Sumo Bots C

[paleonaps]

My designs were always over-complicated. Then I built a wedge that always gets in the top 5.

[ichaelm]

My designs were always over-complicated. Then I built a wedge that always gets in the top 5.

Amen! Simpler is better when it comes to engineering and design, in my opinion. Especially in Science Olympiad.

[old]

I can't explain why our bot uses a lot of energy. We have what we believe to be a unique feature, that uses a bunch of power (no it is not a 100 watt diode laser, although that would be way cool, and dangerous, and wouldn't even use a tremendous amount of power). OK, OK we have a high power infrasound generator that drives the competition crazy, but since nobody can hear it, no one will know. Oh, oh, wait, no really we got one of the jammers off an old B-52 and we are going to selectively jam all the frequencies except ours, and our jammer is so good that it will make it seem that the other team is stalling rather than just out of control.

I'll assume that's a joke. Right?

That sounds like it's going to be super-expensive, if you'll need more than 10 battery packs, each rated for extremely high currents. For me, cost is a big issue. If I were you, since we both have very "limited experience" with sumo bots, maybe you should start with a simpler bot to get the hand of things, and then, afterward, work on your super-awesome maximum-performance bot with that special feature. That's what I'm doing now (but without a vision of what to build afterward). Just my opinion.

If mass is such a big issue that you're worried about using batteries that will last longer, have you looked into carbon fiber?

I try to let each thing I do stand on it's own but I will say that I have been very successful at SO at the national level. In order to be highly competitive I have found that it is important to not build too many versions of your design (unless of course you aren't sure about what will work). If we build a regional version and a states version and then a nationals version that will take an awful lot of time, so my philosophy has always been to assume that I will be going to nationals and build a device that I hope will be best at that level.

As to cost: My team try's to reuse as much stuff as we possibly can from previous years. We have a ton of batteries, and motors and R/C gear, and raw materials (like the carbon fiber you mention). We also shop early so that we can buy stuff direct from Hong Kong, which allows us to get some of our high tech stuff at dramatically lower prices than we would pay if we went to the local hobby store. If we used 10 LiPo 900mah 11.1 v batteries, and we needed to buy all of them (none available from previous years) it would cost under $100 from Hong Kong, so that is not a prohibitive cost. The way our team figures it the cost to get to Nationals and stay at a hotel is on the order of $1000+ per student (depending on where exactly we are going) so spending a few hundred dollars on a device that has a good chance at a medal seems reasonable.

We have built similar devices over the years so we have a pretty good idea of what we can actually make work with the resources available (time and money), but you are right that it is very important not to make your project so complex that you end up never finishing. We have seen it happen many times with new team members that they have a plan that is impossibly complex, given the realities of school, sports, band, etc.

As to your question about whether I was joking in my original post: We found that the USAF has rules about using their classified jamming equipment in school science competitions (as does the FCC), and the jammers in question turned out to use astronomical amounts of power (many kilowatts) and weigh well over the 2 KG limit. The laser diode is completely doable but (not expensive, not difficult and doesn't use impossible amounts of power) but it is specifically against the general SO rules on lasers and dangerous devices, and also violates the SumoBot rules on purposefully damaging a competitors Bot. The infra sound Idea doesn't seem to violate any specific rules (it isn't necessarily dangerous) but I don't think our coaches would allow it and I don't think it would actually have the desired effect. So no, we weren't joking! Just kidding.

[Flavorflav]

That's quite a good price, if you can get reasonable shipping. Care to share your source?

[ichaelm]

I can't explain why our bot uses a lot of energy. We have what we believe to be a unique feature, that uses a bunch of power (no it is not a 100 watt diode laser, although that would be way cool, and dangerous, and wouldn't even use a tremendous amount of power). OK, OK we have a high power infrasound generator that drives the competition crazy, but since nobody can hear it, no one will know. Oh, oh, wait, no really we got one of the jammers off an old B-52 and we are going to selectively jam all the frequencies except ours, and our jammer is so good that it will make it seem that the other team is stalling rather than just out of control.

I'll assume that's a joke. Right?

That sounds like it's going to be super-expensive, if you'll need more than 10 battery packs, each rated for extremely high currents. For me, cost is a big issue. If I were you, since we both have very "limited experience" with sumo bots, maybe you should start with a simpler bot to get the hand of things, and then, afterward, work on your super-awesome maximum-performance bot with that special feature. That's what I'm doing now (but without a vision of what to build afterward). Just my opinion.

If mass is such a big issue that you're worried about using batteries that will last longer, have you looked into carbon fiber?

I try to let each thing I do stand on it's own but I will say that I have been very successful at SO at the national level. In order to be highly competitive I have found that it is important to not build too many versions of your design (unless of course you aren't sure about what will work). If we build a regional version and a states version and then a nationals version that will take an awful lot of time, so my philosophy has always been to assume that I will be going to nationals and build a device that I hope will be best at that level.

