SES Rock Rover Prototype Design

Lynxmotion Servo Erector Set
1

This thread describes a prototype of a scale rock-crawler-inspired SES rover (aka Rock Rover).

Here is the SES parts list with rough pricing (sorry I don’t think in part #'s) for the first draft design:

7" channel x2 $22
SES motor mount pair x2 $20
L bracket pair x2 $12
tubing connector hub pair x6 $48
3" aluminum tubing x4 $9
6" aluminum tubing x2 $8
5-sided connector x4 $60
ball link set 2-56 x4 $25
threaded rod 12" 2-56 x4 $24
12mm hub pair x2 $16

Total: $245

To get a rolling chassis, these parts are also required:

GHM/PGM motors x4
RC shocks x4
12mm hex wheels x4

Ok, on to the build:

Note: If you were actually screwing this together, the order of events might have to be different to simplify the build process.

Step 1: Build the Pseudo-Axles

  1. Start with two of the 5-sided connectors. Stack them and bolt them together with the 5th side aligned. For reference, this part is in the place where the differential would be on a real truck. Note: You could use the 4-sided connector to save money, but you lose the face as an extra sensor mount point.
  2. Attach a tubing connector hub on each side of lower 5-sided connector. Keep in mind which end is the bottom.
  3. Attach a 3" tubing piece to each hub. Note: In the final design the tubing lengths may need minor tweaking to set the width.
  4. Attach a tubing connector hub to each 3" hub.
  5. Attach an L-bracket to the connector hub on each end. The L part should extend out from the bottom.
  6. Attach a motor mount to each L-bracket. The side where the motor mounts must be perpendicular to the axle.
  7. Mount the motors and attach the 12mm hubs to the motor shafts.

The first axle is finished. Now duplicate the above keeping in mind that the second axle is flipped 180 degrees.

Step 2: Build the Chassis

  1. Take the two 7" channels and attach two tubing connector hubs to each channel on the same side using the 2nd set of holes from the end. The open end of the U-shape should point toward the bottom of the chassis.
  2. Attach the two 6" tubing pieces in between the mounted connector hubs. Note: In the final design the tubing lengths will probably need tweaking.

The chassis is now complete.

Step 3: Preparing the Links

  1. Use a dremel or hack saw to cut the 2-56 threaded rod into 4 pieces 3-4" long. I’d probably start the design with 3" for the four inner links and 3.5" for the four outer links. Note: The link lengths will be a little tricky to get just right. This is the part where having a 3-D design would save time on trial and error. The four top links should be the same length, and the four bottom links should be the same length, but the top length may differ from the bottom length.
  2. Thread the eight nylon ball sockets onto the threaded rod ends. You will probably want to file any burs off the end of the threads where they were cut before you start screwing them in.

Step 4: Attaching the Inner Links

  1. Take two of the threaded ball studs (and nuts) and mount them into each side of the top 5-sided hub at the center of each axle using an SES hole. Repeat for the front and rear axles.
  2. Take two more of the threaded ball studs and mount them on the inside of each end of the chassis (in the SES hole closest to the end).
  3. Now press four of the rod/socket parts into the ball studs. Yes, this will be somewhat difficult to do. If you need to use plyers to squeeze them in, do not put the plyers directly on the nylon or you will damage them, which causes binding in the linkage and a loss of suspension performance.

Step 5: Attaching the Outer Links

  1. Remove two of the screws from each end of each axle where the L-bracket connects to the tubing hub connector. The two screws that should be removed are the top screw and inner (toward the chassis) screw.
  2. Mount ball studs (four total, two per axle) through the inner screw holes.
  3. Mount ball studs (four total, two per chassis channel) to the outside of the chassis in the lowermost SES hole at the end. Or use longer links and the bottom holes of the next hole set in from the connector hubs (I think I prefer the latter.)
  4. Now press four of the rod/socket parts into the ball studs. Again, be careful not to damage the plastic.

