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

[marto]

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

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.

[PJ-27]

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

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.

[marto]

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

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

[PJ-27]

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

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.

[PJ-27]

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?

[Phil]

If your Tx goes beyond 100%, the TZ85 will go into fail safe.

[marto]

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

[Danjr1]

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!

[PJ-27]

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.

[Dan-27]

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.

[marto]

If you mess about with the radios you should be able to get them to work. But they were initially calibrated for the HK-T6A which is why they generally work on that ootb.

Steve

[marto]

Just a heads up.

One of the robots in the US Miami competition in a few weeks ago competed with single TZ85as on wheel chair motors in the heavy weight division. So it has now been done.

Steve

[razerdave]

Was that The Big Cheese ?

[leorcc]

Wheelchair motors typically do not draw much current so I guess that would not be a problem.

[daveimi]

I'm using wheel chair motors!