PICAXE with Multiwii?

[h_e_c]

Hi everyone,

I'm quite new in al this bussiness about multicopters. I'm doing a project and I want to use Multiwii, because I find that the relation between its cost and the impressions of people is very good. So I looked into this page and others, but I did not find which microcontrollers do support the Multiwii software. So I'm totally ignorant about this point.

I know that Arduino is usually the people's choice, but I would prefer to do the project in PICAXE, because my teacher will be glad if I do that and my school will supply me with the chips, so the cost will be 0 for that. Has anyone ever tried that? Is it possible to make a bootloader for it and then use the Multiwii program? Will PICAXE support the GUI, or does only Arduino? If not, it is not possible to change directly the PID values into the software, and then try until I get an acceptable combination? And, if PICAXE does not support at all the Multiwii program, it is possible (with a medium knowledge in C++) to make one for PICAXE, or do I have to be an informatic engineer? And, if that cannot be done, what other microcontrollers, apart from the Arduino, work with Multiwii?

Thanks in advantadge, and sorry for my bad English (and for my newbie questions).

[Pyrofer]

C and its variations are meant to be portable.
If you have knowledge of the C compiler you will use on the PIC you should be able to port the code, but it will not be simple.
The PC side GUI should just work, as the serial protocol will not change, assuming you get it ported over to a pic.

You will need a PIC bootloader and compiler, none of the arduino stuff will be any use to you.

Make it easy on yourself. Spend £10 on an arduino.

[h_e_c]

First of all, thanks for answering Pyrofer.

I know that buying an Arduino would be much more simpler and not very expensive. But I want to use PICAXE for two reasons: - My teacher prefers that I used PICAXE, because he likes it more and, since it is educational, I agree with him that academically it will have more value. -Since I will be provided of PICAXE chips for free, the place where I want to save money is in the ECS, not in the "core" because, like you say, it is not expensive. But an ECS costs 17 €, so I think it would not be very difficult to do one on my own using a small PICAXE.

About that last point I mentioned, I was thinking about something different. Do you think it is possible to use Arduino as the "main board" and then use PICAXEs as ECS? Or it is almost impossible to combine both? This would be a very good option, because then I don't have to port the Multiwii code.

Thanks again.

[PatrikE]

You could let the Arduino generate a PPM signal to PICAXE.
Use PICAXE to decode the PPM and handle the esc's and other external stuff like Led's and .......
It's also possible to comunicate with i2c.

I generate PPM in the MWii based Headtracker.
MultiWii_Pre4_HT.rar

/Patrik

[Pyrofer]

I picked up motor+ESC for £11 a pair.
I found ESCS for £5 and motors for £5.

If you are willing to take a risk on eBay the parts are cheap.
I assume you mean ESC not ECS? (electronic speed controller). Making your own ESC would be a nightmare.
The other option is go tiny with your quad and just use Mosfets to drive small DC motors. Check out the crazyflie.

[h_e_c]

Thanks both for answering.

I picked up motor+ESC for £11 a pair.
I found ESCS for £5 and motors for £5.

If you are willing to take a risk on eBay the parts are cheap.
I assume you mean ESC not ECS? (electronic speed controller). Making your own ESC would be a nightmare.
The other option is go tiny with your quad and just use Mosfets to drive small DC motors. Check out the crazyflie.

Referring to your answer, the money is not the main reason in the core bussiness. In the ESCs (sorry for ECSs ) the amount of money that could be saved is reasonable, so if I save that I could choose making an Hexa instead of my initial idea of the Quad. About the ESCs question, why it has to be so difficult? ESCs is only a small chip to controle analogically the speed. The only thing that worries me is the difficulty of making an analog output.

You could let the Arduino generate a PPM signal to PICAXE.
Use PICAXE to decode the PPM and handle the esc's and other external stuff like Led's and .......
It's also possible to comunicate with i2c.

I generate PPM in the MWii based Headtracker.
MultiWii_Pre4_HT.rar

/Patrik

Referring to PatrikE's answer, I did not understand you very well. Are you saying that it is possible to communicate with PPM from Arduino to PICAXE and then make the PICAXE controle things, or are you saying that I can turn a PICAXE into a ESC? The last possible answer is the one that I think you're saying, but please clarify me your answer. If it is the first one, I think it is not very useful to controle with PICAXE all, I can use the Arduino itself for that. The thing that worries me, as I said earlier, is that motor runs with analog inputs, so I don't know how I can make an analog output with PICAXE.

Thanks again.

[Pyrofer]

ESC design is not easy, its a complex 3phase output.

Take a look here http://www.rcgroups.com/forums/showthread.php?t=140454 for more details and decide if you think you can make it yourself.

For £5-£20 each per esc depending on quality not many people bother even thinking about building them.

[ronco]

Hi h_e_c.

i dont think that you can build ESC's cheaper then you can buy them.. i dont know if you know how brushless motors work and how thay need to be controlled..
i would say it isnt that easy..
.. do you have a working ESC soft for a PICAXE?

if not i would sugguest to buy some cheap ones from HK .. that will save you a lot of time and maybe also mony

regards Felix

[PatrikE]

Sorry if i wasn't clear..

Your first alternative was basicly what i meant.

You can study the code in output.pde to se how pwm signals is created in MWIi.
And google is a great source to dig in.

[h_e_c]

Thanks all for your answers.

You three are right. Making my own ESC would be nightmarish. Although I don't give up in them (because what counts is the academically effort since I'm doing a school project), I'll think in other easier alternative. For example, what about brushed motors? I've seen that everyone uses brushless ones, but a ESC for a brushed motor is quite easier than the ones for the brushless. I wonder if the control is acceptable. If it is, I would use it as a "secondary electronic configuration", so I can show it to my evaluating council. How about that? Could you give me any opinions?

Thanks and regards.

[Pyrofer]

If you make a tiny quad, <10" wide you can easily use small brushed motors and FETs to drive them.

I thought I said this before, look at the Crazyflie http://www.bitcraze.se/

This uses DC motors, it basically requires no ESC, just a FET to pulse the output to the motor.

[h_e_c]

If you make a tiny quad, <10" wide you can easily use small brushed motors and FETs to drive them.

I thought I said this before, look at the Crazyflie http://www.bitcraze.se/

This uses DC motors, it basically requires no ESC, just a FET to pulse the output to the motor.

Thanks for answering.

I'm afraid that my multicopter will be more than 24.5 cm wider (if you're referring from helix to helix). One thing that I don't understand is the FET control. The FET can be only "on" and "off", so from that I deduct that the brushed motor only works at one speed?? This seems to make no sense, please I would appreciate some explanation.

Regards.

[Pyrofer]

Google PWM.

That is how it makes different speeds for same on/off voltage.