Alternatives to Pinion and Spur Gears
 

Hi,

I'm making a CAD for a Logomtion roller gripper and I'm stuck at the power transmission stage.

At the present moment, I have an RS395, a pinion gear and a spur gear driving a 0.5 inch hex shaft. My issue with this is that pinion gears and spur gears are hard to source.

Is there any alternative to this? I've attached a picture of the current design.

I've considered polycord, but the joining kit costs $1200 here and we don't want to spend that much.

Re: Alternatives to Pinion and Spur Gears
 

We have been able to join polycord pretty nicely with a bunson burner (had one lying around) heating up a big steel sprocket to melt the ends. Net cost to us, $0.00.

Also, your roller is probably spinning way too fast. Worth checking and comparing. 971's has something like a 25 to 1, or a 16 to 1 gear reduction, and I wouldn't speed that up more than 2x if at all. Check the surface speed of your roller. It probably shouldn't be much more than the speed of the robot.

Re: Alternatives to Pinion and Spur Gears
 

Friction rollers could be a poor man's geartrain (the slippage could even be an asset). There's always chain too (maybe plastic chain, because it's a bit easier to deal with than metal in small sizes). Vex parts, if available, offer a lot of options as well.

If you want to weld polycord, though, you can do it with an open flame, or a hot plate and some ingenuity. The kit is fine, but not necessary for most small jobs.

See here for more ideas.

Re: Alternatives to Pinion and Spur Gears
 

The urethane belt joining kit is not worth the cost. You can make your own clamping and joining jig for little to no cost, and use something like a "Hot Knife for Her" from your local Michael's crafts store to melt the ends.

You can also use timing belts.

On the gear reduction, you probably do want something up around 16:1 or slightly more.

Re: Alternatives to Pinion and Spur Gears
 

You should definitely fit a small gearbox to the motor, and I think you can get away with friction wheels - it probably will only slip when the tubes are fully acquired, which is ideal.

Re: Alternatives to Pinion and Spur Gears
 

You can get hollow urethane belting from McMaster-Carr that uses metal barbs to join the ends if you don't want to weld your own polycord. We have used it a few times over the past couple seasons. Just be sure you cut the ends of the belts as straight as possible and the barb won't come out.

Re: Alternatives to Pinion and Spur Gears
 

We've used a lot of polycord over the years and have never had the joining kit. We join the ends using a standard lighter that you can buy at a gas station for $1, then just let the person with the steadiest hands hold it together until it hardens. We've never had a problem - polycord is ver flexible and doesn't need to be perfect.

One of the biggest reasons we would use polycord in your design is for weight distribution. Using the polycord can allow you to move the motor further from the tip of the arm.

Re: Alternatives to Pinion and Spur Gears
 

We've always used an old soldering iron for our polycord.....we ground the sides more or less flat and used it as a knife between the edges....then just join by hand.

Re: Alternatives to Pinion and Spur Gears
 

Take a look here. This supplier is the place to go for transmission products.

http://www.sdp-si.com/eStore/CoverPg...Components.htm


Roy

Re: Alternatives to Pinion and Spur Gears
 

Here is a shot of our prototype from this year that was made from less than $200 total materials including transmissions, polycord belting (fused with a grill lighter), spockets, #25 chain, and Al hex, plate, and round stock.

http://www.chiefdelphi.com/media/photos/37060

We made 5 iterations out of Rought $200 worth of raw materials including the final one shown here:

http://www.chiefdelphi.com/media/photos/37063

The powertrain is banbots RS-545s through banebots planetery transmissions, then a 1:1 driving the rear rollers and the polybelting driving the front rollers.

This is a simple design that looks fancy only because of the machining. We had a wood prototype week 1 of build to test out the dimensions for claw before cutting metal.

Re: Alternatives to Pinion and Spur Gears
 

#25 chain and sprocket... use aluminum sprockets from AndyMark
Pretty light... easy to service... just watch the RPM's

Re: Alternatives to Pinion and Spur Gears
 

I'm not sure if some of the people in here realized you were from Australia and shipping from the US is quite difficult, so some suppliers like AM and McMaster might be out of the question for you.

I was able to find one Australian Company that might be a good supplier for things like chains and belts. http://www.smallparts.com.au/ Seems like they carry a lot of the things suggested in this thread.

Re: Alternatives to Pinion and Spur Gears
 

Polycord is excellent for many purposes. Our grabber from last year used two loops with one being in a figure eight to reverse the direction. It has a significant advantage of slipping rather than putting your motors into stall.

I'm a little worried about the people using open flame to join the ends. I was told by our supplier that the fumes from burning urethane are BAD.

Here's a simple tip: use a hot air gun. Shield all but the ends from the hot air and be patient. When the ends are looking nice and soft mash them together in the corner of an L-angle (to keep the cord aligned) while wearing some gloves (so you don't get burned).

Re: Alternatives to Pinion and Spur Gears
 

We have a slight weight issue too because our elbow is being run off a CIM and 27:1 Banebots P80 so we can't output as much torque as we'd like.

We have surgical tubing to counter-act the torque, but we're not sure how well it would work for heavier loads.

Peter, how much does the Bobcat gripper weigh? I'm trying to minimise weight in the design.

Re: Alternatives to Pinion and Spur Gears
 

It weighs about 10 lbs including motors and transmissions. We planned for the weight from the begining because we knew the claw needed to berobust enough to take direct hits fromother robots. We could have shaved weight out by making it from 1/8" instead of 3/16 but we had prior experience saying that you can never have enough robustness for a claw.