Biomimetics and Dextrous Manipulation Lab

FinalProjectMaterials

Useful Materials and Supplies for Final Project

Also see: FinalProjectConstructionTips

5 March2015 - added Grainger and Olander as quasi-local sources for belts, fasteners, etc.

1.  Hardware and Fasteners

1.1  Screw Posts and Tee nuts

Screw posts (also called "binding screws") are handy for pin joints. You can get them at some hardware stores but they are cheap if you get together with another team and buy a box of 100+. The aluminum ones are stronger and easier to screw together but you may need a drop of superglue to keep them from unscrewing themselves. The plastic ones can be cut to length and don't tend to unscrew but require two large-blade screwdrivers to assemble.

Plastic shoulder screws are an alternative to screw posts. They are more expensive, but stronger and easier to tighten. There are various sources including McMaster Carr.


Shoulder screws are another
option for pin joints

Manufacturing tips:

  • To reduce wobbles, you can glue the female side of the screw post to one link. Only one of the two links need to rotate with respect to the screw post. Use small plastic washers to minimize gaps and friction. It also helps to cut and file plastic ones exactly to length.
  • You can laminate two thin pieces of laser cut material to make a fake counterbore: make a hole in one piece bit enough for the head of the screw. Make the hole in the 2nd layer just big enough for the shaft.

4mm mild steel tubing

Tee Nuts are similar in function to screw posts. They are useful for attaching to a piece of wood (may want to press them into a hole and fix with epoxy for good measure) and they provide a female screw thread to which something else can be attached. Example: Under Fastening and Sealing in McMaster Carr look for "Tee Nuts" or enter "Tee Nut" in their search window.

1.2  Axles and bushings


Teflon tubing for cheap bushings

You will probably need some shafts that transmit torque. Some options:

  • Aluminum rods -- Allthough it's not the usual practice for machinery, we like aluminum rods (perhaps 1/4inch diameter) because they are plenty strong and much easier to cut, drill small holes into and file (e.g. to make a D shape on the end) compared to steel shafting, which is often hardened.
  • For special cases (e.g slipping over the end of Tamiya gearbox 4mm shaft), you could use a mild steel tubing with 4mm inside diameter. Mild steel is easy enough to cut and drill a tiny hole for a pin that goes through the gearbox shaft. Stick something inside the tube to prevent crushing if you use a set screw. This is one case where aluminum may not be strong enough.
  • Bushings can reduce friction or wear on the holes for any shafts with large loads. You can buy these (but they can get expensive if you have a lot). The cheap alternative is to cut slices from a low-friction plastic tube.
  • Plastic washers are very useful to reduce rubbing and "play" or looseness. Like screw posts, they are much cheaper if you buy a box of 100+/
  • Shaft Collars can be made into hubs for links or gears. They have a set screw to clamp onto a shaft and have enough area on the side that they can often be glued to a small gear (including a Lego gear) or link or sprocket if you roughen a bit with sandpaper.

Shaft collar with set screw

Other options:


2.  Motors and gears

  • Various places sell the ubiquitous Tamiya motor kits -- these are cheap and fairly durable. See the picture below for a model that is often used because it has a shaft that sticks out both sides and lets you rearrange the gears for a variety of speed ratios.

Note that while the kits don't say much about the motor, you can sometimes read that they use "the Mabuchi 260 RA motor". If you Google the motor type you can often find a data sheet somewhere. The data sheet will often be for a couple similar motors rated for different voltages. Note also that most of these motors can often be run at up to double their nominal voltage for more power (and shorter life).


Sprockets (Jameco) for plastic chain. You can drill a small hole through hub and inner shaft to pin firmly to a shaft.

Cheap plastic gears (Jameco) -- for these you probably will need to lasercut or otherwise create your own hubs which you can glue & screw to one side for mounting to shafts.

2.1  Gears


Various kinds of positive drive belts
(Stock Drive Products)

In addition to the kit gears from same sources as the motors kits above, you can order gears directly from places like

You can also re-use and modify Lego gears and other components:

In any case, you will want to read the notes about mounting gears to shafts.


Small ball joints from hobby shop

J&M Hobby in San Carlos

3.  Sources

Many of the items in the list above are available from McMaster Carr with fast delivery. Prices are not particularly low, but it's convenient. Local hardware stores Orchard Supply and Home Depot can be useful for screws, small pulleys, braces, threaded rod, etc. Among these ACE on Alma Street is friendly and the closest (10 minute bike ride). Items like screw posts and plastic washers in bulk are often cheapest if you buy a box of 100 or more online from some vendor that specializes in them.

3.1  Closest hobby shops with motor kits:

  • D&J Hobby San Jose (near intersection 85 and Saratoga) - This is a big hobby store with lots of stuff including Tamiya kits, materials, etc.
  • Sheldons, San Jose - This is another big hobby store with lots of stuff
  • J&M Hobby House, 1660 Laurel St. San Carlos -- small but lots of stuff packed in. Usually has the Tamiya Motor kits.
  • Jameco robot store -- gearhead motors. Local pickup.
  • Hobby Engineering has a will-call pickup in Millbrae. Hobby engineering is in South San Francisco. If you order parts before 2pm from their website, then they will arrive the next day.
  • Apparently Frys in Palo Alto has some Tamiya kits too

3.2  Sprockets, chains, drives, etc.

3.3  Other random stuff


Inexpensive shaft couplings - you will likely need to bore or drill out one side for the larger of two shafts.

4.  Wood, Duron, etc.

4.1  Duron

Duron, also called Masonite or oil-tempered masonite, has been a favorite prototyping material for almost 100 years. It cuts beautifully in the lasercutter but you can also saw it, glue it with wood glue, drill it on a drill press, etc. It helps if you scuff up the surface with sandpaper before gluing to help glue penetration. It is less brittle than acrylic, which is an advantage.

4.2  Aircraft Plywood

Aircraft plywood is much tougher than Duron or Masonite. Again it can be glued, sawed by hand or scroll saw, etc. It is not harder than Masonite, so holes with shafts will enlarge with wear in the same way.

Page last modified on March 07, 2016, at 02:47 PM