very nice software... i don't understand anything to these calculations, for me it's just a hobby, but i like to learn and i've another idea...
- Why to not add an optional field for the weight of the truck?
- You could write some alert message, or recommendations, about what to do to make your motor cooler in the case of thermaling, or what do do in case of under/overgearing... you could preconise some solutions (i.e:"reduce pinion gear teeth number to prevent early warming") ??? I think you don't need more that 10 messages to help everyone to set their car correctly...

I really enjoy your work guy!

Squee: Cool, that makes things a little easier. I actually figured the LMTs to have a higher ideal rpm since they have better bearings and magnet structures.

fagzz: I'll have to think on the idea about using vehicle weight as a factor for speed. I still think there are a lot more variables that affect speed like; tire size (width), bearing drag, drivetrain drag, wind resistance, terrain, drive angle (uphill/downhill), and so on.

The calculator is really not that hard. The actual "work" is only about 10 lines of code. The rest is error trapping, input varification, visual appearance, and other "bells and whistles". The same thing could be done (and has) been done in Excel.

Thanks!

Brian, don't get me wrong, the LMT's can handle more RPM's but its safe to say that it will be better on the motor for the 35 to 40k range as well as its were its gonna run cool AND efficient.

fagzz: I'll have to think on the idea about using vehicle weight as a factor for speed. I still think there are a lot more variables that affect speed like; tire size (width), bearing drag, drivetrain drag, wind resistance, terrain, drive angle (uphill/downhill), and so on.


Wouldn't weight be a factor IN all of the above too?

That it would...

Yeah, I forgot that one... :dft001: It just proves there are so many factors that an approximation is the closest you'll get.

I think instead of factoring in all of those...just factor in weight.

that was kinda my point...LOL

But what will factoring in the weight do for you? It would be almost near impossible to factor in the friction due to weight and air resistance as well.

For me, personally? Not a thing, my speed gauge is basically how much it hurts when i hit my shins on high speed passes! OUCH, yeah, that was about 40 mph!!!!LOL

Ah, well in that case you could factor in weight - momentum is equal to the product of velocity and mass :005:

Unfortunately, the problem seems to be that our trucks go faster than the calculator would suggest (which I still think is related to the actual kv rating of the motor vs the published values). Any adjustments would only cause the top speed result to be slower.

Well you figure if you put a lower gear on a truck the amp draw is less the voltage stays higher for the truck will run faster. Not only that but the motor has less of a load so the kv is little higher as well. It should not be for a exact figure but a rough one. The only true way is to get the motors at test them with a speed device. Every body and truck will have a different drag to it for how high the body sits or low as well as the type.

I'd have to believe that either the battery voltage is staying higher than the input value or the motor constant is a bit higher than spec'd. That's the only thing that can account for higher speed than calculated. The thing is, going faster than the theoretical calculated value just isn't possible unless the user is incorrect in one of their input variables. I'd really like to know all the details of someone going faster than the calculated speed, especially if it's GPS verified.

Well, I know for a fact that mine was at least 50 mph simply because my truck does 40 now and it was WAY faster with the XL3100 on 12 cells. A little speed comparo for ya. My truck right now has a 10XL on 14 cells. Its calculated at around 40 mph. My Revo, stock would run right with it. Almost exact same top speed. With the mods I've done, its around 45 mph and slightly faster than the E-Revo. Now, with the XL3100, it went FLYING by my highly modified nitro Revo (which came 40+ stock). It was doing 50 I know. It was almost impossible to control it in a straight line. Since it only says 39 mph, I know for a fact, it IS possible for it to go faster than the calculatos projected speed.

Well, AFAIK, Squee the one that seems the most inaccurate so far. This was what he was using.

EDIT: Squee posted his response before I got mine in...

Version 1.3, not much new, just added a few warnings; one of which is for the 40krpm motor limit.