Note: In step 5, I’m removing screws from the axle and replacing them with ball studs and shock mount screws. I’m assuming the ball stud ends are long enough. If that’s not the case, another part would be needed (perhaps the Interconnect Bracket) to mount the lower links and shocks to the axles. In this case the interconnect could be sandwiched between the motor mount and L-bracket with the end pointing inwards, and the shock would mount to the top SES hole and the lower link would mount to the innermost SES hole. This modification will also affect (shorten) the length of the lower links.

Step 6: Attaching the Shocks

  1. Attach the bottom end of each shock to the top SES hole in the axle L-bracket. You will need a screw that fits the ball end built into the shock. Use whatever comes with the respective RC truck kit for the shock.
  2. Attach the top of the shock to the to the outside of the chassis in the outermost SES hole at the end.

Note: Ok, this step can also be tricky. There are lots of different shocks of different lengths and they can be mounted at different angles.

Step 8: Setting it Up

This design gets us in the ballpark of a rock crawler. From here, it would probably have to be set up a bit. Some things to consider:

  1. The links can be moved to different SES holes in the chassis.
  2. The shocks can be changed to different SES holes in the chassis or given “shock towers” (interconnect brackets) to raise them above the level of the chassis or change the mounting angle.
  3. RC cars tend to be light weight compared to robots. For this reason, shocks with extra-stiff springs may be needed depending on payload.
  4. We could always measure a successful RC rock crawler design (I have one) to get link lengths, angles, etc. if we really wanted to tune this bad-boy. But I think a lot of different combinations will work as long as the parts are in-synch with each other.

Step 8: Finishing Touches

  1. Mount the 12mm hex wheels to the hubs.
  2. Cut a chassis plate from plastic or aluminum and bolt to the flat top of the U-channels.
  3. Mount your favorite electronics, etc and have fun!

I hope this all made sense. I typed it out quick and don’t have time to edit it right now. Our resident modeling guru Dale (linuxguy) offered to make a drawing. If you still feel like drawing it, I’d love to see it! I really want to build one of these now.

Edit: Fixed some typos.

2

If I understand this correctly, it will not work. You can not stack two of the AHC-02 five sided hubs together the way this seems to be written. The AHC-02’s have threaded holes. There has to be something between the two AHC-02’s, such as tubing with HUB-08 hubs, or maybe an ASB-06 “L” bracket on each AHC-02 that would attach to another bracket, such as the ASB-18 connector. I just happen to have 2 AHC-02’s. :slight_smile:

I am starting to work on the 3D CAD stuff now, but I think step #1 needs some work.

8-Dale

3

I assumed the screws would be long enough to go through both hubs with enough space left for a nut. I wasn’t necessarily assuming that stock hardware would be sufficient all the way around… it would be easy enough to order some screws and nuts from McMaster if needed.

Thanks,
-Adam

4

I have some of the longer 2-56 screws (PSH-05) so I will see if they will go through both AHC-02’s. There would not be any need for a nut because the AHC-02 has threaded holes.

EDIT: I was able to stack two ACH-02 five sided square hubs together. There is only ONE way it can be done - with the fifth faces facing each other (large holes outward). The PSH-05 screws I have will not go all the way into the other ACH-02 though, and I do not want to force them.

8-Dale

5

I always use nuts and loctite, threads or not, but that’s just me. In general, I don’t think any hardware issues should affect the design though. Any project that stretches the limits of the SES may require custom hardware and/or drilling.

6

This definitely stretches the SES a bit. I don’t think Jim envisioned two AHC-02’s being put together this way. :smiley: I did accomplish it though, so if I can do it anyone should be able to do it. The PHS-05 screws seem to be a bit too long, but they do go through the first AHC-02 into the second one plenty far enough for a good solid connection using four screws, Shorter screws would be better though.

8-Dale

7

Excellent! I knew it would be tricky given the small size and difficulty of screwing inside the small square. I thought it was possible though, and you proved it to be so. 8)

8

I’ve proven at least a small part of your design. :slight_smile: This is really getting interesting now. :smiley: I never would have thought to connect two AHC-02’s in this way.

8-Dale