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  • Author Author: weiwei2
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Is this motor powerful enough to run the chasis? -Automatic Weeding Robot #4

weiwei2

Reality struck. despite its 'formidable' looking track, my chasis cannot move properly on the grass.

The video shows that it struggle to move on my garden grass. The motor driver is a ST L298 based motor driver.

It is dual channel but limited to 2A per channel. As one can see on the video, my power supply is also running into the >2A range

and sometimes overload.

 

One way to solve this is to make use of current capable motor driver. I am right now evaluating the option. i do want to try to change to my maxon motor but

i am also bit unknown if it is more powerful or not. In fact i also have 2 DC motor claimed from power tool. However, the biggest problem of using  those are the lack of planetary gearhead suitable for my chasis. Hence for now i put this option aside.

 

Now, i am thinking whether i can use higher current to drive the chasis. It comes with Donshun's http://www.dongshunmotor.com/zl/clxjs/DS-33RS395.pdf

a motor with label DS-33RS3950126700-74.8k

 

In order to move a DC motor there is a few choice, first is simply use a single relay to turn it on and off. This is the simplest form of dc motor control

and i do have a relay shield on hard. The downside of this is there is no speed control, as the motor simply runs at full speed. I actually have tested the motor by connecting it directly to a 30A capable power supply, and observing its stall current. It should be roughly 2.3A, although i also can see sometimes up to 2.8A.

 

The second choice is to use a half bridge, or construct it with 2 bipolar transistor or 2 MOSFET. MOSFET Is more efficient in that it can offer lesser power dissipation.

 

Lastly, it is H-bridge. H bridge is a circuit capable of switching the voltage polarity applied to a load, in this case the motor. L298 itself is a H-bridge. It is to be noted that one can also use 4 relay to make a H-bridge. Alternatively, a DPDT relay can be used to do it. Well i motor driver that can provide higher current for now. i use to have some 10A dc motor driver shield but unsure where they are hiding right now

 

My next step to determine if under higher current allowed by L298 can i run the chasis on grass. The most directly testing it is to drive the motor directly with power supply. As it seems, the culprit in this case is indeed L298. When using higher current, the chasis can run on the field.

 

image

 

So, the next easiest way is to either use a relay driver to power the chasis, or use a higher current motor driver.

 

 

References

https://www.picotech.com/library/application-note/some-power-pwm-drivers-for-electric-dc-motors

  • in reply to shabaz

    thanks for the info. it is nice to find some resources that i have not previously come across. The TLE94112 seems a decent choice

    image

     

    actually i do have a killer last option, but i think it is overkill for the chasis. i actually have this 2x60A brushed dc motor controller

    https://www.roboteq.com/index.php/roboteq-products-and-services/brushed-dc-motor-controllers/313/mdc2460-274-detail

     

    on the Maxon, i did try to disassemble it further yesterday, but haven't really try in details to see whether it can be fitted to the chasis motor bracket. Sometimes this seeming simple mechanical stuff is really off my capability. so do plan to try the electronic way like up the current first.

  • Hi!

    As DAB and others mentioned, it looks like a torque issue. From the last video, it looks like it can travel quite fast, so it's likely that those motors are not geared down enough, causing it to stall if conditions on the ground are not perfect.

    The motor looks very low-power and poor quality, they look exactly like motors used for the past 20 years in children's underpowered toys, so there is a limit to how much gearing down you can do before its too slow to be of use.

    You mention you have Maxon motors too - they are famous for powerful motors, so if you already have those then it's worth a try if you can find a way to gear them down.

     

    Regarding a driver, it is difficult to build a discrete one, (plenty of bad circuits online):

    image

    but there are off-the-shelf options, like these:

    ROADTEST REVIEW: TLE94112LE infineon motor driver shield.

    (See datasheet page 73 to see how to parallel outputs for more power capability).

     

    or DC Motor Control Shield for Arduino

    (only supports one motor so two boards needed, lots of power but only for motors that can work with 8V or higher, so might not be suitable for the motors you choose to use).

  • On side note, since i am not able to do any physical modification on the bot for next few days, i am doing some 'online research', i do have a few pieces of high current (as in >60A MOSFET), anybody has tried to build DC motor driver out from MOSFET before? any good reference?

    as i have pointed up above i also have 'research' onto 2 MOSFET half bridge driver, but any successful will be of great help image

     

    another that i kinda don't understand is, if i use MOSFET to drive the DC motor, do i need the flyback diode across the DC motor? i do have some 30A rectifier diode, 2 pieces of current sensor (which i think can do over current protection)

  • in reply to dubbie

    I am going for a conference up to next Monday, looks like very limited i can provide this week. Let me update in next thread

  • It does seem to be a problem of getting more torque to the tracks. As DAB has previously indicated, you can get more torque from your existing motors, or as you are thinking, you could get more torque from bigger motors - although bigger motors will probably go faster which might not be what you want. Maybe bigger motors with motor gearing might work.

     

    Dubbie