Reliable High Discharge Lipos

[grant_ploughbot]

Re: Reliable High Discharge Lipos

540 used some dewalt motor's, not the big ones though. Very powerful but as you could see just stupidly fast. Being geared that fast reduced a huge amount of torque so by the time the magnets are on its stalling the motor's quite a lot. To get round those issues you would ideally want motor's more powerful than you need, and gear them to a sensible speed, somewhere in between the fast and low speed of what 540 had would be pretty reasonable. I usually aim for around 800-1000rpm at the wheel maximum on 75mm diameter wheels, but that's just my opinion. Any quicker and you are just stressing the motor's more than needed. If you do it this way you'll have less problems if you decide to put magnets in for extra traction.

The way you drive will massively help as well - to help get around these problems in our smaller kits as theyre running for hours is to have custom software in our speed controller's with acceleration ramping built in so that the current when changing direction is massively reduced.

[PJ-27]

Re: Reliable High Discharge Lipos

Acceleration ramping and non linear control will be a big help in reducing the spikes.

540 upgraded to Speed 900s to help with reliability at this years champs, but they went too. I know Dave also had trouble with stripping gears, snapping drive belts, burning out motors... There's always a weaker link and getting drive that powerful has it's costs.

[grant_ploughbot]

Re: Reliable High Discharge Lipos

Not always. I'm not sure whats causing the problems with the gears keep breaking, maybe too much flex in the gearbox or something. If you make fully enclosed gearboxes with the right ratio's you shouldn't have any problems at all. Dave's gearing still is too fast even with the speed 900's in. He would probably get away without burning up motors if the magnets weren't in.

Ploughbot for example uses astroflight motor's. Much smaller and lighter with plenty of power, but being smaller they're easier to burn out. I use them on 15:1, and will probably make the next set at 18:1 as they're still plenty fast enough. I have fully enclosed 2 stage gearbox with TINY gears in. I'm using MOD 0.5 on the first gear stage and MOD 0.7 on the second. I've never had one strip or break or anything and not burnt a motor out on this set up.

[Eventorizon]

Re: Reliable High Discharge Lipos

What would people reckon to this set up...

6x (3 per side) RS775 12V Motor + Banebots P60 16:1 Gearbox + 2x 98mm Banebots wheels

I have calculated a speed at the output shaft when running on a 14.8V lipo to be ~560RPM and have a top theoretical speed of 10Km/H.

And at peak efficiency I should get... 16.4Kg/cm at the ground, which seems a little low... hmmm maybe I have duffed that last bit of maths...

[grant_ploughbot]

Re: Reliable High Discharge Lipos

That's not a huge amount - I've just ran through your calcs and they look about right.
Those motor's are less than 300w each, fairly high speed so not that powerful really. You'd be better off even saving weight just using speed 900's with a custom gearbox.

[grant_ploughbot]

Re: Reliable High Discharge Lipos

Just as a comparison, on Ploughbot running 24v with good lipo's on the AstroFlight 940 motor I am getting 1000rpm ish at the wheels with some losses, 75mm wheels gives me 14km/h or 9mph. Thats a pretty decent speed.
Torque on the floor at stalling is quite different to your 16kg for 6 motors, more like 116kg at stall with 1 motor per side. The astro's are 750W continous, on 24v thats about 35A draw with the effeciency losses. At stall they're 100A max, which takes the power to around 2000w each, probably more like 1500w with losses.
That torque is enough to just about push my old saxo along

[Eventorizon]

Re: Reliable High Discharge Lipos

would a Speed 900 at 22.2V (6 cell) on a 10:1 ratio work (1 per side, though I did think of using 2 ). David runs 6:1 on satanix with his 120mm wheels but he is only using 2 wheels not 6. The bane bots 124mm would be the wheel of choice as we can easy change the shore value of the tyre

[Ellis]

Re: Reliable High Discharge Lipos

Satanix has masses of power. Once underneath I didn't see it struggle once. Thing is, there isn't much point in having drive that is incredibly powerful, because a drill powered robot (such as ours) doing 10mph will hit just as hard as a 1000w drive monster bot doing 10mph. Only benefit I can see to lots of power is if you can get up to speed in a small distance, i.e., lots and lots of torque. Even if you can accelerate to 20mph in the size of the Robochallenge arena, it'll be stupidly hard to drive. 2 drills and a low enough scoop and you're there, in truth.

I'd focus more on making a machine tough and reliable. Rarely is it power alone that wins robot events. In NST's case, it was flawlessly reliable, and it had a powerful weapon. Winning combination.

My point is, a solid Gimson powered box will be just as competitive (if not more so) as a Formula 1 featherweight.

[Eventorizon]

Re: Reliable High Discharge Lipos

I am not really after speed, my driving is terrible so if I was given a missile like satanix I would struggle. I am kind of after just pure grip and push, like 540 had and then putting plots of armour on to prevent NST from ripping it to bits again. But I am adamant that it will have some kind of active weapon be it a disc or a lifter. (this has veared severely away from the title of the thread!)

[PJ-27]

Re: Reliable High Discharge Lipos

In NST's case, it was flawlessly reliable

Except for that one fault where the weapon motor gets stuck on, yeh it's flawless!

[Ellis]

Re: Reliable High Discharge Lipos

In NST's case, it was flawlessly reliable

Except for that one fault where the weapon motor gets stuck on, yeh it's flawless!

Yeah well, aside from that. And aside from the chain coming off the sprocket and yeah... and.

Well.

Well, my point still stands!

[PJ-27]

Re: Reliable High Discharge Lipos

and it had a powerful weapon

Well you got that part right.....

I forgot about the chain coming off!

[grant_ploughbot]

Re: Reliable High Discharge Lipos

Speed 900's at 10:1 sounds OK, maybe a little fast on those size wheels but will check that later.
With regards to not needing the extra power - drills are good, and they drive fast but they just dont have the grunt that sets a normal pusher apart from things like satanix and 540 that can slam people around really well. Ploughbot has got other robots out the arena by slamming them into the wall. Powerful motor's do make a big difference.

Reliability is the key though - design a solid gearbox for them and the correct ratios and you will be fine.

[craig_colliass]

Re: Reliable High Discharge Lipos

If I were to make a feather ram bot I would think of using 4 or 6 Gimson motors with 75mm wheels running of a battery of about 20v. This should put the speed in the golden 750 -1000 rpm

The body would be steel and as small as possible for the stuff inside, the speed controller would be Wotty100 naturally.

To make it more interesting I may add A suction fan to increase down force and grip with the exhaust out the back to help with pushing power.

But that's me.

[ewan]

Re: Reliable High Discharge Lipos

I'd even go for four 14.4V 550 motors at 22.2V with fan & heat sink cooling on all the motors with 100mm wheels- that'd go like a rocket (in other words 10.8mph with silly-fast acceleration provided softer banebots wheels were used).