This topic has 5 replies, 3 voices, and was last updated 9 years, 9 months ago by 
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hello,
i have a project and some questions regarding it.
those are the project’s requirements:The robot will move in outdoor and indoor environment and it will carry load of around 8 kg. The speed is not important. Also, the robot will pass slopes (ramps). one important requirements is that it shouldn’t shake or vibrate. it should be very stable and steady while moving. also it should absorb shocks.
my questions are:
which motor should I select? the one with the encoder or the one without? another question is what is the difference between the RoboteQ 30V and 50V motor controller? which one is more suitable for the mentioned project?
the last question is, in case i can’t order the 24V battery that comes with the kit and used another one that it is sold locally. is there specific properties that i have to consider in buying the separate battery in order that it fits the project and the kit? one more thing is that most probably i won’t be able to find a 24V battery, any advice?thank you
While we wait for SDR to reply, I’ll throw in my 2 cents, and ask a few clarifying questions:
What are your robots dimensions?
What size wheels will it have?
Does it have any high power sensors or equipment (IP cam or similar), that will drain more power from the batteries?
Motor size is determined by weight of the robot + weight of the load, but the wheel size and type also play a huge role. The larger the wheels, the faster your robot. You also lose a lot of power with larger wheels. So, I would recommend a smaller diameter wheel (Or possibly tank treads). You can get a lot of forward power with treads because they can be ran off of a small diameter sprocket. However, you have a lot more friction when you try to turn, so you often need to oversize the motors a bit if you want to turn in sand or high friction terrain.I, personally, would advise that you get a motor and a motor controller that can handle encoders. The extra money is well worth it.
Without encoders, it becomes very difficult to drive in a straight line. The encoders allow you to make some very basic code that adjusts the individual motor speeds to maintain a very precise path.If you are planning to carry 8 kg around for any amount of time, you’ll want a good battery.
There are a lot of things to keep in mind with batteries.
They’ll have an ampere/hour rating that will determine how long they last per charge (Rechargeable AA batteries often have somewhere around 2500mAh (2500 milli-ampere-hours), or 1 hour of operation if there is a constant drain of 2500 milli-amperes).
Battery weight can vary a lot from one type of battery to the next. A battery with a higher mAh rating won’t matter if it is also a lot heavier. That just makes the motors work harder to pull the battery… Compare different technologies to see which may give equal, or better, mAh power for less battery weight.
Some types of batteries can be dangerous if they are ever over charged, or permanently discharge if their power drops too low.
You’ll want to make sure that you know the safety requirements of your chosen battery.
For a smooth ride, I recommend that you look in to scripting a PID controller. That is the same math that is used in Cruise Control in cars. It works well to eliminate the rough starts and stops that usually happen with robots.
You can often smooth out motor vibrations by placing a thin sheet of rubber between the motor mount and the robot chassis.
Absorbing shock from the wheels would require proper suspension (Which most robots lack). I’ve never done very much with suspension systems, so I don’t have any advice on that.Advice about specific products, or differences between products, I’m leaving to SDR. They know their stuff better than I ever could.
Good luck.
The RoboteQ are great motor controllers for speed control. ie the controller will increase the power to the motors to keep your motor speed constant. For this you will need encoders (the encoders tell the motor controller how fast the motors are going and how far they have gone). Keep in mind the motor controller can only supply as much power as the motor controller has or as much power the motor has, (ie if you don’t have enough power to climb the hill, it can’t do anything about that). So make sure you have enough power. We have other topics related to sizing motors, etc. The 30V versus the 60V controller is just the rated voltage of the motor controller, other than that they are the same. if you are only using a 24V battery, a 30V is fine, but keep in mind some LiFePO4 batteries will peak real close to 30V, in which case its better to have the margin and go with a 60V controller.
It does not matter what battery you use as long as the battery is rated for the maximum current draw of the motors.
You can get smoother movement when you utilize encoder feedback so any motor that satisfies your load should work fine. Likewise, as Wyldhunt noted, you’ll be able to achieve more defined movement (move directly straight) which is a required for most projects regarding autonomy.
As for the battery, it will depend on your current and weight requirements. Lead acid batteries can output a significant amount of current and are cheap but they are really heavy. Lithium batteries are significantly lighter but you need to make sure that you pay attention to how much current they can put out. You will need to reference your specific battery’s datasheet.
As for your project, if you’re running a 24V system and your battery solution overcharges significantly I would go with the 50V version. Unless cost is a concern you do not want to be operating too close to a device’s maximum tolerances. If your battery system is 24V and it’ll only overcharge to 26V, then you should be fine with the 30V version.
As for the specific motors, I would look at our lower RPM 32mm motors found here (http://www.superdroidrobots.com/shop/category.aspx/32mm-gear-motors/76/ ) or the mid to lower RPM 42mm motors found here ( http://www.superdroidrobots.com/shop/category.aspx/42mm-gear-motors/77/ ). You “may” be fine with four 32mm motors, but the 42mm motors would be a safer bet.
A couple final notes that occurred to me:
When choosing a motor, I highly recommend choosing one with a planetary gear box. They tend to be more expensive, but they are well worth it. They are quieter. They are more efficient (Use less power). They have less power drop from the gears (More power to your wheels). In short, planetary gear boxes are superior to a standard gear box in nearly every way. If you can afford them, always choose planetary gearboxes for your motors.
(You’ll notice that the motors SDR recommended are planetary.)I mentioned that using a PID controller would be very helpful in a robot that needs to remain as stable as possible.
Here is a (External Website) link to the blog of the person who created the PID library for Arduino. If you’re using Arduino, this could save you a lot of time. If not, it could still demonstrate what is involved in making a PID controller yourself:http://brettbeauregard.com/blog/category/pid/
You’ll probably want to check his older entries first, where he’s explaining the concepts and code for his controller in detail.
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