Monsterborg questions

Submitted by stevem on Tue, 05/23/2017 - 20:14

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Hi Folks,

I'm considering pre-ordering a Monstorborg, and I had a few questions. I'm a bit of a noob with this stuff, so please forgive me if this info is available elsewhere on your webiste -- I looked for quite a while, but I couldn't find definitive answers. Anyway, here goes:

1) I'm wondering what the suggested method(s) is for keeping the rover driving in a straight line (I'm thinking about autonomous use). Obviously some type of feedback would be needed, and I would guess that encoders on one or more wheels would be a good start. It didn't seem like these were included, so I was wondering if they _are_ included or could be added on. Maybe there are other ways as well? Likely _not_ GPS as I can't see GPS giving the necessary resolution, particularly over short distances (plus it would likely have trouble indoors).

2) Since the Monsterborg only comes with 1 Thunderborg controller, I'm guessing that 2 motors are connected in parallel for each Thunderborg driver (i.e., 2 sets of 2 motors in parallel equals 4 motors). Correct?

Thanks for the help,
Steve

piborg's picture

piborg

Wed, 05/24/2017 - 11:13

Hi Steve,

There are no encoders or motion sensors with the MonsterBorg as standard. You could try and find an encoder which would fit somewhere inside the wheel, or you could fit some other sensor which picks up the wheel rotating. Alternatively you could try using an accelerometer / IMU to measure the motion of the robot, sideways movement would mean you are not driving straight.

You are right about the connections: both right-side motors are attached in parallel to M1, both left-side motors are attached in parallel to M2.

Most of our autonomous code has focused more on using the camera to navigate so far. In that case driving perfectly straight is less important as you are trying to follow a path or object which may or may not be stationary. If you take a look at our Formula Pi image processing blog posts you can get an idea of the sort of processing we are using to drive around a track :)

stevem

Wed, 05/24/2017 - 14:35

Hi PiBorg,

OK, thanks for the quick response! I didn't think about using the Raspberry Pi camera, this sounds like a good option to consider. I'll have a look at the blog posts.

Steve

cnobile2017

Thu, 06/15/2017 - 13:19

Is there space for an additional Thunderborg controller? Without a controller for each motor, steering would be more difficult and less precise. Also, I was thinking of using four 18650 Li-Ion batteries connected in series (~14.4 volts), would there be enough space for these batteries also? I'm currently designing a discharge protection circuit for the Li-Ion batteries.

Thanks, Carl

piborg's picture

piborg

Thu, 06/15/2017 - 15:21

Hi Carl,

There is probably not enough space under the MonsterBorg to fit a second ThunderBorg, however it should not be necessary.

The ThunderBorg is designed to handle rather large motors, the motors we are using on MonsterBorg are small enough that each of the outputs on the ThunderBorg can easily handle the output to two at a time :)

The steering from a standard MonsterBorg is rather responsive and in our tests the human was the limiting factor for precision:

As for batteries I am sure you could fit four of the 18650 sized batteries in place of the 10x AA holder. The body of the holder is 29 x 59 x 75 mm, the 18650s are 16 mm diameter and 65 mm length. You can wire the batteries to either the 9V style connectors, or directly into the V+ and GND screw terminals on the ThunderBorg itself.

If you do use Li-ion / LiPo batteries we would suggest a protection circuit like you have mentioned. it might also be worth looking at some kind of protective case or barrier to prevent things like stones from damaging the batteries as well.

cnobile2017

Thu, 06/15/2017 - 20:30

A four battery case is 80cm x 76cm x 20cm this will probably be too large. If I use two double battery cases it would be about 40cm x 76cm x 40cm also too large. Humm, I may need to wait till the bot shows up at my door before making any design decisions on these batteries. BTW--The 18650 cells are the same ones used in most laptop computer. I got four good ones from an old battery pack and bought four others so I could switch them out. I'll be charging them in a stand alone charger.

Thanks for the quick feedback--Carl

ken.cook859@gma...

Thu, 06/15/2017 - 23:51

Does an RPi 0 W have enough capability to run the monsterborg properly? Or do you need to use RPi 3?

piborg's picture

piborg

Fri, 06/16/2017 - 11:22

MonsterBorg should work fine with the Pi Zero W, but you will be down on processing grunt.

If you want to use MonsterBorg primarily for joystick (RC) based control or from a network based access like our Web UI then everything should work nicely.

If you want to run autonomous code or performing image processing of some kind then the Pi Zero will limit how many images the robot can handle each second, reducing performance significantly.

Put simply if you are intending your MonsterBorg to drive itself I would strongly recommend a Raspberry Pi 3 instead. If you want to drive it yourself from a controller or via the WiFi then a Pi Zero W should work just fine :)

AlexFielder

Thu, 07/06/2017 - 12:24

Hi all,

I just filled out my Kickstarter survey so am interested in how I can actually control the thing when it arrives?

All suggestions welcome!

Thanks,

Alex.

EDIT: So it looks as though I can use a Bluetooth-capable controller to talk to the Pi, that'll teach me for posting first without searching.

This page seems like it will work: https://www.piborg.org/joyborg

My next question is this: I have an old Ouya (remember that?) controller which has Bluetooth, can I use it to control the MonsterBorg? I guess it really hinges on the Pi recognising it once it connects, right?

piborg's picture

piborg

Thu, 07/06/2017 - 13:18

The full code examples will be up on the website soon, but there are some bits already available.

For Joystick and programmed sequences the standard ThunderBorg Examples should work. All you need to do for a Bluetooth joystick or gamepad is get it synced with the Raspberry Pi :)

The joystick example should work with most controllers. You will probably need to change the settings as they are correct for a PS3 controller by default.

We have also added MonsterBorg to our Web UI code on GitHub. This allows you to control your MonsterBorg remotely via a phone or web browser.

AlexFielder

Thu, 07/06/2017 - 13:23

That looks really cool. **Wonders if the MonsterBorg could be used for transportation of beer from fridge to chair...** "sudo bring me a beer". lol

Thanks!

cnobile2017

Mon, 07/17/2017 - 03:24

What is the current drawn from the batteries? I assume it would be a nominal value and some sort of peek value.

BTW--The Li-Ion battery protection circuit that I'm building is on my GitHub account. https://github.com/cnobile2012/Li-IonBatteryProtection. I have the circuit built, but I'm still testing it, so far no smoke. The board is kind of big, so I'm not so sure where it will fit till I get the MonsterBorg in the door.

Thanks!

piborg's picture

piborg

Mon, 07/17/2017 - 11:25

It will really depend on how the MonsterBorg is driving around.

Completely idle (no movement) the big power usage will be from powering the Raspberry Pi and any connected USB / GPIO devices. Depending on how much work the Raspberry Pi is doing and which model you use. Personally I would suggest this could be anything from about 30 mA for an idle Pi Zero up to about 200 mA for a Pi 3 running at full load.

When moving the motors will be the largest draw, faster speeds and changing speed rapidly will need the most power in this case. As a rough idea we tested a MonsterBorg driving around our Formula Pi track and recorded a runtime of 3 hours and 8 minutes from a pack of 2700 mAh batteries. This works out as an average of about 860 mA for driving at full speed without too much braking / accelerating and driving.

For hard work such as changing direction constantly or driving up hill you should allow more current. We have not measured but at a guess I would say allow twice as much for hard work and even more for instantaneous spikes when under hard acceleration or braking.

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