Team Astro Build Log (Cheese bots)

[JoeHLloyd]

Yes I know cheese is nothing to do with stars. 2 separate themes, deal with it! I thought about re-naming the team as Team Käse Chiefs or Team Fromage and In Charge or Cheesus Saves but ultimately, I like stars as well as cheese so oh well.

Thanks to everyone that helped me out sourcing electronics and materials on my first thread here: http://robotwars101.org/forum/viewtopic.php?f=1&t=2955

You guys said you like build logs so here's mine. Due to some kind of virus (has anyone else heard about this?) I seem to have a lot more time at home than I did so I'm making good progress on the design of my vert Harmesan and my friend will be printing a test chassis in PLA or nylon this week, ultimately hoping to go with carbon-infused nylon. Whilst I'm waiting for that I might as well get on top of the wiring as I expect there will be a fair amount of ****ing about with transmitter mixing and other things before it works smoothly. Still need to source some polycarbonate for the wedge and finalise the weapon disc and get it cut, but I should have a rolling chassis wired for death in a week or 2.

I drew inspiration from my 2 favourite verts - Aftershock and Cobalt. Aftershock's wheels at the back edge of the bot that allow it to back off if something gets under it (plus I'm not entirely comfortable with relying solely on weapon recoil to self-right), and Cobalt's feeder wedge strategy. In the design I've focused on making it as wide as possible to reduce gyro-dancing and as shallow as possible as I think having the wheels/turning axis closer to the weapon axis should keep manouverability high. Along those lines it's not going to be the biggest or heaviest weapon ever at ~50mm diamter - the idea is to maintain manouverability and be relentless with fast spin-up rather than delivering single knock-out hits. Cornering/manouverability is one of the vert design's biggest weaknesses and I hope to overcome that at the cost of KO power. The design is 125mm wide and 65mm deep.

Initial concept sketches


Coloured 3D model


Side profile


Not a lot of room inside


Finalised chassis


Weapon WIP and my first taste of Fusion 360

[JoeHLloyd]

Next stage of the operation I could use some help with. Am I wiring this up correctly?

The battery will be connected to the ESC only, and the ESC has only 2 wires that go to the receiver, which will power the receiver and both drive motors? I was expecting it to be worse. Also do I need to throw in one of those BEC things somewhere? I can't remember what they were for but I think I have one. Thanks for the help.

[Kyro]

having not used your brushless esc i am unsure, but it looks as though it has no bec to send power to the receiver... if your receiver can take 2s voltage (flysky fs2a? if so yes) then a bec wouldn't be necessary, however, i dont know if the esc's on the n20's support 2s voltage. so it looks like a bec may be required... or you could change your weapon esc to something with a bec (afro esc with bec for example) and you would basically just need to plug it in as is, add a switch on the positive wire and hook up everything as you mentioned...

however, if the esc's on the n20's can support 2s as well as your receiver, a bec wouldn't be required and you would get a slightly better top speed and a little more torque from a much simpler setup

[JoeHLloyd]

It says the BEC is OPTO.

I think that means it is not safe to power the receiver with it?

https://hobbyking.com/en_us/multistar-3 ... tore=en_us

Although the receiver says operating voltage of 3.5-10V, so that would presumably be OK?

https://www.banggood.com/2_4G-4CH-Mini- ... rehouse=CN

And the BBB website seems to suggest that you'll need 2s direct to receiver to get the most out of these motors:
https://shop.bristolbotbuilders.com/product/n20esc/

So does that, insanely, mean it will all work together simply?!?!

[MarkR]

"Opto" means the ESC has an opto-isolator inside (basically a LED+photodiode in the same package, the signal is transmitted optically), so the two wires coming from the RX are totally electrically isolated from the battery power coming in. This is useful, e.g. for fixed-wing aircraft which might not have the gnd of the receiver at the same potential as the negative of the esc for some reason, I guess it also helps with electrical noise. In principle they could be powered by electrically isolated batteries.

Therefore, it's necessary to connect the battery to your RX somehow, unless you use a different battery for the weapon.

If the RX cannot take the battery voltage directly (most can't ) then you will need a BEC. I think those N20s with tiny esc, can take the 8.4v of a 2S pack , but your receiver maybe can't.

It is not necessary to connect the positive wire from the receiver to the N20s, you could make a wiring loom where it is connected straight to the battery instead (bypassing the rx). The gnd and signal of course need to be connected through the rx.

Does that make sense?

[JoeHLloyd]

The RX says it's OK for operating voltages up to 10V, so I guess it's OK to wire directly to that. How do I actually supply power to this receiver then? It only seems to have 4 sets of 3 channel pins and that's it. Would I split the battery leads to go direct to the weapon ESC and to the RX?

Thanks for all the help.

[MarkR]

If the RX is fine with 10 volts, then the wiring is easy.

Just make up two "Y" cables and wire the negative and positive to the rx negative and positive and the esc negative and positive.

In receivers with traditional "servo plug" connectors, all the positive and negative pins are connected internally, so you need to wire the battery into one of them. The battery voltage will go straight back out to the motors (the n20 built-in control boards)

Power can't go into the ESC via the RX (because the opto-isolator means that even the negative / ground is isolated) so you need to run + and - both directly into your ESC.

No BEC, no problem!

[JoeHLloyd]

Great - I think I understand. Basically I should wire it up like this?

[MarkR]

Yes, that should work.

[JoeHLloyd]

It's alive! My jank soldering and hasty y-cabling has actually done the job. Had to flash the Taranis with some non-eu firmware to enable the D8 mode the rx needed. Went ahead and mixed the channels, that's all done, ready to drop into the chassis! And I'll need to re-solder a few things to cut out several miles of unnecessary wiring. But for now it will do. Might have to adjust the sensitivity curves later once I see how it drives. Briestroyer was incredibly twitchy and was in dire need of digital intervention to make it more controllable.

Only thing now - at full chat the motor doesn't sound that energetic. Is this going to be violent enough? It's a BE1806 2300kV. Thoughts?

Vid:
https://i.imgur.com/k44YDl7.mp4