Botbitz 85a esc..... in a heavy?

[mattsdragons]

Just wondering if anyone has yet to have tried them in a heavy?

In theory they should be fine as sidewinders can hold 80a and they are used (though rare) so could be a low cost esc as long as you change wire to handle the current?

[maddox10]

Re: Botbitz 85a esc..... in a heavy?

I think, with 4 used on 12V-16V, with 4 Bosch 400's or simular, gig gearratio and low end speed that it should be possible.

But, I don't know how they will handle the real speedo-killer, the braking energy.

Maybe worth a test

[psychostorm]

Re: Botbitz 85a esc..... in a heavy?

Blow it up! Blow it up!

[mattsdragons]

Re: Botbitz 85a esc..... in a heavy?

Why would it blow up?

Bad example but 4QD NCC70's, 70a esc and they are fine on 750's, if the starts are true, why would the 85a botbitz blow?

[blazerbotics]

Re: Botbitz 85a esc..... in a heavy?

this says it will do 320amps and its only 6quid http://www.ebay.co.uk/itm/320A-Speed-Br ... 35bef558e3 ! Its all down to how the manufacturer rates the controller. everybody seems to be jumping to reccomend the BB controllers, yet i don't know many people running them. Feel free to try them, but don't expect them to last long.

[mattsdragons]

Re: Botbitz 85a esc..... in a heavy?

I dont plan on trying it as I dont trust them to hold that amount of amps

[maddox10]

Re: Botbitz 85a esc..... in a heavy?

size, heat dissipation, overstated capacity.

An NCC70 relies on simple relais to switch directions, and the single mosfet bank to control the power is mountend open on the heavely coppered PCB.

The TZ85's are Chinese build el cheapo speedo's for brushless motors, reprogrammed to act as a Hbridge speedo. All the power flows trough 1 chip with 6 mosfet banks baked in. Only 4 of those banks are used.

Reversing a Bosch 750 in a heavy from nominal draw means coming from 24V 40A to stall -24V 200A+ and back to 24V 40A inside milliseconds. This gets worst if the reversing is done when stalling or accelerating.

I think you see the potentials for magic smoke.

It's also the reason I wrote Big gear ratio and low top speed. This will lower the draw of amps.

[teamstorm]

Re: Botbitz 85a esc..... in a heavy?

I would expect an epic fail from this, for one simple reason..... the thing that kills FET's is heat. Yes it might be the current that generates the heat, but getting heat away from the FET's is key to keeping a controller running. Thermal mass is everything !

The 4QD NCC-70 had a large lump of aluminium on which the FET's were mounted, which in turn people tended to then fix to their chassis - creating a large heatsink, and as Mario says, by using relays to switch the direction of the bridge, more stresses on the FET's are avoided. The 4QD NCC-70 is now rebadged as the VTX http://www.4qd.co.uk/prod/vtx.html but you can still see the FETs mounted to a large block of aluminium.

Even the good old Sidewinder had a decent thermal mass (the ability to absorb heat away from the FETs) and spread that energy through a number of FETs which in turn spreads out the heat.

You'll notice most light weight speed controllers that don't have thermal mass rely on active cooling (the Victor IFI for example has no heatsink and a fan) - my view is that's not the way to go, I don't want my robot not blowing up to rely on some flimsy bits of plastic whizzing around.

My advice, for a heavyweight, unless you SERIOUSLY know what you're doing, and have pots of money to play with, stick for something proven - you don't want to be playing at experiments

This speed controller weighs 60g - to give that some context the FETs alone in Storm II's original controller weighed 250g !

Conclusion, no thermal mass, not built for the kind of high-current breaking that robot motors do throughout a fight = FAIL

[psychostorm]

Re: Botbitz 85a esc..... in a heavy?

Ed, sorry off topic but are those 250g the ESC FET layer from the seventh wars?

[mattsdragons]

Re: Botbitz 85a esc..... in a heavy?

Thats exactly my thoughts, I wouldnt trust them at all for a heavy just due to their size etc. Im not stating for one second that I personally would use them

They say that they can hold 85a true current but I wouldnt use them, got my Roboteq which does me quite nicely

[teamstorm]

Re: Botbitz 85a esc..... in a heavy?

Ceri - Yes.

Lots of detail here

http://www.teamstorm.com/storm2/speed.htm

[Mouldy]

Re: Botbitz 85a esc..... in a heavy?

They say that they can hold 85a true current but I wouldnt use them, got my Roboteq which does me quite nicely

doesnt that comment make this thread kinda pointless?

I've been impressed with the botbitz escs... use them in diablo without fault on some 500 size whyachi drives, and in 720 on the 700size motors, i blew a motor and the esc was still fine... if a tad warm.

I think a tz85 would run a bosch 750 powered heavyweight.... maybe not for very long though as Ed said- the heat would melt it... the fets are lightly pressed against a heatsink with a bit of compound to transfer heat.. in the big esc's the fets are bolted to a heatsink- much more positive.

However i'd like to see if someone could hack something like the castle ice 200a, capable of up to 300a with current limiting....but then before hacking there £200 isn x 2 = £400 ish... plus all the development time etc... just buy a wotty.

[typhoon_driver]

Re: Botbitz 85a esc..... in a heavy?

So what would be the issue in bolting the esc to a large lump of metal in the bot and making sure the fets are well connected to it?

[PJ-27]

Re: Botbitz 85a esc..... in a heavy?

There's always another weak link.....

@ Dave, How did you manage to blow a 700 size motor? Honey Badger hasn't even been in a fight yet!

[marto]

Re: Botbitz 85a esc..... in a heavy?

I wouldn't recommend them in a heavy, but that being said if your drive train is very tame then maybe...

Check out the graphs here.
http://www.botbitz.com/manuals/TZ85A_Manual.pdf

Of course the will never do 85A indefinitely but its really a question of how long you NEED to pull 85A for.

BTW these tests were conducted @ 12V most bots run considerably higher voltages which means more power running through the ESC which will contribute to the heat. Keep in mind this is a $65 controller, which was intended for featherweights.

And I did this to it


Yes those are clamps.

I have worked out a way to pair 2 x TZ85as together to make a custom ESC. Aim is to use it in a pair of middleweights at some point in the future. 3x increase in FETs and will have custom heatsink. If it ever gets built you may be able to have your Heavy Hacked Hobbyking ESC.

For updates on our dev we are most active @ www.facebook.com/botbitz

Steve