Problem; Scorpion XL going spaz!

[stu]

Problem; Scorpion XL going spaz!

Yeah one terminal in the EVs is connected to the motor casing which in turn bolts to my metal chassis shorting the motor outputs together.

This was a major problem with Rexs Robot Challenge with people using wiper motors.. yes they were being taught to use in wooden bots.. but soon as they started making thin metal chasiss they didnt understand why the speedos were blowing.

Dissconnect one motor and test, then connect other motor and then problem appears. Thats how i found it out. Even Chis from Robot Power was like wow cool fault finder that the Robot Power Software is very smart.

Mr Stu

[glen]

Problem; Scorpion XL going spaz!

dont want to start a whole new thread for it so ill ask here,

got a new spinner bot with a brushless motor and 6 a123 cells powering it all with a scorpion XXL on the drive. i had troubles to start with with the BEC not being enough and causing the weapon to jam on and lock everything up. not good.

using a S-BEC now and disabled the on board BEC which has fixed that but now while the weapon is spinning up initially for about 3 seconds, it causes the voltage to drop to about 15v for 3 seconds which makes the status light go out on the scorpion and no response from it until the voltage picks up and it works great again.

so it seems like the voltage bounced between 21 or so and 15 which is either side of the 16v they recommend you cut the HV jumper at.

question is - what does the HV jumper control? have a suspicion it is something to do with the 5v regulator so now im using a bec i was contemplating just rejoining it and seeing if it works better with the voltage drop.

the controller should work okay through the drop as its rated down to 4.5v but yeah i think the HV setting is causing it problems.

any ideas on what i could do here? no ones seemed to have this problem in australia quite yet.. and you guys seem to use the controllers a fair bit

aside from that the XXL is going great!

cheers guys

[woody]

Problem; Scorpion XL going spaz!

Got a decent pair of 12v SLAs or similar kicking around that you could temporarily lash up to the controller just to confirm that voltage drop IS the problem?

6v seems an excessive drop...So Id suspect that one or more of your cells is duff.... or you could add in one more cell.

[woody]

Problem; Scorpion XL going spaz!

Note that Ive tried the XXL on 8 A123 Cells ( 2 off 4 cell packs ) without encountering any magic smoke AND had much the same problem as yourself with a homemade pack in which Id fudged two cells .. they appeared to charge fine but under load their capacity to supply was greatly reduced.

So ..Probe each individual cell rather than looking at the pack voltage.

[razerdave]

Problem; Scorpion XL going spaz!

Hey Guys

if the power to the receiver runs through all of the RC cables, why would you need a BEC lead in the first place ? and wouldnt 3 lots of whatever the BEC is producing do harm to the RX ?

Im getting a seperate BEC so I can run my gyro and switcher as well, but just to get some confusion out of my head...

[woody]

Problem; Scorpion XL going spaz!

David ...All the positive pins in the receiver are attached to a single rail....the same applies to the negative pins they are all connected to one internal rail.

[razerdave]

Problem; Scorpion XL going spaz!

I presume that they are connected in Paralell along the rail, not series ? and as I said, if the other 2 are already providing power to the RX via their respective pins, whats the point of the BEC function ?

Sorry, I may just sound thick

[typhoon_driver]

Problem; Scorpion XL going spaz!

yes they are paralleled.

Well it would give you more current for those power hungry spektrum receivers and RC relays etc but in the magical world of electronics which I dont really understand it can cause problems.

[widow_twanky]

Problem; Scorpion XL going spaz!

If the internal BEC is rated at 100mA and the receiver draws 130mA then theres not enough power.

100mA delivered down three wires will draw 33.333mA on each wire (if theyre the same resistance. It doesnt matter how you connect them to the receiver youll get the same.

With the spektrums your receiver will probably cut out if you dont use a seperate BEC which delivers a bit more power and has a capacitor to smooth out the voltage.

For smoothing out dips in voltage due to motor starting etc you can stick a capacitor in and that sorts it out. A seperate BEC has a seperate power supply to the capacitor which means it can deliver more power. The ones we use (thanks Geoff - http://www.technobots.co.uk/Data Sheets/1062-010.pdfhttp://www.technobots.co.uk/Data Sheets/1062-010.pdf) can deliver 1.5A.

Dave, the best way i can describe it is that voltage will relate directly to pressure in a water system. If you have three wires at the same voltage/pressure, the voltage/pressure is unaffected (ie: an equilibriam is formed).

Current is available but if not used it doesnt flow.

Its actually described a lot better in my 1903 version of the electrical educator (how sad do you want me to get?). The older text books use the terms pressure and flow for voltage and current which I found useful.

Andy

[mightymouse]

Problem; Scorpion XL going spaz!

Back to Glenss question, the 6v drop is probably caused by the brushless motor - which draws a huge amount of current at zero revs. I had a similar problem with Velocirippa as the drive motors were switched by dc contactors, the current draw was sufficient to prevent any other circuits from working. In many fights the steering would stop working but functioned perfectly on the bench - the problem was solved by fitting another battery pack to run the ancilliary systems and have the main battery pack working only the motors.

Trev

[woody]

Problem; Scorpion XL going spaz!

Lets try again.....if the power to the receiver runs through all of the RC cables

It may appear ...as in the case of the XL and XXL controllers ... that a seperate power supply runs thru ALL of the R/C connections but you should consider it as ONE power connection TO the Reciever....you can indeed have just ONE complete plug and remove the positive and negative from the others.

Any help?

[razerdave]

Problem; Scorpion XL going spaz!

that I understood I beleive I should invest in a seperate BEC because of the very low current delivered by the XXL, as I have to power a gyro and gyro switcher off it now. I presume I should cut the BEC link on the XXL before installing the seperate BEC device that andy/geoff suggested ?

[widow_twanky]

Problem; Scorpion XL going spaz!

Depends on what the instructions say. Dont think we cut it as the Dimension engineering ones can be fitted in line. That said, things change, so read the book its not very big.

For some reason when we put the BEC on the Scorpion XL on Cylon it didnt work. Plugging it into a seperate port worked.

One other thing, I have found that when using the Scorpion Minis, because its TWO controllers and TWO BECs we didnt need a seperate BEC.

Andy

PS: Thats actuall what I was trying to say Woody, obviously not very well!!

[grant_ploughbot]

Problem; Scorpion XL going spaz!

Glen, sounds like your plling way too much current from those cells on start-up. If i recall correctly your running a pretty powerfull motor on that spinner, and A123s will only discharge about 70A peak. Under start-up loads i would expect your motor to be drawing far far more than that. If Its drawing so much without the disc attached, i would deffinatly look at running an extra set of cells in there.

[glen]

Problem; Scorpion XL going spaz!

yes it definitely is drawing too much power you can see the disk speed dipping alot when you drive it around but for now itll have to do till i can get a big lipoly for it,

but about the problem after talking to chris baron - i ran the SBEC with the BEC jumper attached on the scorpion and have removed the onboard regulator on the xxl (just lifted the outside leg on it)

problem is solved!