Rango - Build diary

[overkill]

Yeah, very interested to see those wheels with tread on; the huge contact patch should mean excellent pushing power.

[Ellis]

Thanks guys. Yes, tyres are on. Did a very very brief test drive in the living room (front is too low to test properly) but in that time the ESCs got very warm. I haven't a clue why. The reduction is now rattly-loose-smooth, I really don't understand it. The 885s have got buckets of power demonstrated by the test, but even the 14awg wire was getting warm after just 40 seconds or so of barely touching the drive.

Don't know what else can be done, I'm amazed that the amp draw must still be so incredibly high. Almost undoubtedly, the tz85s will implode half way through fight 1...

[Max]

Are you sure the battery isn't shorting eg. Across the motor casing? Or is the reduction from the motors too high? Are you running off 6s? Do the motors get at all hot?
It sounds like something must be wrong! Have you tried running with the belts taken off?

[Ellis]

No issue in the wiring for sure, have checked. Running 5s. With the belts off there's no load and it goes fine, but that doesn't really help, it kinda needs the belts :b

Motors barely get warm.

I wonder whether this is the first bot to be running relatively low reduction (5.75:1 on 75mm wheels is more than many) with tz85s. It rolls to a stop rather than stops suddenly like T2 always did. Perhaps the braking function of the tz85s is fighting the forwards momentum of the bot, and because grip is so high with the phat tyres, they're being overridden, and as such are shunting power around constantly with no where to go but back into the ESCs.

Aaron? Any ideas?

edit: to clarify, that is indeed what is happening in terms of visible behaviour. It rolls to a stop whereas our other bot, T2, running 24:1 planetaries, stops dead.

[grant_ploughbot]

In all honesty I think it's your ratios that are way off. What sort do RPM are those 885 motors rated for? On my astro's, which are about. 620rpm per volt I used to run 15:1 with 75mm's as it was fast (9mph on 24v)) with bags of torque. I've lowered the ratio to 16:1 on Killer Joule with the same wheels. If your motors are a similar speed to those then that will be your issue. It's only the Genuine speed 900BB Torque motors with a low enough RPM to run that kind of ratio.

[Mouldy]

I had speed 900's in 540 with 80mm wheels on 7:1 and even without magnets the motors kept blowing...bonx is 9:1 I think and his motors still get warm with 2wd...

[maddox10]

Satanix 1.66 uses Graupner speed 900@5S on a 6-1 gearratio to 130mm wheels.

No blowing motors.

[Revsmin]

Skyfall ran S900s on 7:1 with 120mm wheels on 6S, motors got warm, but never the TZ85s

[Eventorizon]

Have you checked all your drive shafts are straight and that everything is running true? There may something that is causing lots of friction which could be messing things up.

What about a dud TZ85?

[grant_ploughbot]

Those robots are 2wd with so gle stage spurs though so hardly any resistance to turning. At just over 5:1 and 4wd with bevel gears and belt drive I think that's the problem. To reduce the strain it might be worth really narrowing your tyres to reduce the friction when turning and see if that helps at all.

[grant_ploughbot]

Another suggestion that Alan just mentioned (discussing it now over dinner) is to leave the tyres on the front wheels and leave the back slippy. That will give you skid steer like venom/360 etc and majorly reduce the current draw when turning.

[harry hills]

Considering the ESC's ran Tormenta 2 fine I don't think that is the problem.

[Mouldy]

If the escs were fine previously then it's for to be the new drive... Tormenta was only 4 drill motors... Big difference!

[overkill]

Is there much heating when you run the bot with the wheels off the ground? if there is still heating, then the problem will be friction in the bearings, if not, then the reduction is too low. The critical thing is to find the specs on those motors.

[maddox10]

Specs, as far as known. 18V 15 Krpm 18A nominal.