Hi everyone, I am a mechanical engineer student and me and my team have been assigned to make a UGV that is able to deliver at least 5 kg of water at a 60 m distance and return.
My problem comes in the motor selection. We decided to run with 4 motors (one on each wheel).
I used the on-line calculator provided but the results I get are a bit strange. My specs are:
]Mass (max value) 20 kg/:m] ]Desired Velocity 0.5 m/s (must not be over: 8 km/h)/:m] ]Desired Acceleration 0.1 m/s/:m] ]Expected Efficiency 65%/:m] ]Incline Angle 20 (max value) degrees/:m] ]Wheel Diameter 0.176 meters/:m] ]# of Powered Wheels 4 wheels/:m] ]supply voltage: 11.1 (planning to use: hobbyking.co.uk/hobbyking/st … oduct=9183 as a battery)/:m] ]operating time: aprox 15 min/:m]the results i get are:
]Angular Velocity:27.142 rev/min/:m] ]Torque: 4.6778 Nm/*:m] ]Total Power: 13.289 W/:m] ]Maximum current:1.1972 [A]/:m] ]Battery Pack 1.1972 [Ah]/:m]
What troubles me is the torque field as a value like that seems impossible with the budged we got.
I would be really great full if someone could provide some recommendation on a motor. We currently picked: ebay.co.uk/itm/12V-DC-100RPM … 4d02b71b70
this one but according to the calculator its not strong enough. Thank you all in advanced.
I have one of those 12 volt motors you linked to right here on my desk. They are very well made but grossly under sized for you needs. You do realize they are 25mm in diameter and have a 4mm diameter output shaft. They are well sized to move a 2Kg vehicle if you have four of them.
One hint: Buy motors that are at least 2X larger then calculations show you need. You should be looking at motors used in electric scooters and NOT a lipo battery from hobby king. Power it with a marine deep cycle lead acid wet cell battery (they are sort of like those used in cars to start the engine.) You are building a 20Kg machine and this will cost you a bit. Those scooter motors are about 100 watts and you can run a chain drive or belt reduction to a wheel and then chain the front and rear wheels to drive both with one motor.
Thanks for the reply,our problem is that we have a limited budget since this s university project and they dont allow us to go over 250 pounds for the whole ugv. Last year they used a motor like : gimsonrobotics.co.uk/GR02-12 … motor.html they used 2 of those to move it and it seemed to worked. The specs of this are almost the same as the one i linked. So yea we wont be able to pick 4 motors casting 30 pounds each cause that will leave us with half of our budget just having motors…
5Kg payload needs a ~5-10Kg robot, meaning your estimate of 20Kg is not that far off.
An incline of 20 degrees is also reasonable, and 65% efficiency is also good.
The two main items where you will need to spend money are the motors and the motor controller.
The larger the motors, the more expensive the motor controller.
You can save a bit of money by looking at scrapyards and used /surplus electronics stores for the motors themselves (and perhaps some of the frame?).
At 20Kg, you likely won’t want the weight of the robot directly pressing against the shaft of the motor(s).
Thanks for the reply thankfully i managed to get my hands into 4 of these babies : gimsonrobotics.co.uk/GR02-12 … motor.html
Therefore i am quite sure that they are more than enough since last year they used 2 of them and it seemed to work fine. Also the way we designed the vehicle the motors wont be really loaded or at least in direct contact of a massive load. Again thanks for the replies been great help
The second motor is dramatically larger than that first one you found on eBay. A couple decimal points where lost some place. Just look at the size. One is 22mm in diameter with a 4mm output shaft the other is 44mm diameter with a 12mm output. That eBay motor is TINY. and I’d be afraid to run 1 amp of current through it. The input terminals are suitable for at most #20 wire. It is a very nice motor but not at all suited to a 20Kg vehicle. OK one more “test” My hands are large enough that I can completely hide this motor from view behind my thumb.
On the other hand the second motor you linked to is a very good one and about the size you need. Notice one motor has torque measured in Newton-Meters and the smaller one in Newton-cm. That is a factor of 100 difference.
Beware is stalling torque. You don’t care to much about this because the motor is not moving when it is producing that amount of torque. You care more about the torque at a normal load. Also be carful to compare “torque at gearbox input” with “torque at gearbox output”. They can be different by large factors.
When doing your budget most of the money will go into the traction system, that is motors, motor controllers and battery. You can make motor controllers from salvaged TV sets or where ever you can find BIG transistors for free. Old CRT TVs are good for this. The robot chassis can double as a heat sink. The controller’s H-Bridge can be made from salvaged parts. The lead/acid battery will be the lowest cost for watt-hour you can get but they are heavy. One thing about lead/acid: They can only without a 50% discharge before being damaged. So the 60AH battery has “only” 30 amp hours of usable energy in it.
Scooter motors are cheap. you can buy a 100W motor for $40. That eBay motor is about 2.4 watts at most but would not last long if run at 2.4W My guess is about 0.6W steady state. As I said I can hide it behind my thumb.