Tire balooning is the most difficult factor to calculate that could easily increase your speed beyond the calculated value. This is especially true with small tires, which can get pretty tall!

It is pretty amazing how much just 1/4" will adjust speed. I have a warning set for ballooning values greater than 1/2", but thinking that maybe a percentage of the tire diameter may be a better choice. What do you think?

i run 40 series and there is little ballooning, so for me, that would be better. But others? Not sure.

The HPI Geolanders on my Traxxas Rustler that have been used for speed runs become HUGE. They're normally about 4-4.5" tall, but with ballooning I would guess 6-6.5". Obviously that would alter the actual speed quite a bit! Whenever I do speed calculations, tire ballooning is always something I always account for.

WOW! Sounds like my Jato! They do that with my 3.3....I have an Old Rsty that I would like to start as a BL project....not sure how to do that though. So speed calc w/ballooning would be awesome for you!

Just added specs for Jato tranny and diff...

What is the ratio in the jato trans and diff. No spur gear required.

Well, the transmission has small input gears and larger "idlers" gears which form a ratio. The diff is a little tricky because, as you said, there is no "spur". So, I used the ratio of the tranny output gear and the gear on the diff. I checked it against the gearing chart in the Jato manual and it all works out as long as the Jato diff is used in concert with a Jato tranny. Maybe I'll add a notation to the page to inform users that the Jato parts have to be used together to be accurate.

My question is brian. How many times does the input shaft spin to one turn of the output shaft( aka axle to the tires)?

Oops, I guess I misunderstood your post.

The Jato tranny is a little different. You have the input shaft containing the input gears. Then you have an output shaft that has the first gear, second gear, and the output gear together. Then the diff gear is tied to the output gear.

2.066:1 in single speed conversion. Add the "output gear to diff gear" ratio of 1.9:1, that is 3.925:1. Add the stock 54T spur and 22T clutchbell (2.454:1), that equals 9.632:1 total.

2.286:1 in first gear. Add the "output gear to diff gear" ratio of 1.9:1, that is 4.343:1. Add the stock 54T spur and 22T clutchbell (2.454:1), that equals 10.658:1 total.

1.706:1 in second gear. Add the "output gear to diff gear" ratio of 1.9:1, that is 3.241:1. Add the stock 54T spur and 22T clutchbell (2.454:1), that equals 7.953:1 total.

As you can see, you have to treat the output gear of the tranny as part of the diff even though it's on the same shaft as the first/second tranny gears.

All these values agree with the chart in the Jato manual.

I hope I didn't misunderstand your question again.

I wanted to know the two speed version. 1st gear is 4.343 and 2nd is 3.24 to 1 ration with out the spur gear. That is what I wanted to know. I have to add it to a speed calculator i have. :D

Cheater! ;)

Or, you could have looked at the source code of my calculator, it has the same information. :)

Brian nice concept especially for new people to brushless like me, this is great it helps me understand brushless more now beacuse of sutch a simple file. I think rc-monster mike should put this on the brushless part of the store so people can always see what there speed and rpm comes out to!

Great Work Man! Pritty Cool

Brian: See what happens when you try and do something nice for everone. Remember you can't please everyone (Squee) no matter how hard you try. For a newbie like me it's great for a good starting point. You think Squee would like it cause it answers a lot of gearing questions before they get asked a millon times. It would answer even more question if there was a statement like hot motor =smaller pinion needed.(I think that's the right direction). I'm sure Squee could tell me if he not still mad from the start of my reply. Squee I'm just having fun at your expense not trying to be an a**(donkey).

edit: don't forget runtimes on your chart. Add all of this and then the forum would shut down.

All I was saying is, for some reason, it was 10 mph off or more...Thats the only case I've ever heard of, of it being of so far. I was just trying to figure out why....

I'm glad someone can use it! It started as a simple Excel file just for my use but I figured more people might find a use so I ported it over to HTML/Javascript to be easily viewed on any computer anywhere. For those inclined, I made it easily customizable by opening the file and adding whatever other parameters you need. Of course you'd have to save it to your computer first...

