Reliable High Discharge Lipos

[grant_ploughbot]

Re: Reliable High Discharge Lipos

Sounds like you've got it all planned Craig
I have no idea how reliable or how well the gimson drill motor's work on 20v, but i remember Ewan saying he doesn't confirm they wont burn up at that!
The fan idea is quite a nice one, infact one that john reid has tried out for beta before. I don't know if it was just the sheer size and force he needed but john found it wasn't really possible to get the downforce needed as there were so many losses just to spin the fan up. Would be nice if you could get one to work!

[grant_ploughbot]

Re: Reliable High Discharge Lipos

Whats the power of those 550 motors ewan?

[harry hills]

Re: Reliable High Discharge Lipos

i have fitted my GR01 gearboxes with some 12v motors and am overvolting them to 18v using 75mm wheels, should be pretty fast

[ewan]

Re: Reliable High Discharge Lipos

Power information is here http://www.gimsonrobotics.co.uk/GR01_pl ... tions.html

With over-volted 550 motors overheating can be an issue because it's all got to go through such a small package, hence why heat-sinking and ensuring good airflow about the brushes at the rear is pretty much essential for >50% voltage increases. You can still get away with it due to the quite monstrous torque of a set-up using 36:1 drill-type gearboxes with wheels a reasonable size (<120mm). In most cases you're going to be running only just past the peak efficiency point of the motors to reach wheel-spin - it's usually only when you get too far past this point by running excessively large wheels or trying to run with a jammed wheel that motors will fail.

Using this 50% voltage increases. You can still get away with it due to the quite monstrous torque of a set-up using 36:1 drill-type gearboxes with wheels a reasonable size (<120mm). In most cases you're going to be running only just past the peak efficiency point of the motors to reach wheel-spin - it's usually only when you get too far past this point by running excessively large wheels or trying to run with a jammed wheel that motors will fail.

[grant_ploughbot]

Re: Reliable High Discharge Lipos

That's a nice little calculator actually - although for the current draw it's abit optimistic! using astro's it say's i'll never get over 21A, but i know for a fact its pulling WAY more than that changing direction (peaks of 100A I can get easily)! Not seen that before, looks useful!

[craig_colliass]

Re: Reliable High Discharge Lipos

Hi

John did use a fan system for Beta but found the losses of the drive too much the other problem he had was the robot sucked the arena floor up! But this didn't stop him sticking the robot to the Garage door or something like that.
A feather should be OK. You could use a standard ducted fan with about 1000 grams thrust. if the unit was shock mounted it should be OK.
The Gimson motors are rated at 14.4v I think, add 50% to this and I make it just over 20v I don't like over volting things like motors personally as they tend to brake more frequently but everyone here is into POWER :shock: I would add Tron works well as a pusher with four 9.6v drill motors running at about 12v.
I don't think I would make this robot as it doesn't interest me enough I would like to make a fighting walker featherweight next

[grant_ploughbot]

Re: Reliable High Discharge Lipos

John had a fan system working for killerhurtz that worked OK, although the astroflights burnt out quickly. The newer brushless version to give 400kg of downforce took over 1kw just to turn the belt!
As you say, things get abit trickier when going for extreme power and lightweight parts

[mattsdragons]

Re: Reliable High Discharge Lipos

do you use brushless drive in ploughbot grant?

[Mouldy]

Re: Reliable High Discharge Lipos

Missed this thread, ill try answer some key points;

Lipo - ive gone of flightpower- delivery/customer support sucks, thunderpower seem consistantly good, id suggest buying through fastlad.co.uk, there really good, there other brands are also good.

Wheel grip- i used shore 50- 80mm od, 6 of them, all 25mm wide, with the magnet, other robots didnt stand much of a chance... i couldnt physically push it sidewards once it was on some steel sheet.

my gearbox's broke because i used bad quality gears, welding made them brittle, and the geometry was bad- tiny pinion on a large 2nd gear... the angle of the teeth just wore them out real fast...or just snaped the teeth off, gearbox's had no flex. Just bad design on my part.

motors;

Dewalt powerdrive kits - good in low gear, real powerful, but with an 80mm wheel it was a tad slow for my liking... but it could of driven all day long with the magnet in without getting hot, in high gear.... fire.

Speed 900's... would of been fine if the gearbox's were beefed up, with 9:1 on the 80mm wheels.... but with the magnet in.... more fire

If i was to do it all again and try to make the best fw pusher.... id probably look into sensored brushless.

[grant_ploughbot]

Re: Reliable High Discharge Lipos

No I use astroflight 940 brushed motor's. they're about $450 each now, certainly not cheap!
I would be tempted in the future to look at the sensored brushless motor's, but at the moment I dont see any point. I've got an ultra lightweight system at the moment and the high end brushed ESC's such as the mini vantec I have the best control by far. I can't see the brushless ESC's being as nice to control as these. I have more power than I ever need in these motor's so untill I run out of them (which I've burnt out 4 in satans mutt already on the disc ) i'll stick with these.

[Eventorizon]

Re: Reliable High Discharge Lipos

I thought you could not reverse a Brushless motor?

I have talked it through with my dad, its going to be his machine after all, and it seems that its speed 900 drives, with a speed 900 drum on the front, but what voltage can we gat away with?

The voltage range of a Speed 900 is 6-40V so what would happen if we ran all 3 speed 900's off a 10 Cell lipo, with victor 885's for the drive and a simple relay for the disc. or is using 10 cells a little mad.

The only thing is that until we know the voltage we cant get the speed of the motor and from that work out the gear ratio, I think we are sticking to the 40 shore Banebots 124mm wheels, 6 of them

[grant_ploughbot]

Re: Reliable High Discharge Lipos

You should be fine running a 6s lipo in there, I'd probably go with a 5000mA pack so that there's plenty of power available and you wont be stressing it so much. Its only about 700g aswel

[PJ-27]

Re: Reliable High Discharge Lipos

which I've burnt out 4 in satans mutt already on the disc

What burnt them out? Does no one else find it odd that $450 motor just burns out, especially on a robot that (as far as I'm aware) is seldom used?

The amount of people that had problems with Speed900s at the UK champs this year, which at £50 each I would have expected more, but $450!

It all seems so fragile in an application that's so intense.

[Ellis]

Re: Reliable High Discharge Lipos

I believe he burnt two out at the Yeovil event. If I remember right, the mounts came loose? Something like that anyway. Not (technically) the motor's fault.

As for the money involved, I can't quite get my head around it either! We felt pretty sorry for ourselves when our 15a Electronize (~£30) died.

[ewan]

Re: Reliable High Discharge Lipos

I burnt out an Astroflight once, really not that hard to do- just put it under a particularly heavy load for too long (or stall for a bit) and the amount of current going through it will heat it up very quickly indeed. A stalled motor DC motor acts pretty much like a heater so the heat energy produced = I^2 x R and if its small like an Astroflight there's very little thermal mass for the heat to escape to so it quickly turns to magic smoke. It's nothing to do with how 'well' the motor is built, it's just the type of build (small yet powerful) and the ridiculous loads we put them under that kills them