Has anyone who happened to have a well performing, well accelerating battleship class vessel ever measured the static thrust when the ship is stationary? thanks Greg
Yes, We've done it quite a bit over the last two years in the MWC. I've been gathering the data for a rule proposal that is currently being voted on.
Its not posted anywhere public if thats what you mean. Give me a way to contact you and I can send it your way. Why are you interested in seeing it? Doing anything interesting with it or just general knowledge? Also when I send it to you, you have to agree to send me any data you gather on your own ;-) more data is better. Rule proposal is as follows: Rule Proposal 2009.2 Title - Physics Based Reverse Proposal: Replace 2.D. with the Following 2.D. Reverse 1. All model ships must be able to change from forward to reverse motion by radio control. 2. No ship may have the magnitude of its reverse thrust greater than the magnitude of its forward thrust plus 2 ounces. a. Thrust shall be measured statically (ie. Ship in the water attached to a scale) b. Forward Thrust shall be measured at full forward throttle. c. Reverse Thrust shall be measured at full reverse throttle. d. Thrust Testing shall take place immediately after speed testing. Ships That Would Be Affected: ALL Author's Reasoning for Rule Change: We have been working to remove “super reverse” from the rules for a few years now, last year a rule was proposed and passed that does remove super reverse in some cases however it doesn’t do enough to truly get rid of it. There are still plenty of ways to achieve “super reverse”. This rule aims to rid us of “super reverse” completely by using a simple physics based approach. To do this we use our knowledge that F=ma and the fact that we have a top speed limit that is already in use and easy to test/enforce. At this top speed we know our acceleration is 0, because the thrust equals the drag. Rules 2.B.1 and 2.B.4.a-i already take care of controlling drag and any drag addition devices on a boat. This rule takes care of the thrust part of that equation. Since we aren’t trying to control acceleration but only top speed in reverse the mass of the boat is irrelevant. Taking into account general boat hull design practices I think it is relatively safe to say that boats will have less drag in forwards then they do in reverse (they were designed to go forwards almost exclusively in real life). This being the case if the thrust in reverse is equal to or less than the thrust in forward and the drag in reverse is higher than the drag in forward, physics tells us that the top speed of the boat must be lower in reverse than in forwards. The purpose of the extra two ounces of allowed reverse thrust is to account for real world anomalies and imperfections in the drive train (motors, gears, shafts, propellers, etc.) that result in small variations of performance between forward and reverse. This rule would have the effect of removing “super reverse” without leaving loop holes in the rules like the current rule has. I believe this rule to be rather robust in that it is based in the real world physics that affects our toy boats. It is also quick, cheap, and easy to test at the lake.
I will send you a message thru the forum with my email. My interest was propeller design... if I know that thrust (and rpm, which I can spec or estimate) I have a shot in hell of dredging thru the propeller design methodology and trying my hand at designing a better prop for our purposes. thanks greg
I am supprised to hear that "super reverse" is a problem, we have not experienced anything like that in the IRC. Is this currently a problem? Is this caused by uneven setup of the electronic speed controls or the new computer radios? Any additional voltage applied to the motors during reverse could be measured by voltmeter.
Its been a problem, a rule was passed last year that banned some of the systems that people were using to do it, but not everything people were doing. You can do it a bunch of different ways, running outside props in reverse only, varying voltage between fwd and rev, directional props, things like that. ESC and computer radios didn't cause the problem, they just added another way to get the same end result. This year it wasn't a huge issue on the water but I imagine some clever people might find away around the banned systems and figured out other systems to reach the same result, which is why the rule proposal this year was trying to regulate the results and not how you get those results. Its somewhat controversial but thats why we vote on things. Full Disclosure: I wrote that proposal so I might be a tad biased ;-)
Marty, I had the Richelieu and Gloire's reverse dialed down about 50% at the Fall Regional battle (about the same speed as forward speed). When it's up to full speed, the ships stop and back up fast. I used it during the 2008 MWC Nats to help me get out of some rookie mistake situations. At that time, there wasn't any rule to quantify or measure reverse speed. The super reverse rule passed in the MWC during the 2007/2008 vote was an attempt to set a standard and a way to measure it. It involved measuring motor voltage in forward and reverse, then comparing the two readings. The voltages had to be the same. It kinda worked, but seemed to be a royal pain to do the measurement. Directional props could give more thrust in one direction. A motor with advanced timing could be set up to give nearly identical voltages forwards and backwards under no load, but still give more rpm and torque in one direction once placed in the water. I tentatively proposed using a tachometer to measure the prop's forward and reverse RPM. The RPM had to be the same +/- 150 RPM. Given the props are turning the same RPM forward and reverse, then reverse speed should be close enough to forward speed to be tolerable. The RPM check could be done in 30 seconds vs measuring voltage or putting a ship in the water and measuring actual thrust. A ship could still have used directional props to gain a little extra thrust. The extra thrust gained would probably be offset by the extra drag of a ship while moving backwards. Also, directional props mounted backwards would actually hurt turning ability due to less water moving over the rudders (water cone dispersion). I think the proposal was too simple to get much support. Next time we battle, I'll crank the Richelieu back up to full reverse speed and demonstrate outside of a battle.