As to cost: My team try's to reuse as much stuff as we possibly can from previous years. We have a ton of batteries, and motors and R/C gear, and raw materials (like the carbon fiber you mention). We also shop early so that we can buy stuff direct from Hong Kong, which allows us to get some of our high tech stuff at dramatically lower prices than we would pay if we went to the local hobby store. If we used 10 LiPo 900mah 11.1 v batteries, and we needed to buy all of them (none available from previous years) it would cost under $100 from Hong Kong, so that is not a prohibitive cost. The way our team figures it the cost to get to Nationals and stay at a hotel is on the order of $1000+ per student (depending on where exactly we are going) so spending a few hundred dollars on a device that has a good chance at a medal seems reasonable.

We have built similar devices over the years so we have a pretty good idea of what we can actually make work with the resources available (time and money), but you are right that it is very important not to make your project so complex that you end up never finishing. We have seen it happen many times with new team members that they have a plan that is impossibly complex, given the realities of school, sports, band, etc.

As to your question about whether I was joking in my original post: We found that the USAF has rules about using their classified jamming equipment in school science competitions (as does the FCC), and the jammers in question turned out to use astronomical amounts of power (many kilowatts) and weigh well over the 2 KG limit. The laser diode is completely doable but (not expensive, not difficult and doesn't use impossible amounts of power) but it is specifically against the general SO rules on lasers and dangerous devices, and also violates the SumoBot rules on purposefully damaging a competitors Bot. The infra sound Idea doesn't seem to violate any specific rules (it isn't necessarily dangerous) but I don't think our coaches would allow it and I don't think it would actually have the desired effect. So no, we weren't joking! Just kidding.

Cool! You definitely know what you're doing better than I do. Good luck!

By the way, can I ask what team you're from?

[Flavorflav]

Good question. Troy or Mira Loma?

[old]

That's quite a good price, if you can get reasonable shipping. Care to share your source?

We look on ebay in the "toys and Hobbies" section under Radio control parts, engines (I am not on Ebay right now so this isn't exact) and then search LiPo or battery if you are looking at other types. You will get thousands of listings, and you will need to spend some time sorting through it all. If you just type in LiPo or battery at the Ebay home screen you will get a gazzillion listings for batteries for phones, batteries for watches, batteries for B-52 jamming transmitters (just kidding!), etc. Don't expect to just do a search and find the best price on exactly what you want at the top of the list, it will take some time looking through listings. Many sellers from Hong Kong list very low prices but very high shipping (and some times they list free shipping, go figure?) so always total it up to get the real price. Even with seemingly high shipping the prices are still often very good. Sometimes we buy items listed in currencies other than US dollars, but Ebay does the conversion for you (sometimes anyway). We have purchased stuff from many of the sellers in Hong Kong but take some care in checking their feedback and number of transactions. Personally we have never been screwed on anything that we got from overseas (mostly Hong Kong, but also Australia and other places), but it can take a long time to get it (often as much as 3-4 weeks) so don't wait a week before regionals to start looking. Even in the very rare instances where we got broken stuff the sellers have always replaced it, although as I said it can take some time. These big overseas sellers really seem to care about their ratings, they don't sell on Ebay for fun, so if the rating is 99% or better and there are thousands of feedback, you are probably ok. You will get a refund from PayPal if the item doesn't show up or it isn't what was described, or as I discovered when I sold something last year, they will refund the buyers money under virtually any circumstances as long as they can show they sent it back.

[gh]

Folks, a great online shop I and some of my robot building friends use is Hobby City (http://www.hobbycity.com/), which is a Hong Kong-based operation with warehouses in Germany and the US. They have dirt cheap *everything* compared to US hobby sources, especially Li-poly batteries and brushless DC motors, and shipping is pretty reasonable.

If you don't know what you can obtain with your budget, their selection is a good one to browse through.

P.S. I'm just a customer; I'm not affiliated with them.

[sj]

I was wondering what kind of speed controllers i would need if i was using 2 12v gear-motors with a nominal current of 1.5A and a stall current of 148A each. What kind of specs should they have? Right now we are trying 2 12A continuous 45A peak Controllers but that is probably not nearly good enough. any information would be much appreciated

[ichaelm]

I was wondering what kind of speed controllers i would need if i was using 2 12v gear-motors with a nominal current of 1.5A and a stall current of 148A each. What kind of specs should they have? Right now we are trying 2 12A continuous 45A peak Controllers but that is probably not nearly good enough. any information would be much appreciated

My god...

This all fits in 1.8 kilograms? Including batteries capable of supplying 300 amps? Really?