A couple weeks ago I posted part 1 of my build of BD-1. If you missed it check it out here (http://madebyap.com/2020/03/10/building-bd-1-part-1-3d-parts-finishing/) so you have some context!
Thanks to Michael Baddeley for creating the amazing 3D files for this as well as the automation instructions. Go support him here and start your own build today!
Today we’re working on putting the legs together.
The Lower Legs
- 6904-24S Bearings (2 per leg): https://amzn.to/3a24dMm
- M3x15 Countersunk Flat Head: https://amzn.to/2wiTaQf
- M3 Hex Nuts: https://amzn.to/3a1qbzg
Insert a M3x15 bolt into the lower leg frame so it sticks out into the inner frame. I had to use a countersink to get the bolt to sit flush with the leg. It’s possible that it was just my print, but it’s good to have something you can countersink the head just in case. Here’s the tool I used: https://www.mcmaster.com/3098a642
In the instructions from Mr. Baddeley it says to glue on the leg skin to the leg frame. I suggest not doing this because you’ll have a challenging time getting the bearings to fit properly.
So now fit the 6904-2RS bearings into place. I had to sand a TON to get these to fit. Just take it slow, and don’t sand too much, you don’t want the bearings loose, you want them nice in tight in the hole.
Once the bearings are seated correctly, you can glue on the lower leg skin to the lower leg frame. I used CA glue but you can use whatever glue works best for the material you printed in
If you haven’t painted yet, I’d suggest sanding down the edges of the leg skin so they run flush with the frame. Then mask out the bearings to keep them safe, and then paint.
If you did paint beforehand like I did, I still sanded down the skin to the frame to get it to be somewhat even, and then just put another coat of paint and clear coat on what I sanded. It came out… okay…
Glue the lower greeble in place.
Fit the full spindle into the lower bearing. This too will require a little bit of sanding to get to fit properly. Again, this should fit very snug, so only a light sanding is required here.
Repeat on the other leg if you haven’t done so already. Otherwise, leave all the other pieces and move on to the Upper Leg.
The Upper Legs
- M4x30 Countersunk Flat Head: https://amzn.to/2Wk9FGB
- M4 Hex Nuts: https://amzn.to/3d9QWTZ
- Servo Cable: https://amzn.to/33ud5Is
Fit the leg pulley to the main leg with a M4x30 hex bolt and a M4 hex nut. The bolt should cove level with the leg pulley – this is a must as the toothed belt won’t fit if it’s not flush.
On my prints, I needed to drill out holes for the servo cable. You’ll see exactly where you need to drill so no guesswork needed. Just go slow and make sure you have a piece of sacrificial wood underneath as you don’t want to damage your workbench!
Glue on the shoulder hub to the back of the leg, I used 2-part epoxy for this. Let it cure for about ten or fifteen minutes before moving on.
Cut a good length of servo cable. I used 36” for each leg (the roll I got was HUGE so I had plenty to spare). Run these up the legs through the appropriate channel, making sure you leave plenty on either side. More out of the bottom of the leg as it has to continue to run through the lower leg and then into the base.
Pro tip: Make sure you label each of the wires. These will eventually be your V+, Ground 1, VCC, Ground 2, SDA and SCL. Labeling these now will make your life so much easier when you get to wiring everything up!
Glue in the greeblies. They are designed to fit nicely in each of their respective spots so be mindful of that (if its too loose or too tight, double-check you have the right greeble for the right hole!
Do NOT glue on the piston arm, booster cover top, center hub upper and center hub at this point. You’ll need to be able to access the screw hole later on when attaching the legs to the body.
Assembling the Legs
Take the upper leg and feed the servo cable through the hole at the top of the lower leg and route it down the channel.
Push the upper leg pulley into the lower leg bearing. You may need to sand a little to get this to fit snuggle. Push them together so they are tight but move freely without catching. Also make sure that your servo cable isn’t getting pinched, servo cable is so flimsy it’s easy to break. Now you have an assembled leg.
Now we run the timing belt. This runs from the lower spindle to the upper pulley and back again. You’ll want to position the leg so it makes a 90-degree angle, and position the spindle so it touches the lower leg. I started putting the cable in at the pulley and then worked my way down both sides into the grooves in the spindle.
You’ll want this night and tight.
Next put the hubcover on using a M4x5 bolt. It will self tap into the plastic, and is used to hold the cable in place.
Put the main cover over the timing belt. This can pop into place. I needed to bore out the holes a little bit to get them to snap. You can also use hot glue to hold this down.
Finally, install the legs into the base – threading the cables through the holes. The legs should move freely when pulling the levers underneath.
Uses a M4x25 (or M3x25) bolt and nut and install them into the rear foot holes.
There you go. Your legs are complete!
Check back soon for part 3, when we start working on the body and head!
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