### Author Topic: Calculating Sprocket For Treads  (Read 1722 times)

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#### Mastermime

• Supreme Robot
• Posts: 316
##### Calculating Sprocket For Treads
« on: March 18, 2012, 08:19:12 PM »
Hey guys,

I am a bit confused.  Will this formula still apply for finding the sprocket I need when I am using treads.  Velocity= Circumference*RPM.  Then solve for RPM.  Or does this only apply when using wheels?

When I try and do this, I am getting a low number for the final RPM so I don't think I have the conversions, right?

Here is the info

Circumference of treads:69 in
Desired speed: 10mph or 10560 inches per minute
Drive Sprocket: 11 tooth

Thanks

• Robot Overlord
• Posts: 158
##### Re: Calculating Sprocket For Treads
« Reply #1 on: March 18, 2012, 09:21:53 PM »
Technically you are using wheels you just have to look at it a little differently. The wheels just run on the treads. So to figure it out you need to use the circumference of the drive sprocket.

#### Mastermime

• Supreme Robot
• Posts: 316
##### Re: Calculating Sprocket For Treads
« Reply #2 on: March 18, 2012, 10:07:40 PM »
How would I calculate for the speed I need then? Say my treads were smaller, wouldn't that affect my desired speed?

Or do circumference of the treads not matter?

#### Soeren

• Supreme Robot
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##### Re: Calculating Sprocket For Treads
« Reply #3 on: March 19, 2012, 02:38:51 AM »
Hi,

I am a bit confused.  Will this formula still apply for finding the sprocket I need when I am using treads.  Velocity= Circumference*RPM.  Then solve for RPM.  Or does this only apply when using wheels?
It does apply, but the circumference used should be the circle of engagement of the sprockets.
You will probably have to calculate for the minimum and maximum circle (and then take the average), as the point of engagement is not really a point, but happens over a part of each cog as the wheel turns. If the wheel has seen some action, it will be easy to see, as the area will be "polished" by friction.

When I try and do this, I am getting a low number for the final RPM so I don't think I have the conversions, right?
It would be more informative to write the actual numbers you get.

Here is the info

Circumference of treads:69 in
Desired speed: 10mph or 10560 inches per minute
Drive Sprocket: 11 tooth
If you want to go about it from this info, you need to measure the length of track per cog and multiply by 11. Then multiply by rotational speed (RPM).

If each cog moves the track 5mm and the rotational speed is 500RPM, the resulting speed will be 2.5m/minute or 150m/h (0.15km/h)
Twice the track/cog or twice the rotational speed will give twice the speed and so on.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Engineering is based on numbers - not adjectives

#### Mastermime

• Supreme Robot
• Posts: 316
##### Re: Calculating Sprocket For Treads
« Reply #4 on: March 19, 2012, 07:19:17 AM »
Oh I understand.  Thanks for the nice answer.   It helps a lot.  Unfortunately I dont' have the tracks and drive sprockets yet for the treads.  They're still shipping.  Once they do come I will definitely apply the method in the first paragraph (seems a lot easier).  I have measure my track length using a piece of rope and wrapping it around where the track will go.  Very scientific of course     Luckily I have a few inches to spare with my track tensioner.

#### Mastermime

• Supreme Robot
• Posts: 316
##### Re: Calculating Sprocket For Treads
« Reply #5 on: April 07, 2012, 09:24:53 PM »
Ok the tracks and drive pulleys just arrived today.  Im going to post all the information thats needed for calculating the necessary sprocket.  What I have doesn't seem correct?  Where'd I go wrong?

Miscellaneous Info
Desired speed: 10 mph
Drive sprocket (on motor): 11 tooth
Motor RPM: 2600 RPM

Circumference of treads: 70 in
No. of teeth: 140

Drive pulley Info
Pitch diameter: 2.546 in
Number of grooves: 16
Tooth length: 3/16 in

Drive pulley*tooth length: 16*(3/16)=3

RPM*3=10560          RPM=3520

I believe I did something entirely wrong, but I don't know what.  I think it might be my understanding of what you meant by "length of track per cog", but I'm not sure.

« Last Edit: April 07, 2012, 09:29:06 PM by Mastermime »

#### Soeren

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##### Re: Calculating Sprocket For Treads
« Reply #6 on: April 08, 2012, 12:31:32 PM »
Hi,

Miscellaneous Info
Desired speed: 10 mph

Drive pulley Info
Pitch diameter: 2.546 in
The above will do:
Pitch circumference: 2.546" x Pi =  ~8"
16mph = 1,013,760 inches per hour = 16,896 inches per minute
Needed rotational speed of the pulley:  16,896 / 8 = 2,112 RPM (loaded speed)

Since I don't know if you have any gearing between pulley and motor, you'll have to do the eventual remaining calcs yourself.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Engineering is based on numbers - not adjectives

#### Mastermime

• Supreme Robot
• Posts: 316
##### Re: Calculating Sprocket For Treads
« Reply #7 on: April 08, 2012, 02:11:45 PM »
Quote
16mph = 1,013,760 inches per hour = 16,896 inches per minute
Did you mean 10 mph (10560 in. per min)?  If I used 10 mph then the rpm needed would be 1320 rpm.  If you meant to put 16 mph, why did you use that number?

#### Soeren

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##### Re: Calculating Sprocket For Treads
« Reply #8 on: April 08, 2012, 06:48:46 PM »
Hi,

Did you mean 10 mph (10560 in. per min)?  If I used 10 mph then the rpm needed would be 1320 rpm.  If you meant to put 16 mph, why did you use that number?
Oops... You see 10 miles is roughly 16 km, so I simply typed the wrong number and got the speed required for 16 mph. My bad and you're absolutely correct...
It should be 1,320 RPM
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Engineering is based on numbers - not adjectives

#### Mastermime

• Supreme Robot
• Posts: 316