What motor controller for the PI 4

Eventually, I want to build a cart to follow me around and power my 12v camp fridge. But there are so many things needed to be decided on before that (like how much beer I will need, etc). And those are discussions for another day.

I’ve decided to use Raspberry - and that seems to be the Holden/Ford debate in the sedan world, or the Toyota/Nissan debate 4wders have: they are both as good as each other, but one has to make a decision. But a decision has been made and I am happy with it. (I have an Adruino Uno but I am about to buy a Devastator Robot platform along with my Rpi 4/4gb.

Yeah, it’s a bit of a gadget/toy, but why not?

My main question is what do I use for a motor controller? I bought a Freetronics H Bridge and it works great with the Uno, but that currently has little way of being able to be controlled. You have to program all the movements into the Uno beforehand and, currently, I’m freaking out the dog.

I have an RPi of unknown origin, bought in the US by my brother-in-law as presents for my nephews. I have zero documentation and they have zero idea as to what model it is (or even how to use it to do anything……) I can’t find any reference to using the Freetronics unit with an RPi anyway.

Hence, I’m about to bite the bullet and buy RPi mentioned above and need some advice.

Can anyone help with a recommendation on a h bridge/ motor controller - preferably from Core so I can bundle it in with my purchaae and not pay excessive postage on what will end up being tiny.

Hi Peter.

Just a few thoughts of my own for you to consider.

The Devastor Robot has a load capacity of about 3Kg. A six pack of the Amber fluid weighs over 2Kg. That doesn’t leave much capacity for electronics and batteries etc. :worried:

Most motors and servos use PWM for speed control. The RPi only has 2 hardware. PWM ports, so an expansion board providing extra PWM ports is recommended. Something like this:

You could use the Freetronics motor controller with the RPi. Just check the Arduino C code from the Freetronics getting started guide with the Python code in this example and you can see how closely they marry.

So before choosing a motor driver, work out the load that is to be shifted. That will tell you what motors you need, the voltage/amperage required, and the specification for the motor driver.

That’s the easy part.

How are you going to input control info? That’s where things get complex.

1 Like

Hi Robyn,

I get fairly thirsty when I’m out in the Qld sun, so i’m not sure only 6 is going to make much difference. And then, you got to keep them cool and out of the sun.

The devastator is only the prototype/concept proof and a chance to see what I am doing is even possible. I may or might, ziptie a (closed) bottle of said liquid to the top of said alpha prototype robot in a cooler to prove to myself it can be done. This may or may not be tested in the street :slight_smile:

Ultimately, I want to scale things up and build a frame that can accommodate my 40ltr, 12v car fridge. There are a number of details to worked through for the full scale portotype yet, such as the cost effectiveness of putting 150-210mm (6-8 in) wide tracks underneath it - so that I can have my robot cart my gear to places like Moreton Island so I can pay for a walk on barge fare - $50 - as opposed to a fully fledged car return fare (circa $200!) for a days snorkelling on the Tagalooma wrecks.

Wheels would suffice for nearly everywhere else, including the fine layer of bulldust that covers the ground at the concert event called the Big Red Bash, on the edge of the Simpson Desert.

I also forsee a general use, like an extended lump from the carpark to the most remote BBQ at popular large green spaces around the burbs here in Brisbane.

And it doesn’t need to be limited to the beverages, either. You could almost bring a snack or two in the fridge. (even though, I’m reminded, “Eating is cheating”)

Also the Minister for War and Finance plays netball within 3 reasonably flat kilometres from home, and often needs shelters and camp chairs to brought down for the team, so the car fridge could be replaced with these items, as well, so that she didn’t have to drive her car - she could walk (or run) with the trolley behind her.

The plan was to not only have a 2 channel radio control, similar to your basic RC Car, so you can move it with fine control, but I was looking at being extra fancy and try to have it follow some kind of rf beacon - either a simple radio setup, WiFi or Bluetooth based, or even GPS receivers both ends.

There are so many unknowns with this full scale project that I have to build a base robot to see if the technical stuff works and is feasible, and that’s where the Devastator comes in.

It could turn out to be cost-prohibitive to buy the motors or batteries for the full scale unit. The tracks are likely to cost me US$3-5K fully assembled but there’s always the wheeled option. (Which limits me to where I can take the bot)

So, yeah, the Devastator may not carry a 6-pack, but the devastator is just the beginning! :smiley:

I can see where you’re coming from @PeterMiddo

As a boy from the tropics myself, I know what the hot sun is like.

Have a look at the APM rover project. I think this is close to your desired end result.


Very close @Robin57159, except I more or less wanted it to follow along behind me at a distance of 2-3 metres (under the assumption that nothing gets within about 500mm as a safety margin)

But you are correct and I will now follow along very closely.