Yeah, I suppose I could put the heat relationships on there, but there is already a sticky Batfish put together and I don't want to simply steal it. If he reads this and says it's ok, then I might.

I don't put runtimes because you'd have to enter the capacity of the batteries (one more thing to enter) and even then it depends on a LOT of other variables (weight, driving style, etc) and would be a VERY rough guess at best. As it is, the speed calculator is used to get a general idea of the top speed. There will be variations because of those same variables. Like you said, it's a starting point.

My next addition will be a little section to calculate the diameter of a gear depending on how many teeth there are and the gear pitch. Maybe not as useful in a general way, but earlier I was trying to figure out how big different gears would be and it would have come in handy. Beats calculating it out the long way each time!

yeah I read that sticky a few days ago. A little bit of searching goes a long way. Instead of calling it speed calculator you should rename it to RC speed estimator. On second thought leave it as it is cause somebody will still complain about something. You can please some of the people all of the time but you cannot please all of the people some of the time. I think that's how it goes. Must have been in the other half of the brain. Keep up the good work.

I just made a few more changes... :)

Another update. Added the Neu motors, added Castle Creations Motors, fixed issues with the gear diameter calculator, added other minor features.

R/C Calculations

Hmm... 1.5" is too much extra ballooning for 4.5" tires? You should see the size of Geolanders when the Rustler is going! As for exceeding the RPM of 40,000, it isn't a problem when doing speed runs (or general running with the MM 4600 :005: )

EDIT: Just realized that the tire ballooning thing isn't working like I expected. I typed in 1.5" of tire ballooning for 4.5" tires, and it's saying the tires are 23in. in circumference. I assume that for the tire ballooning part we add the extra diameter of the tire causing by the excessive RPMs, or is it something else? I get the tire circumference at 6" total diameter to be 18in.

Yeah, that's why they are warnings. Some motors have a 40krpm efficiency range, so that's why that is there. I could add a parameter for each individual motors ideal max range, but I have no idea what that would be. I know for the Wanderers it's generally accepted to be ~40kprm. What about the Castle Creations, Neu, LMT, Lehner?

As far as the balooning goes, the value you enter is the extra radius created by high rpm. The formula I used:It's taking the tire diameter (tireD), adding the balooning value (tireB) multiplied by two because that's how much it affects the diameter, and then multiplies all that by PI to get total circumference (tireC). I did this so the user doesn't have to remember to multiply by two themselves. Can you think of a way to phrase the question so that people know what to put there? As to the max value, I figured 15% of the tire's diameter as a generic value. Should it be increased to say, 20% or something? And again, it's only a warning.

Despite the warnings, the calculator will still figure everything out - it just prompts the user to make sure they didn't accidentally enter an incorrect value. There are a bunch of other potential warnings that people may never see just for that reason (like making sure the pinion and spur tooth counts aren't reversed).

Thanks for the feedback though! That's the only way it will get better. I try to make it as user-friendly as possible, buit I look at things from a programming point of view while other people might not, so it is nice to get others perspective.

When I went to put in the tire ballooning, I put in the increase in diameter. It's easier for me to think of it that way. Maybe you could add that the tire ballooning is done by the increase in the radius, so people don't put in the tire ballooning as the increase in diameter.
As for how much tires can balloon, I would say 50%. The Geolandars I'm running:
http://www2.towerhobbies.com/cgi-bin...&I=LXEXA3&P=ML
can easily balloon to 6" without any sort of tape on the inside, which is a 50% increase in overall diameter.

Do you think you could add another vehicle's gear ratio? The Rustler/Stampede have 2.72.

OK, I'll add a note about using radius instead of a diameter for the balooning and make it warn at 50% (wow, that's a lot!).

What exactly is 2.72 on the Stampede/Rustler? The tranny, the diffs?