The Drivetrain: Motors, Mounts, Sprockets and Chains
First, we will construct the drivetrain. There are two modules that are part of the drivetrain, the motor assembly and the wheel assembly, that we will put together before mounting them onto the HDPE sheet. You may assemble these two modules in any order since we won’t be connecting them up until the end.
We first have to attach the 16 tooth sprocket to the universal hub using three 4-40 3/8th inch bolts. We recommend that you fasten the sprocket to the universal hub on the shaft to make aligning the hole easier. Once you align the holes for the universal hub and sprocket, we recommend you first hand tighten each of the three bolts before screwing them in place.
You will need to attach sprockets to universal hubs for both the wheel assemblies as well as the motor mount assembly.
Motor Assembly: Attaching the motor to its mount and attaching a sprocket.
The motor mount is what fastens the motor to the HDPE sheet and connects the motor with the sprocket that drives the wheel. In order to assemble this part of the drive train, you will need the following components.
List of Components
Pololu Gear Motor
M3 - .5 x 6mm Bolts
10-32 Set Screw
16 Tooth Sprocket
4-40 Bolts, 3/8th Long
To assemble the motor mount, first take the motor and look at the face with the shaft sticking out. You should see six holes that will align with the six holes in the motor mount. This is where you will be screwing in each of the six bolts.
We recommend that you fasten the bolts in a star pattern rather than a circular pattern, because this makes it easier to keep the holes aligned as you fasten each bolt.
We also recommend that you do not completely tighten the bolts the first time you fasten them. Fastening the bolts is much easier if you screw all the bolts in halfway the first time, and then tighten them completely after you have made sure all the bolts are aligned.
Now we need to attach the sprocket to the motor shaft. To do this, we first have to attach the 16 tooth sprocket to the universal hub using three 4-40 3/8th inch bolts. We recommend that you fasten the sprocket to the universal hub on the shaft to make aligning the hole easier. Once you align the holes for the universal hub and sprocket, we recommend you first hand tighten each of the three bolts before screwing them in place.
Once you fasten the sprocket and universal hub, you should be able to slide it onto the shaft. In order to prevent the sprocket from sliding off the motor shaft, you will have to add a 10-32 set screw to the universal hub and tighten it, as shown in the Motor Assembly video at the right of the page.
Once you tighten the set screw, the sprocket should not slide around on the motor shaft.
Remember that you will have to repeat this process in order to get the second motor mount assembled (since your robot will need two).
If you did everything right the motor mount should look like the following.
What it should look like
The Back Wheels
The back wheel assembly is slightly more complicated than the motor mounts. This is because it is part of the drive train and will be connected with the motor mounts you just assembled with a chain. Once again, it is recommended that you assemble these wheels separately before fastening them onto the HDPE sheet.
Like the motor mount assembly, you will have to build two of these to complete your robot. Below are the components that you will need to complete one of the back wheel assemblies. All of these components can be found in your base kit.
List of Components
Note:Each of the quantities below is to make one set, you need to make two sets total.
See the video describing wheel assembly to the right of the screen. There is a specific order in which the components are secured onto the shaft.
Wheel Assembly: Putting together the wheel, sprockets, axle, and bearing block.
First, take the wheel and slide the shaft through the hole in the center. Locate the set screw (a small inset screw on the outside of the aluminum hub near the center of the wheel) in the aluminum hub at the center of the wheel, and rotate the flat side of the shaft to face the set screw. Slide the wheel to the end of the shaft, with the metal hub in the center facing towards the rest of the shaft.
Then, using your Allen wrench set, tighten the set screw until it is firmly against the flat side of the shaft, and the wheel is locked to the shaft.
Now take the sprocket/universal hub and slide it onto the shaft, bringing it to rest next to the wheel. Rotate the sprocket until its set screw is facing the flat side of the shaft, and tighten the same way you did with the wheel's set screw.
Next, take one of the two nylon washers and put it on the shaft. This will make it easier for the wheel to spin.
You can now take the bearing block and slide it onto the axle block. Then add the other nylon washer.
Finally, take the shaft collar and slide it onto the end of the axle. Slide it close to the nylon washer, but leave enough room between the components that the bearing block can rotate on the shaft. Rotate the set screw until it is facing the flat side of the shaft, and tighten it. Once it is tight, check again that the bearing block can rotate freely. If it cannot, loosen the set screw and move the shaft collar very slightly away from the bearing block, and re-tighten. This should result in a completed bearing block.
Steps 3 and 4
Steps 5 and 6
If you did everything right the motor mount should look like the following
Remember that you will have to repeat this process in order to get the second back wheel assembled (because your robot will need two of them)!