You have a power module. Install it, calibrate it, connect the NiMH battery (foolish to use that 4s lipo) and repeat the test on carpet and review the log for power use.
Thanks Dave I will do that, what do I need ticked in Bitmask options to log the information that we need? Is it CURR? I’m at work now so once I’m home I will get on that👍🏼
On the Advanced Parameters Screen page down to the Log Bitmask parameter and check the Current box. You will have to calibrate the voltage and the current sensor. Voltage is easy, you will need a multimeter which I assume you have. Anyone building RC stuff does. For current the easiest way is to fully charge a battery and drive around for awhile consuming the battery. Then adjust the Amp/volt value based on mah logged vs mah re-charged. It’s a simple ratiometric relationship. Some info here about the power module:
http://ardupilot.org/copter/docs/common-power-module-configuration-in-mission-planner.html
Hey Dave, you asked about the C grading on the battery. Wanted to ask you a question.
On the battery I used last night which is the 14.8v 1300mAh it says the continuous discharge is 75C, is that right?
Also on the lipo I’ve ordered it says continuous discharge is 20C.
So does that mean the smaller 1300mAh I tried last night is more powerful than the one I’ve ordered?
C Rating is multiplied by capacity, so for your small lipo it is 1.3A(h)*75=95A and for the big one it is 20A(h)*20 = 400A continouus current.
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400A😳 I think that might cause a fire ffs. Thank you for explaining. Let’s hope it doesn’t damage the rover🤞🏼
It could have the capacity to supply 1 million amps and it wouldn’t make any difference. Current isn’t pumped out like water from a hose it’s drawn by the load.
Would it make a difference to the force/power supplied to the wheels to turn successfully in 360* or is that more from voltage?
its not that simple, it only flows as fast as the smallest restriction, if you drawing loads of current then the battery C rating will make a difference. If you drawing only a couple of amps as you are on a rover then it will make no difference.
The motors specs are as follows for Amp:
No Load Current at 12vdc: < 113mA
8. Current at Rated Load (620g-cm): < 233mA
By looking at the specs above is there a way of better understanding what the new lipo I’ve ordered will do? Would it make the rover be able to turn 360* throughout the duration of a auto mission and for a good amount of time?
From the specs I see the stall current on those motors is 1.6a. So 6.4a is the most current draw you will have plus some insignificant amount to power everything else. There are diminishing returns with simply going with bigger batteries due to weight. 4 wheel skid steer doesn’t help either because of tire scrub. It’s relatively inefficient. So turning that giant battery on wheels around will take some power.
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Thanks for your explanation. Would you say that the battery isn’t going to do the job? It’s a total waste of money if that’s the case. I would have thought the battery would be more than enough but like you said the weight is another issue. On the Lynxmotion website it says the rover can support 5Lb’s of weight which is 2.26KG & I’m way under that even with the battery which is just over 1KG
So basically they are stating that this rover could potentially handle 2 of these big battery’s🤷🏻♂️ But from all your views which I trust that must be total bs from the Lynxmotion website
you might be capable of carrying 100kg, it doesn’t mean you will be sprinting through a field with it for several hours.
As with everything there is compromise between performance (weight) and battery life.
As you know I’m not looking to move faster than 0.50 m/s so providing the rover can move at that speed whilst being able to turn 360* when navigating to each waypoint & being able to do that for at least 2 hours I’m a happy fella😁
So I’m hoping the new battery will provide me with this
It is an easy calculation. Take the worst case, stall (too much load on the motor , so it can not turn anymore) current on all motors is 6.4A plus a bit for the rest of the equipment. To make it simple, let’s say 10A.
So, 20Ah : 10A = 2h of run time, absolutly worst case.
Since the motors should never be stalled for an extended time and the running current is much lower, the actual running time will be much longer.
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Thank you for your calculation. So drive time won’t be the issue, all I got to worry about is if the battery will have enough power to make the rover turn 360* on grass. I just hope it can
As far as power goes you are limited by the max voltage the motors are rated for or 12V. The ~12.6V you can expect from a fully charged 3S Lipo won’t be a problem. So the best you can achieve with any battery is one that can supply 10a at ~12V. More capacity will not produce more power from the Rover it will only supply that power for a longer period of time*. The more weight the more likely you will hit a stall condition. Let’s hope you never hit a stall condition with that battery weight in the driving conditions you have (grade, turns, surface, etc).
*There is one benefit to a big battery in that voltage sag will be slower at the same current relative to a smaller capacity battery. So between that and weight is one trade-off.
With the big battery I do think the weight might be too much so I’m considering to send it back for a refund once it arrives & get something smaller. Reason for this is because today I’ve been testing with the Tattu 14.8v 1300mAh lipo I have & to be honest it’s been moving really well even on grass.
Right now I have managed to get it moving correctly in Steering Mode but once I move over to Auto Mode the rover wants to spin round constantly. I have recalibrated everything like the compass etc & managed to get very good offsets again after elevating the compass high above the rover.
I did Randy Mackay’s throttle & steering tuning also but with no effect. Seems confused with spinning constantly in auto. Is the setup for a skid steer very different & is there anything else I need to configure via mission planner?
@TCIII @dkemxr @David_Boulanger @count74 @ktrussell @iampete
You did read what the others and me wrote about overvolting brushed motors?
If you keep running the motors with a 4 cell lipo, you are going to buy replacement motors real soon.
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The upside to that is after they have smoked they can be replaced with more robust Planetary gearmotors 
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