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This question comes up a lot. What type of wheeled robot should I get? We have three different ways of mounting the wheels/axles. Then there are different motors and different wheels, etc. So tons of choices and way to go depending on your needs. You will see the following table on lots of our category pages and support pages
SDR Wheeled Robot Categories Wheel/Axle
Mount MethodIG32
(32mm Motors)IG42
(42mm Motors)IG52
(52mm Motors)DM (Direct Mount) 10 lbs. – – SB (Single Bearing) 75 lbs. 100 lbs. 125 lbs. DB (Dual Bearing) – 200 lbs. 250 lbs. *This is the maximum weight that the robot can handle. Please note that this weight varies widely upon the robot’s configuration and the surface on which it is driven. See our Support Pages for more information. It is important to understand the note at the bottom of this table. The capacity really depends on how you are going to use the robot. The weight restriction is generally not an issue for the wheels, etc. its more of an issue for turning via skid steer. The weight of the robot, its capacity, speed, etc. depend on how the robot is configured. Our typical 4WD or 6WD wheeled robot platforms are skid steer robots (left and right wheels are slowed down, stopped or reversed to turn). Since it has to skid to steer, friction is the major contributing factor for sizing your components. The more the robot weighs, the harder to turn. The higher the friction coefficient (deep grass, carpet, etc.), the harder it is to turn. The lower RPM motors have lower speed, but more torque for easier turning. The default options listed for our robots are what we recommend as a good starting point.
the dual bearing (heavy duty) ATRs use two ball bearings per axle to support the weight. The axle is then chain driven by the motor to spin the wheel. This is the best method since the motor is not under any load other than rotating the shaft. Of course that may be overkill for light duty applications and not worth the extra expense. Our most popular are our single bearing (standard duty) ATRs where a shaft is directly mounted to the motor, but the outboard end of the axle is supported by a bearing. This takes some of the load off off the motor and works great for standard duty applications. The least expensive method (the method most other robot manufactures use) is direct mounting the wheel to the motor. This works fine for light duty applications, but don’t be fooled – all the weight of the robot is being supported by the motor, and they are typically not designed to handle weight.
From a customer email:
I missed the tutorials here
I noticed you built a custom robot that seems to be direct drive as opposed to using sprockets and chain.
How does that perform comparatively to the chain driven model that I purchased?
chain drive is a lot more heavy duty. the wheels are supported by dual bearings as opposed to direct drive. The direct drive one does well, just can’t load it up like the dual bearing HD ones….
Customer Replied:
OK the reason I asked is because the spec payload for the one I bought was 50lbs (285 rpm I52) but the custom one says 75lbs. With the custom I don’t have to deal with chains and sprockets. Simple is best for my purposes, especially at that payload. Is there a long term difference is durability?
That is a mistake on our part. The IG52 DB Heavy Duty ATR you bought has the same RPM motors (i.e. same torque) as the custom length. Yours has an extra reduction with the chain and sprockets (1.5:1) so it would actually be able to handle a bit more than the custom length. We rate the robots’ payload on how much we can load it up and still be able to turn it. So the payload also depends a lot on the surface you are driving it too. Driving on slick floors it will be able to handle a lot more than on rough concrete for example. The custom length could handle a 75lb payload on a slick floor but probably only 40-50lb on concrete. The IG52 DB Heavy Duty ATR should be able to do 50lb+ on concrete.
As far as durability goes, the tires may wear slightly faster with higher payloads but that’s it. The bearings are rated to hold much more weight than the rated payloads.
Customer Replied:
Got it. Most of my payloads will be on normal ground, dirt and grass. 50 lbs still feasible with the custom?
Since I am using encoders, is there an advantage using chain/sprockets? This will be an autonomous robot that will have fairly precise movement.
When making an autonomous robot, its better to error on the heavy duty side and have plenty of torque. When you drive a robot around with a simple RC, you observe the wheels are spinning or stalled, struggling, etc and you back off on the stick. when going autonomous things get more complicated. The motors try to do exactly what you command and its best to have the capacity to handle it. Encoders will tell you that the motor is turning, but it will not tell you if the wheels are slipping… Does not matter if chain driven or direct drive. the chain drive helps because the motor is under less strain and you get a little extra gear reduction. The autonomous program should be looking at the encoders and determine if the motors are stalled and stop applying power. If you have plenty of power/torque this should be a rare thing. Typically if you run an autonomous robot and a RC robot side by side everything being equal the autonomous motors will be hotter from working harder trying to do everything exactly like its being told via speed control and or position control, so be conservative and make sure you have plenty of power and the wheels, etc are supported properly.
On step 3 in this video, , it shows installing the sprockets.
In the PDF installation guide, it talks about drilling a 1/8″ hole into the motor shaft.
I don’t see that done in the video. Is it still necessary?
If so:
My I52 motor shafts are round with a flat side. Where should the holes be drilled? There are two set screw holes.How about the wheel shaft? Do I still need to drill after it the sprocket finds the sweet spot?
Also, the PDF doesn’t detail the location of where the sprocket should be mounted on the wheel shaft.
Nevermind, it looks like the link above has extra instructions not included in the youtube video portion itself.
Step 3: Mount Sprockets to Motors
The wheels in this robot are chain driven so we will need to mount sprockets to the motor shafts and later to the axles. These are the 14 tooth sprockets with the 12mm bore. Before mounting sprockets, approximate how far out on the shaft the teeth need to be to line up with mating sprocket on the axle. Unscrew set screws and place sprockets on motor shaft. Tighten set screws making sure to tighten the first one to the flat spot on the motor shaft. Use thread lock and make sure set screws are very tight to prevent any backlash.
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