Thanks Mike and Snipe; I think that Snipe's rule ought to work, I hope we have not given any IRC types any ideas. Marty
Not me, I am interested in the data for propeller design reasons... and information for proper propping of ships.
(Full Disclosure: I wrote that proposal so I might be a tad biased ;-) - Quote- By SnipeHunter I don't think that it's right that you get to count the vote that you authored. P.S. I'm still new to RC combat but i don't think you should count the vote on something you want to pass. You stated "I might be a tad biased".
Shouldn't the voltage drop of the motors be proportional to the work being done by the motors? Therefore, shouldn't the amount of water moved be proportional to the voltage drop of the motors? Full Disclosure: I don't care about super reverse because I drive the same BC props with the same motors with a MAG throttle at all times on the water I can't afford to chance yet another variable in shipboard reliability (those who've battled with/near me know why lol) I know that I could theoretically be more easily gotten by someone using it, but eh, I'm out to shoot peeps and be shot at. Not nearly competitive
Yes. trust our friends I don't know him. He may be cool. but you don't count the vote on your proposal.It's just not right. Hell E.J 2012 and i get to count the vote Woo Hoo i win.
Alright folks, this is not a discussion of rules/regs/who cotes and counts what, this is a thread looking for information on measured thrust. Please keep it on topic.
Advancing the timing on a motor does two things; it raises rpm in one direction and to a certain extent can actually lower the voltage on the direction the motor timing is advanced (the motor is working more efficiently). Of course, I'm talking about a brushed motor like RC car motors with adjustable endbells for changing the timing. All bets are off with brushless motors and some of the latest brushless ESCs on the market today. I agree with Justin Scott though. We have to try to trust our friends. But there is a military saying: Trust but Verify. EDIT: Ooops! Sorry Greg. I remember some thrust testing was done during the 2008 MWC Nats. Maybe someone out there still has the results.
I guess I do not understand how this super-reverse got to be a problem. If a ship has to pass the 100' speed test in forwards, (or reverse), by not exceeding it's allowed speed (at it's maximum speed), then it seems fairly easy, and simple. Mikey
Mike M (too many Mikes!), I agree that one can change the voltages by changing timing, BUT... the thrust delivered will still be proportional to the voltage drop. I guess that would require a new rule that one not change timing after testing or something... *This part not directed at Mike I'm gonna keep building little simple boats. As long as no one bans MAG throttles, regular old props, and poppets, I'll ignore rules talk and leave it to the guys that want to push the limits or stop the pushing thereof.
Hi Froggy, Its not that the super reverse ships were exceeding the speed over a 100' (or equiv) course, it's the fact that they were out accelerating ships that did nothing to improve reverse performance. In a stern to stern duel with haymakers, it becomes a huge advantage. For example , a QE running 4 props in reverse (2 in forward) was able to be halfway down the unarmed side of a Baden before said Baden's single prop (circa 1997 tech & setup) was able to deliver enough impulse to the ship to allow it to move out of the way and even begin to turn out (so much for the Baden's superior maneuverability) The general concensus of the club was that this was a 'bad thing' and that captains should not be forced to add extra systems in order to not become just floating targets for those that did. The current rule banned specific methods. The one that is currently being voted upon modifies it from methods to a specific outcome to avoid clever individuals just finding ways around the ban.
