Electronics > Electronics
Wireless PC-controlled robot, a bit confused about a few things...
MarZer:
Well, an update on the motors:
I did some calculations using your RMF equation and learnt something quite pleasing. The current weight of my robot stuff is about 5.1kg. I already have all the heavy components, the only things left to go in are some circuit boards etc, which I dont yet have, and possibly some other stuff later, so I based my calculations on a robot with a weight of 6000g (6kg).
The motors I have (I've since learnt are Mabuchi RS-360RH's) are rated at 47.2 g cm torque and 13700 rpm (~230rps, MUCH more powerful than I thought they were :D), giving them a (metric) RMF of 10856. I figure I want the robot to go at least human walking speed (approx 1ms-1) with an accelleration of about 0.5ms-2. To achieve that each motor would need to have a (metric) RMF of at least 5968. Friction notwithstanding, I guess this gives me a large margin of error, as well as leaving plenty of room for additional stuff, perhaps even another battery...
(If those RMF values look very high to you, that's because I did my calculations using grams and centimetres.)
I've also learnt that the motors have a stall current of 7.7A, so if I went the 2x H-Bridge method, they'd need to be able to deal with at most ~16A. You guys know how I'd be able to facilitate that? Could I take an existing H-Bridge design and merely swap components out for higher-current ones? If so, I have no idea what I'm looking for, so a bump in the right direction would be much appreciated :D
EDIT: Incidentally, ILT (or anybody else for that matter), if you did want to collaborate on this stuff, you can find me on MSN Messenger: marzer_ (at) hotmail (dot) com :)
Admin:
7.7A stall current on a 6V motor!?! :o
Sounds powerful . . .
this is a motor driver that can handle 2 motors at up to 10A each:
http://www.dimensionengineering.com/Sabertooth2X10.htm
There are others out there too, just browse.
For a H-bridge to support higher current, all you need to do is facilitate a higher heat transfer rate. Due to internal efficiencies from resistance, there is thermal waste generated that can literally melt the components. To support higher currents, you need to do things like add bigger heatsinks, cooling fans, etc. Or you can put two H-bridges in parallel, dividing the current each gets by half.
But I highly recommend getting the driver, as it will save you tons of time and frustration, and you can use it for robots in the future . . .
MarZer:
Hmmmn, those motor controllers seem to be exactly what I need, the only issue I can see is that they run on 24v DC, the highest voltage I have is 12v DC. Would this be worth a workaround?
Admin:
Actually, the very first line in the datasheet says:
Input voltage: 6-24V nominal, 30V absolute max.
So 24V is the maximum safe voltage, but it will work just as fine on 6V. It will probably run more efficient at higher voltages, say 12V or above, just by the physics of a mosfet. But 6V will definitely work.
MarZer:
--- Quote from: Admin on October 11, 2006, 07:01:11 AM ---Actually, the very first line in the datasheet says:
Input voltage: 6-24V nominal, 30V absolute max.
So 24V is the maximum safe voltage, but it will work just as fine on 6V. It will probably run more efficient at higher voltages, say 12V or above, just by the physics of a mosfet. But 6V will definitely work.
--- End quote ---
Ah, silly me. Teach me for not reading the specs :)
I reckon I will go with the second battery idea, running the PC and such from the 12v, 7ah battery, and getting a 6v, 12ah battery for the motors, servos etc. I did some rough calculations about the added weight etc, and it would seem that the extra ~2.2kg of another SLA battery will still be well within the capabilities of those motorsl.
I guess that means I need some sort of job during the end of year holidays to pay for all of this now... :(
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