Assembling The Arms

Maslow4 has a few parts that need to be glued so we will start there so that the glue can begin drying. In all of the cases where we use glue, the glue is not structural, it is just meant to hold parts in place that might move due to vibration. Use just a small amount of glue.

Assembling the arms is the most complex and difficult part of the Maslow4 build process so we’re going to jump right in and start there.

Find any of these steps confusing or get stuck? Don’t forget, you aren’t alone! Maslow is a community driven open source project. Ask in the forums and we’ll figure it out together!

First we will gather the four belts, the four arms, and the super glue which we will need for this step. The top and bottom halves of the arms are identical.

Removing the spool from each arm, place a small drop of super glue in the slot where the belt will attach like this.

A couple notes on this section. The super glue is opened by twisting the top. One end of each belt might fit into the spool more easily than the other so it’s worth checking both ends before starting with the glue.

You do not need to use much glue. A very small drop is fine. 

Then press the belt fully into the slot. It should not stick above the top of the slot. 

Repeat this step for all four spools.

Next we will glue the encoder magnets into the rollers. For this step we will need to gather the eight rollers and the four magnets.

We will just need four of them for this step:

Note that each roller has two ends. One end has a shallow recess to hold the magnet. That is the side we want to use.

Again using a drop of glue place a magnet in the end of each of the four rollers. Note that the magnet will be slightly recessed below the top of the roller.

Be careful, the magnets will try to stick to things while the glue is drying.

The magnet is symmetrical so it can be placed in either orientation.

Now set those aside to dry. Be careful not to put them too close together while drying because the magnets will attract and stick together. You have to place them further apart than you might expect. 

Next, we can start working on assembling the rest of the arm. To do that we’re going to need to collect our hardware bags, our thread locker, a DC drive motor, and an encoder board.

The first thing that we are going to need to do there is to insert these two nuts into the end of the arm because they will be covered later when we need them. Don’t forget this step or you will have to backtrack a lot later (a mistake I’ve made many times). Using the allen wrench as a guide can help get them in place.

Next place the encoder board over them. There are two guide pegs which will hold it in just the right place.

Then place the motor over that. The orientation of the motor does not matter.

The bolts which connect the motor to the arm can wiggle themselves loose over time so we’ve included removable thread locker in your kit. Place a small amount of thread locker on four bolts.

You will need to cut the end of the thread locker with scissors or a knife. Note - Do not use the super glue here. The thread locker is a blue liquid, while the super glue is a clear gel.

And then bolt the drive motor into place.

Community Note: There is some play in how these bolts attach the motor and having the motor further forward (to the right in the picture) is better than further back. If you find that the gears are too tight in later steps you can loosen them up by moving the motor forwards.

Next we need to collect our drive gear (which has a D shaped opening in the center) and set screw:

Thread the set screw part way into the drive gear:

Then attach it to the motor shaft. The gear should be almost but not quite touching the plastic or lifted up about the width of an index card or three pieces of paper. Tighten the set screw to lock it in place.

Next collect the idler gear (which has a round opening in the center) and the idler shaft along with our packet of silicone grease.

Insert the idler shaft into the arm next to the drive gear. Feel free to bang it on the table a bit to make sure it’s all the way in.

Then place a small amount of silicone grease on the shaft and inside the gear and then slide the gear into place.

Next we need to press bearings into the arm. Press two bearings into the opening in the front of the arm. You can use one of the rollers that doesn’t have a magnet to help press them into place if needed.

Next set this half of the arm aside and we will work on the other half. First we will need to press three bearings into a new arm half. The middle bearing on this side is a bit snug so some GENTLE taps from a hammer can help press it into place.

Next we will attach the belt guard. Insert three nuts into the holes in the top of the belt guard with the open end of the nuts down.

Then add three bolts to hold it in place.

Next we need to wait for the glue to finish drying on our other parts before we can proceed. Feel free to repeat the steps up to this point for all four arms. If you feel like continuing to work on other parts of the machine while the glue is drying you can start on the Assembling the Sled section.

This next part where everything comes together sort of happens all at once and can be a little tricky. Don’t feel frustrated if it takes a couple of tries to get it right. With practice it can be pretty smooth, but the only way to get the hang of it is to try.

First place the spool with the belt wrapped around it onto the top of the arm so that it engages with the drive gears. The fit will be quite snug.

Note that when we route the belt we want it to pass in front of the drive gears, not behind them.

Next on the other side of the arm thread the end of the belt through the belt guard and insert the two rollers. Note that one roller has a magnet and the other does not. The placement of the magnet is very important. It must line up with the sensor (in green on the right) on the other half of the arm when the two halves come together.

Then press the two halves together. This is much easier said than done and this is the trickiest step of the build process. 


Generally I start from the back of the arm (the side that doesn’t have the belt coming out of it) and work my way forward. 


There are three things which will need to go into place. First the idler shaft needs to align with the hole on the opposite side. Then the drive shaft needs to align with the opening in the bearing on the bottom, then the rollers will need to line up with bearings on the other half. 


I find that by checking each one of these locations in turn and getting them lined up the two halves will come together. It can be helpful to use the allen wrench to jostle the rollers around to make them line up.

Then we join the two halves together with eight bolts.

Two of the bolts at the front already connect to the captive nuts there. If those nuts are out of place, I find the Allen wrench works well to jostle them back into the right position.

The other six go around the center of the spool. The direction of these bolts can go in either direction. Don’t over tighten these, they just need to be tight enough to keep the two halves together.

Finally we need to attach the belt end to the end of our arms. Gather the eight belt end parts:

Then take two of the belt ends and the end of one of the belts extending from our arms:

Fold the belt over and press it into the slot in the belt end so that the end protrudes only slightly. This can be tricky to do because the fit is tight (it needs to be tight to handle the force). I find that starting with the loop in the belt at the open end of the slot and pushing it forward works well. You can use the allen wrench to lever it into place.

Then press on the other half of the belt end. 

And secure it with a bolt and non-lock nut.

Congratulations! You are done with the most difficult and longest part of the assembly process!

Next lets assemble the sled.