Speed Calculator

[MetalMan]

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.

[neweuser]

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!

[BrianG]

Just added specs for Jato tranny and diff...

[coolhandcountry]

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

[BrianG]

Originally Posted by coolhandcountry

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.

[coolhandcountry]

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

[BrianG]

Originally Posted by coolhandcountry

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.

[coolhandcountry]

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

[BrianG]

Originally Posted by coolhandcountry

...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. :)

[Mike.L]

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

[go4gold]

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.

[squeeforever]

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....

[BrianG]

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!

[go4gold]

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.

[BrianG]

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