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?
Printable View
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?
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
Blow it up! Blow it up!
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?
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.
I dont plan on trying it as I dont trust them to hold that amount of amps
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.
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
Ed, sorry off topic but are those 250g the ESC FET layer from the seventh wars?
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
Ceri - Yes.
Lots of detail here
http://www.teamstorm.com/storm2/speed.htm
doesnt that comment make this thread kinda pointless?Quote:
Originally Posted by mattsdragons
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.
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?
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!
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
https://fbcdn-sphotos-h-a.akamaihd.n...54975550_n.jpg
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
Just a quick heads up that I am working on a 150A version for some middleweights of ours.
https://fbcdn-sphotos-h-a.akamaihd.n...89196678_n.jpg
So might be possible to use it in a Heavy soon.
Steve
I'd like to know what the actual current handling capacity of these is beyond the hobbyamp figures as there is no way in hell it's actually 85A continuous. Granted I've bought a couple to play wtih and i'm sure they will be fine in a featherweight but just from their size etc I get the feeling they are around the 20 to 30 amp continuous range for 5 minutes.
even in a featherweight beefing up the heatsink is no bad thing
From the specification given for these controllers they could work if used in tandem.
The maximum voltage at 25v may be a little restrictive as many people use a little more than that.
Quote from Specifications.
1 Specification
This ESC has been flashed replaced with custom BotBitz firmware in order to allow it
to be used for brushed motors. (Brushless motors will no longer work)
ESC do not have current or temperature limiting and overcurrent and situations
will result in damage to the ESC.
1.1 Current Capacity
€ 200A burst <1s
€ 85A for 1min
€ 60A for 2min
€ 40A for 3min
For more information see the graphs in testing section.
1.2 Voltage Limit
Max Voltage 25V
Lipo: 2 - 6S
NiMh/NiCd: 5-18S
with that spec you could probably use them with wheelchair motors as most are 300w or less
Voltage is the problem, every heavyweight runs on at least 24volts (20 Nicad/Nimh Cells).
Easely enough replaced with 1 or 2 these pack. Saves a lot of weight, probably cheaper than 60 NiMH cells and accepted in heavies.Quote:
Originally Posted by blazerbotics
Other option is 4 of these.
I agree, it's a small drop in voltage, but nothing you can't solve with the right motor and gearratio. The few amps you'll draw more to compensate shouldn't make the problem.
http://www.youtube.com/watch?v=DGJjQJEdeec
I'm just gunna leave this here.
I would wonder if these ESCs would work with a heavy
are they just botbitz tz85a with heatsinks in the top picture?
It's a bit cleverer than that. They are two tz85s linked so that they work as one big speed controller. If I remember correctly they're being rated at something like 150a, which like the tz85s won't be their literal constant current handling ability but they'd take that sort of figure for quite some time.
I believe Botbitz are building middleweights to test these speedos for Robogames/Combot Cup this year, so we'll know more soon.
Link for the BotBoitz Middleweight with the dual tx85s:http://robowars.org/forum/viewtopic....er=asc&start=0
Video: http://www.youtube.com/watch?v=AA7exuzUyGo
So... I gave up on the 150A version. It looked promising and I could easily pull 500A through it but the idea of pairing up two TZ85as is inherently flawed.
It all works fine until one of the ESCs browns out. And if you happen to be using very low inductance motors, like I am, this can happen even at very low PWM duty cycle. If the motors are stalled even at low throttle this can cause the input voltage to drop very low and the ESC to reset. As there is communication between the two paired ESCs to ensure they are synced and running properly this means that if they don't reset at exactly the same time or if one powers back up first they can enter a situation where there is shoot through in the ESC causing it to blow up.
There is no way to solve this with software. It could be solved in hardware but its easier to just use a different ESC. For the middle they are 2 85As running on separate brushes. I do not know how much current is coming out of the batteries but I think it is a lot. The 8AWG wire from the batteries is too hot to touch after just a few minutes of driving. So it will be interesting to see what happens.
Steve
Good luck at the robogames Steve!
I admire your work and projects very much, the hacked brushless esc's are a genius idea, allowing people to have good and cheap esc's.
Are you saying they brown out from interference caused by the motors?
