Build Diary and some questions that may appear - BW/MW

[Merkabah_PT]

Re: Build Diary and some questions that may appear - BW/MW

Body build day 3:
Now this is starting to look like a combat robot!








(Don't mind the sandwich, working makes me hungry )

Today i also ordered my radio system, a FlySky CT6B 2.4Ghz 6-Channel Transmitter+Receiver, and a bunch of Deans Ultra Plugs (60‚/£50 with registered shipping).
(review some guy made)
http://www.youtube.com/watch?v=BbjfC2ecWt8



Cheers!

[Merkabah_PT]

Re: Build Diary and some questions that may appear - BW/MW

I received my package today, just 1 day after making the order!

6ch 2,4Ghz FlySky Radio System, 5 Deans Ultra Plugs and some Futaba connectors.









I haven't tested the radio because i will buy the batteries support this afternoon.

Yesterday i worked a little more on the robot body, i made 2 axel supports and added 1 triangle on each side so the robot doesn't get stuck if it lands on its side.




Later today i will update this build diary again.

Cya later! :wink:

[Merkabah_PT]

Re: Build Diary and some questions that may appear - BW/MW

Radio system tested and every thing appears to be good, still have to try the software to program the TX from the computer (elevon mixing to control the robot with just one stick).

I also finished building the H-Bridges, they don't look very good but they work great. I have to find a small plastic box to put them in.

(The two relays at the right are old ones, 5/6 years old, i was a kid and didn't know how to properly solder )







Small video of the first test drive (my smartphone sucks at filming...).


The robot is much faster than i tought it would be. It's running at 6V at the moment, but i might use a 7.2V battery because my cells haven't been used for 5/6 years and they don't hold the charge (1/1:30minutes of use and they go empty).

The robot weights around 2.2kg with the batteries and all the electronics. It can't be a beetle but i will make it an mantisweight with active weapon. Now i can because of the 6ch radio. But i will leave that for a near future, now i have to save money to buy two 6/7.2V batteries and a proper charger.

I have a 550 motor from a broken 12/18V drill, i am thinking of using it to power a vertical spinning bar/disk.
Maybe something like this:

(I know the disk teeth are wrong )

Cya.

[Merkabah_PT]

Re: Build Diary and some questions that may appear - BW/MW

So, i forgot that i should put a protective diode on my relays coils to protect the servo pcb/receiver.
My circuits look like these, how should i install the diodes? Any help? I don't want to destroy my receiver.


(It was drawn very quickly on paint)

[daliad100]

Re: Build Diary and some questions that may appear - BW/MW

Reverse bias parallel to the coils (backwards across the coils)

[Merkabah_PT]

Re: Build Diary and some questions that may appear - BW/MW

Like this?



The two relays are connect to a servo pcb, instead of the servo motor, and the two wires change polarity. Will the pcb/receiver be protected this way?

I have seen some people from RC forums doing this exact same schematic (without the protection diodes on the coils) without any problems. May be the protection diode only works/is requiered when using microprocessors and such? I don't see how the diode will protect the pcb on a changing polarity circuit like this...

[Merkabah_PT]

Re: Build Diary and some questions that may appear - BW/MW

Tomorrow my 7.2v 1800mah battery should arrive, so i am checking my wiring. Currently its done with 22awg (0.644mm) wire, but it looks to thin for me. I was thinking of replacing all the wires with 18awg (1.024mm) i have.
Holding the wheel on the motors they pull about 10A each, will wiring be fine with the 22awg or should i really replace with 18awg?

Every thing i find on the web is different from site to site, some say 22awg only handles 1A, other say it handles 7A others say it handles around 14A.

You guys have personal experience, so i am asking you.

[Bodge Job]

Re: Build Diary and some questions that may appear - BW/MW

i use something overly thick (after all my wiring melted at an event) , i use 2 mm wire (i dont know the gauge) but if its only 10 amps, the 1mm would probably do as its a lighter weight robot

[Merkabah_PT]

Re: Build Diary and some questions that may appear - BW/MW

So, today my new battery should have arrived, but the mailman didn't ring my appartement bell and forgot to leave the warning for me to withdraw my package at the postoffice. Tommorow morning i will go to the postoffice with my delivery code and try to withdraw it, but i expect it to be a pain in the a**, as portuguese workers tend to over complicate things...

Today i replaced the wiring with 18awg just to be shure nothing melts and couses a short-circuit. Better off this way.

