Gear Ratios

[losikid]

I am trying to come up with a plan for a motor on wheel crawler but i'm no genius when it comes to gear ratios, so does any one know what a good gear ratio be for a Motor On Wheel super, i'm wanting to do a spur mounted to a shaft that has a wheel hex on it and a pinion on a motor to keep it as simple as possible and as low budget as possible, so any ideas for gear ratios would be helpfull

 

[oldhippie]

I think the spur might end up bigger than the wheel/tire. To get even 50 to 1 you need a 500 tooth spur and 10t pinion.:?

 

[house_Fly]

not sure where your getting your numbers.

If I am wrong I am sorry for posting that, but from what I understand this applies to other vehicles as well. Worked on my ruslter for speed.

 

[oldhippie]

It is a math thing. :? The above chart is for a overall gearing of a rig with reduction in the trans and axles plus the spur/pinion. So the spur/pinion ratio times the trans ratio times the axle ratio = the overall ratio. With just a spur and pinion providing the overall reduction 500 divided by 10 = 50. About the same overall ratio as 87/14 on the chart (stock ax10). 8)

 

[hitman46mod]

Old hippie is right. The chart you have shows Final drive numbers for a trans with a reduction of around 7.69:1. ie 90/10 X 7.69 = 69.21

And as for a motor on wheel rig. While it is a fun idea, do you have any idea of how heavy a rig with 4 motors, and transmissions would be?

 

[Stormin2u]

The chart shows 15 and 16 pin 87 spur as the same gear ratio.

 

[Terranaut]

losikid, I'm interested to see how this develops.

I would suggest working out your desired wheelspeed in RPM, and find the no load speed of the motor you choose to use, then calculate the gear ratio from that. Next step is to consider how to achieve the rquired ratio.

Wheel speed is easy enough to calculate.
1/ Start with miles per hour (MPH) that you think will work, divided by 60 equals miles per minute, multiplied by 5,280 equals feet per minute. For example 3MPH = 264 fpm.

2/ Put a mark on a tire and roll it along the floor for exactly one revolution, measure the distance it travelled in feet. (eg: 1 foot 6 inches = 1.5 feet.) For example a 7" diameter tire travels about 1.8 feet per revolution.

3/ Divide the result of 1/ by the result of 2/ should give wheel speed in RPM. For example 264 / 1.8 = 146 RPM.

4/ A little search on this forum should yeald a no-load RPM for the motor you have in mind. A 55T 540 can motor on 2 cell LiPo makes roughly 7,000 to 8,000 RPM, but don't quote me on that!

5/ Divide 4/ (motor RPM) by 3/ (wheel RPM) will give the gear ratio you require. In my example 8,000 / 146 = 54.8, so that means you want 54.8 : 1 gear ratio.

These are very simple calculations you can do with the calculator function in a mobile phone, or just pen and paper. I think it is likely that you will need more than one stage of gear reduction to achieve the right ratio, simply because, with a 10 tooth pinion, you would need a 548 tooth spur (in my example above) and that's a huge spur gear! It could easily be done with two stages though.

Hope this helps.

Cheers.

 

[ToyTundra]

Gearmotors would be the best way.

 

[Sharkey]

a gear reduction box such as the hpi http://www.hpiracing.com/products/en/87634/ at around 7.56:1 or rc4wd http://www.rc4wdstore.com/2/product_info.php?cPath=27&products_id=214 at 2:1, 3:1 or 4:1. couple that with your spur and pinion to get a crawler friendly ratio.

 

[losikid]

well is the gear ratio that the hpi puts out becasue it says 23:1 to 174:1 so what is the actual reduction of that gear reduction box compared to a the rc4wd which is a 4:1 also does anyone know which one is beefer, i like the idea of a bolt on gear reduction to the motor, now if i was to use one of these what would be a good spur pinion combo for probably a integy 45t or 55t

 

[Sharkey]

the hpi box converts the wheely king's overall gear ratio from 23:1 to 174:1. 174/23 gives 7.56, so that would be the ratio reduction of the hpi box.

 

[losikid]

well i'm thinking the rc4wd one since it fits nice and uniformed with the motor, so what would my spur and pinion size have to be to get a good gear ratio

 

[2500hdon37s]

well i'm thinking the rc4wd one since it fits nice and uniformed with the motor, so what would my spur and pinion size have to be to get a good gear ratio

I'm not sure on the pinion size (I'd say small like 12-10) but your spur would still have to like a 90t with the rc4wd 4:1 unit
how would you ever mount all that on the wheel hub area even on a super and still have steering and being able to have a sturdy enough area to keep all your gear's meshes from getting out of wack or will it be more of an MIA (motor in axle) where you run a shaft out to the hub and knuckle with the motors in the center of the axle the the gear reductions as you get closer to the hubs?

 

[losikid]

I'm not sure on the pinion size (I'd say small like 12-10) but your spur would still have to like a 90t with the rc4wd 4:1 unit
how would you ever mount all that on the wheel hub area even on a super and still have steering and being able to have a sturdy enough area to keep all your gear's meshes from getting out of wack or will it be more of an MIA (motor in axle) where you run a shaft out to the hub and knuckle with the motors in the center of the axle the the gear reductions as you get closer to the hubs?

Well i had an idea to get it all mounted but i don't think my plan will work with a spur that big, so what i'm wondering is if the rc4wd can mount multiple gear reduction units in a row so 3 of them would give me a 66:1 gear ratio which seems like is the general area of gear ratios I've been hearing, so if i can do this i can mount the output shaft right onto the axle stub

 

[Terranaut]

The RC4WD units may not fit back to back, but the idea takes you straight back to gearmotors, which do exactly that.

Gearmotors would be the best way.

Cheers.

 

[losikid]

The RC4WD units may not fit back to back, but the idea takes you straight back to gearmotors, which do exactly that.



Cheers.

where do i get a gear motor that is 540 size or smaller

 

[Terranaut]

Gearmotors are commonly used in industry, there is such a wide variety that I would be reluctant to try to second guess you and suggest a particular unit. They are available in a wide range of motor sizes and types, with or without vatious sensors built in, and with many gear ratios and other options.

There are so many search options too, but I'll offer one that I use, globalspec.com . Sorry, but you really have to do this yourself, or pay me a consultants fee. :mrgreen: Here's about 3,000 gearmotors to get ya started, you really need to register (free and easy) and refine the search. http://motion-controls.globalspec.com/SpecSearch/Suppliers?QID=16454766&Comp=17&fc=1 I hope you find something you like, good luck.

Cheers.

 

[losikid]

well i have a few quotes coming but they all need to be custom gearmotors and i doubt the quality of the motor and gears will be great, considering that the prices will be way over priced (i'm assuming). But we'll see what the price is

 

[ToyTundra]

well i have a few quotes coming but they all need to be custom gearmotors and i doubt the quality of the motor and gears will be great, considering that the prices will be way over priced (i'm assuming). But we'll see what the price is

www.robotmarketplace.com has a small selection of gearmotors. The beetle motors are pretty tough and small. I use a 24mm outrunner on the 104:1 box.

 

[losikid]

www.robotmarketplace.com has a small selection of gearmotors. The beetle motors are pretty tough and small. I use a 24mm outrunner on the 104:1 box.

Well i went through there and i think there was only two for a 540 size motor
http://www.robotmarketplace.com/products/RP-MAGNUM775.html
and
http://www.robotmarketplace.com/products/0-BHG62.html

I'm thinking about a the second one and changing out the motor either with a a integy 55t or a titan 21t (the motor on it is the same dimension as the titan)