Not interference the motors draw the full amount of amps at low duty cycle for the part of the cycle they are on. (Low inductance means high rate of current change) So this means that you can have 200A then 0A in the PWM cycle rather than the motor acting as an inductor and smoothing this @ the PWM frequency.
This causes high loads on the capacitors and batteries and can cause the ESCs to brown out. (The voltage drops too low and the ESC resets) With the paired ESC I found that this happened as there was higher resistance in the 12AWG battery wires than the ESC and motor. And voltage sag got pretty bad.
This is not normally a problem as the ESC just resets and away you go again, but if they are paired. It can reset and just blow up as they are two individual controllers.
That's very interesting, testing Dan's new machine (with the TZ85s) we found th drive to be juddery and the Rx would also be flashing red (indicating it's browned out).
We plan on changing the battery to a higher spec to help the voltage drop.
How many cells were you using? I could see this happening on 2S but 3S+
It shouldn't unless you are using crappy batts or wiring.
Steve
This is on 3S, two Fan motors for drive (in a FW).
We assume it's just down to the motors overstretching the Li-Po in terms of current.
The event is over and we gave Splinter a good run, but had constant drive problems, which we partly narrowed down to the TZ85s (partly low ground clearance.)
We initially found the volt drop was dipping so low that he ESCs were resetting (causing a pause) and turning off the Rx, which would then brown out flash and cause another pause.
Solved that by putting a separate bat on the Rx, getting a bigger Li-Po (still 3S).
We then found that the drive would cut out when you gave it the beans, potentially current limiting? Limited the Tx to 50% throws, again this helped.
The final problem though was that if you put the Tx stick into the corners (diagonals, mixing on the Tx) it would cut out, every time without fail.
We also found we weren't the only ones with this problem. Tried changing Rxs, still there.
Guilherme mentioned it may be a software limitation, although I didn't fully follow. Any ideas what could be going on?
If your Tx goes beyond 100%, the TZ85 will go into fail safe.
Yes Phil is correct. Its your TX going past the failsafe limits on the ESC. I am guessing you are using a spectrum? Was both turning and forward/reverse rates limited to 50%?
What happens is that when you do mixing you get 100% on the channels when you go fully forward/backward, 100% on them when you got left/right and 125% ish when you got fully forward and to the right. (or back/left, forward/left, etc) So this can cause the ESC to failsafe if you are near these limits.
I am guessing you only limited one of the rates to 50% (prolly forward/reverse) and the other to 100% so you were still getting 100%+ in the corners.
I am also guessing this was on a spektrum radio. As this has been an issue in the past for some people but can be fixed by messing with the endpoints and rates.
I am working on a programming box to allow you to setup your ESC with the configuration you desire, this means, the endpoints, expo or linear power curves, temperature limiting, deadzone, slew rates, and a few other features. If this was my real job I would have it done by now but unfortunately its not so yeh will have to wait for that one. In the mean time this problem can be solved by reprogramming your TX.
Steve
I had the exact same problem using a DX6i. Asked for advice on quite a few forums and got nowhere. I think the problem was that the dx6i was limited in terms of how programmable it was. Therefore I've ordered a version of the hobbyking Tx and Rx system that the botbitz was designed for. Dirt cheap and fully programmable!
Thanks for the info and thorough response. I wasn't in charge of the Tx on that bot (although it was a DX6i) so don't know for sure how the throws were limited, but I'll find out.
Cheers.
It's my Dx6i.
I think there were two problems happening last weekend. Firstly my motors were really big and might have been drawing too many amps, full forward or reverse caused them to cut out. I limited them down to 50% in Mix 1 and Mix 2, not sure if that's the right way to limit them but it seemed to work as I could throw it full forward to reverse and it worked fine.
The second problem was that with the mixing on it could only go forward, backwards and turn on the spot. It wouldn't drive if the stick was moved diagonally. It may have been an amp issue but they didn't really move at all, although on occasion on wheel wouldn't move and the other would go full pelt.
Guiliherme said it was something to do with the cheap Orange RX's signal not being interpreted correctly by the ESC's. I know there were similar problems with Binky. He was running the Orange RX, Dx6i and GR02's and it wouldn't move when the stick went diagonally but when he swapped the RX out for a Specktrum AR6110 he had a full range of movement.