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jmg

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Posts: 7
Reply with quote  #1 
Has there been any talk or consideration for improving the servos that are given with the kits. We have been doing this competition for 10 years and each year we seem to have to replace servo gears due to failure. At $5 a kit, we could have purchased some very nice metal gear servos that would have lasted much longer.

I understand the additional cost to hubs and how supplying each team with all metal gear servos would be an expensive, but we have upgraded the Cortex, changed chargers, radios, batteries, motors, gears and belts, etc... so isn't it time to look at servos? When trying to buy a Futaba 3003/3004 locally (within an hours drive), I called 4 different shops and they all said they do not even stock the 3003/3004 and only one had gear sets in stock. Several of them do not even sell Futaba equipment anymore. Having worked at a hobby shop for 5 years, I know why they don't stock those servos. They are cheap and for a few dollars more, you get twice the quality. I have brought this up before with the higher ups at BEST, but never got a response.

I would also like to see a change in the Duratrax Powerpole connectors that are used. We did not sell those at our hobby store either due to better options. The main concern on that is that we are using a standard plug and then making a connector with the Powerpole connector. Doesn't that provide additional and unnecessary resistance?

I am not trying to make any one upset with the decisions on equipment, just making observations after years of trying to figure out a better way. Thank you for your time.

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jgraber

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Posts: 156
Reply with quote  #2 
Servos:
If you are stripping servo gears every year, you are doing it wrong.
That said, I'll bring up your comments on Servos at the next Kit meeting.
If you have any specific servo pn or suppliers, please list them here.
I have purchased a few different types from HobbyKing, but not tried to test them yet.

Powerpoles connectors:
If you have a suggestion for a better connector than PowerPole, you should post it here.
PowerPole have a good reputation, and are used by other robotics competitions as well.
 The standard Molex connector is not so bad if you leave it plugged in all the time, as recommended.
As the Cortex age out of the warranty period,  some hubs open the case and solder in a PowerPole pigtail,
to remove the extra connector that is your main concern.  
   Consider approaching your hub as a volunteer, and offering to update all the Cortex with a PowerPole pigtail.

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jmg

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Posts: 7
Reply with quote  #3 
We are breaking the servo gears, or really just chipping a gear tooth, but then the whole system is useless until you replace the gear set. To say we are doing it wrong is an opinion that we would have to discuss in person to see our set up. We could use a servo saver (like the ones used in the steering systems of radio control cars) if it was a kit item to help the problem, but at this time it is not. I have been involved in radio control applications of some type for almost 30 years so I do not know how I am "doing it wrong". Our team has been very successful in BEST competitions having won locally, regionally, and placing in the nationals and worlds when BEST had them. I realize the servos have limitations as they are built, but with increased weights of game pieces such as the broken pipe in this year's game, a stronger servo would have been useful. It would also free up other servos to complete additional tasks.

I think part of the problem is that we get a mix-match of parts that were returned from different schools the previous years. While we try and take care and fix/replace our broken parts, the same cannot be said for all teams in our local hub so when we get batteries that are fried or servos that are broken, it is frustrating.

Servos:

http://hitecrcd.com/products/servos/sport-servos/analog-sport-servos/hs-485hb-deluxe-hd-ball-bearing-servo/product 
This servo sells for around $17 and has 4 times greater strength than the plastic gears in the current servos. The current servos we use sell for about $12.

http://hitecrcd.com/products/servos/sport-servos/analog-sport-servos/hs-645mg-high-torque-metal-gear-servo/product
This one is metal geared and sells for around $30.

Plugs:

http://wsdeans.com/products/plugs/ultra_plug.html
This is a widely used plug - $3.50 per set. A bit high, but very low resistance.

https://traxxas.com/products/parts/accessories/highcurrentconnector
This is also a very popular plug that retails around $3.50 per set as well.

I like both of these because they do not have pieces that can separate from the housing such as the PowerPole plugs. I do agree that the Molex connector is fine for a while as well, but also has a high resistance compared to the other plugs. It is also probably the cheapest. I like the idea of soldering in the pigtail and did not realize that was an option. I may talk to our local hub about doing that as an option.

Please do not take my comments as criticisms toward BEST and those who choose the materials we use. I saw the forum and thought I would post my ideas here. I am very appreciative of the BEST competitions and how they are all volunteer run and the low cost for teams to compete. That is why we continue to make BEST the contest we choose to compete in each year and we actively recruit new schools to join each year. To me it is far superior to buying off the shelf parts and seeing who can outspend who.




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jgraber

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Posts: 156
Reply with quote  #4 
Thanks for your positive attitude.
With your years of experience, it sounds like you would be a good hub core team volunteer for the Returnable Kit maintenance.
My snipe of "doing it wrong" was a cheap shot based on a definition that breaking Rkit parts is wrong.
If you consider robotics as a high performance sport, you stretch the limits of available technology and break things sometimes.
If you consider robotics as high reliability sport, the goals and methods can be very different from high performance.
I've no experience with Aircraft RC, but I would imagine that control surface servo applications have different stresses than robotic grippers.
Brainstorming other ideas to work farther within the limits of safety margin on servo uses:
  Motors make stronger grippers than servos;  
  Make your own servo-saver from the springy piano wire.
  Use a damper to damp out tail-wagging oscillations.
  Keep the mechanism main forces off the servo spine,
     ie always use a linkage on the servo, not servo arm directly as gripper.

  
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jmg

Junior Member
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Posts: 7
Reply with quote  #5 
Thank you for the reply. Our hub is based out of a university and I believe there are some college students that get volunteered for maintenance. We do assist other teams with problems and kit material issues (the ones local to us) when asked.

I appreciate you taking the time with your suggestions. We do implement most of the ideas you mentioned, especially using linkages when servos actuate the grippers. The mechanical advantage from doing that is better as well.

We are still exploring ideas and options for better servo reliability. Hopefully we can find something that is more reliable than our current method.

Again, thank you for taking the time to address my concerns. Have a great rest of the robotics season!
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jumitac

Junior Member
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Posts: 1
Reply with quote  #6 
Hmm... that was really helpful for me too. Thanks
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