drives, I've got my lego repstrap well on the way. I'm still working out the kinks in the extruder design, but that's proceeding apace. I hope to create a repstrap that is as completely lego as possible (obviously, the extruder nozzle and heater will not be genuine lego bits). Now I just need a person who is good at programming. My expertise extends to looping RT 90 FD 100 4 times in logo to make a square. There is a lego computer interface that allows sensor readings and motor control through a serial port. I need someone who can modify the existing reprap software, or make new software, that can handle controlling DC motors through the serial port instead of commanding stepper motors via firmware.

For what it's worth, I'm aware that there are signifigant engineering difficulties here. A lego 3D mill for floral foam exists, with very good accuracy, so I know decent accuracy won't be impossible. But really the only signifigant contribution this would constitute is proof that DC motors are a viable option instead of stepper motors. If there's interest, I'll post some pictures, but I doubt there will be enough interest to warrant build instructions. But if you or someone you know would be willing to help me out software-wise, please, please drop me a line.

[www.youtube.com], for those curious about progress.

hi i've had a similar idea, but i'd use lego nxt motors, as they have a build in rotation counter so i think they could be more accurate then stepper motors. there's a website that sells parts to connect nxt motors to an arduino but because i have the same programming skills as you do i haven't got any idea how i'd make a driver. also i would just use the motors, lego gears don't fit into each other quite as tight.

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edward
but i'd use lego nxt motors, as they have a build in rotation counter so i think they could be more accurate then stepper motors

A rotational counter is accurate to one rotation.
A stepper motor is accurate to one micro step (assuming you don't lose any steps which it won't if properly set).

With standard 200 step 1.8 degree steppers with a 1/16 stepper driver this means it is accurate to 1/3200 of a rotation!
Or 3,200 times more accurate then the lego nxt motors.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

AFAIK the NXT-motor has a resolution of 1 deg and an absolute accuracy of around 2-3 deg.

But anyway, microstepping drivers have a much higher resolution and accuracy - some of my steppers have a resolution of 0.036 deg and a (systematic caused) accuracy of 0.1 deg ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

A lego motor shield is described here [blog.tkjelectronics.dk]

The lego NXT motor has a quadrature encoder (optical wheel type) on the motor shaft, and a reversible DC motor with 1:48 gearbox. It has no intelligence, just some conditioning of the encoder outputs I can see. Costs $20.

So you would need to add quad decoder and motor speed control to get a positioning system. To control 4 motors probably pushing the limits of an Arduino, depends on how fast you want to go Would be easy enough for an ARM Cortex I think.

A Lego NXT motor vs stepper motor is probably not cost effective. Of course, you can source DC motor with gearbox and an encoder more cheaply, requires some effort to build it into a neat package. Backlash compensation provides additional fun.

There is no doubt that servos can be used as an accurate positioning system, it would be interesting to see what cost reduction could be achieved.