My build it on standby until i get my battery, and 3 days doing nothing is killing me.

After this first fase of building Primogenito as a wedge robot, i will have to save some money to get 2 pulleys, a belt and a 12v battery to power the weapon (vertical spinning bar). After that i will start to design and build the upgrade so i can have some fun with the robot destroying things.

Cheers.

[Merkabah_PT]

Re: Build Diary and some questions that may appear - BW/MW

Phase one at 95%!

Primogenito is as compact as it could be, it was almost impossible to fit the receiver batteries. I am considering making a BEC so i only use the main battery and it's much smaller than 4AA batteries. What amperage you guys think i should chose on a voltage regulater to build the BEC? 1, 2 or 3amps?

Just need to make the main battery removable link, program the elevon mising and sand/paint the steel bottom and wedge (their surface is rusting pretty bad).

My father showed me a trick to remove rust using lemon juice, but i will sand the metal so that the paint will adhere better.

I was going to make a small test drive video, but batteries only come with a little charge and it died on me...
I will leave you with some photos (this time they were taken with a digital camera ):

[Eventorizon]

Re: Build Diary and some questions that may appear - BW/MW

Just buy a BEC, the are only £15 or so and will be much more reliable than a custom one.

Great machine though. Very, very tight!

[Merkabah_PT]

Re: Build Diary and some questions that may appear - BW/MW

Thank you for the compliment, that really means alot to me! This is my first real robot following rules. I have built others when i was younger but they were mostly abominations made out of scraps.

I will not be competing, so this robot will be more like a expensive home made toy. But when i have the money, i will have to order a batttery to power the weapon i intend to add, so i might follow your advise and add a UBEC to the order, just 7.5‚ (£6.5).

Atleast if the chance to compete some day appears, i will already have most of the gear.

[Merkabah_PT]

Re: Build Diary and some questions that may appear - BW/MW

After 1 hour of searching for the drivers of the programming cable for Win7 x64 and tinkering with T6Config, i finnaly got my mixing working right.

I was so happy that i started to chase my dog through the house to get used to drive with one stick. The robot was really really nippy, but the speed started to drop fast, and after 2 or so minutes the robot barely moved.

I have to wait until 6 in the afternoon to get my multimeter back and check power consumption, but my motors stall at around 10A, so worst case the two sould draw 20A. By my calculations i got this:

Battery outputs 1.8A for 60minutes
Motors draw 20A (worst case scenario)
20A is greatter than 1.8 12 times
Battery duration will be 12 times less
60/12=5
Even with the two motors stalled, the baterry should last 5 minutes.

So, i thought that the problem should be that the battery wasn't fully charged.

My baterry is a 7.2v 1800mah ni-cd pack and my charger outputs 1000mah, so i use this formula e saw on many RC forums to calculate charging time:

1.4 x (baterry mah's) / (charger ma's) = charging time in hours

1.4x1800/1000=2.51

2h30minutes of charging time.

Is this correct or should i leave it charging more time?

[Bodge Job]

Re: Build Diary and some questions that may appear - BW/MW

i would charge it a lower current for longer, the higher the current the less the battery absorbs, and depending on the quality of the battery it may require event longer, i would sugests trying it at half that current if you can, but if your charge cant do this, then you may have to try and get a better charger. cycle charging may also help (discharge it completely at a low current, and then charge it up again at a low current.

NiCds also have a memory issue, so before most charges (when you can) try and discharge them first.

[Merkabah_PT]

Re: Build Diary and some questions that may appear - BW/MW

Thanks for the reply Alexander.

I have read, as you say, that charging at lower current is better. I only have this chager, and can't afford a good/proper one.
This one was bought along with the baterry pack, and the guy from the webstore told me it was completely compatible. But to me, it looks like a regular AC to DC converter, not a real charger.

It has a led on top, if i connect the charger to a outlet the led lights green, but when i connect the baterry it turns red. I have sent an e-mail to the store to ask if the led turns green when the charging is done, but they haven't answered yet.

The battery is charging right now (started at 15:00), i will wait 3 hours (18:00) to see if the turns green. If it doesn't i will wait one more hour and then disconnect no matter the result.

Then i will do some test:
-start a chronometer and run the robot until it dies;
-use the multimeter to see how many amps the motors draw while driving around.

Just for reference, what battery amperage people usualy use on feathers with two drill motors?