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Track Powered Car

09/19/2016 12:32 PM

Hello!

I am designing a car (Buggy) with tracks (like a skid steer) and I am not sure of the total torque required to my HYD motor. I made some estimations if it was a "wheel" based car and assuming some road conditions (I selected several from 0.4 - 0.001 constant of friction) and came up with 1500 lb-in per motor (assuming that there is only 2 wheels since the track will only have 2 motors on each track). Assuming this is correct, how accurate is the wheel based calculation to a track system? Should I increase the torque needed by a certain amount to be on the safe side?

Vehicle Specs

Total weight: 5000 lbs

Max Speed: 7 mph loaded

Max grade : 25 degrees

Road Conditions: Gravel, loose dirt, concrete

Thank you very much in advance!

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#1

Re: Track Powered Car

09/19/2016 2:07 PM

I'd look at some equivalent vehicles already on the market and follow their lead.

They probably have engineers who have already done these calculations.

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#16
In reply to #1

Re: Track Powered Car

09/21/2016 4:57 PM

You mean like this??

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#2

Re: Track Powered Car

09/19/2016 2:30 PM

There needs to be some further information, such as track drive sprocket pitch diameter, motor rpm limitations, and ratio of any reduction gearing.

One intermediate calculation will involve 5000 sin 25º ≈ 2113 lb.

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#7
In reply to #2

Re: Track Powered Car

09/19/2016 6:48 PM

I am using a 7.14 in dis sprocket driving the track. I already too into account the angle for the additional torque requirement. Rpm on the motor is about 160 RPM so that I can get 7 mph. I am not thinking on using a gear reduction gearbox since I can find a Low Speed High Torque Motor to use. I only using one HYD motor per track and they will be controlled with independent sections of a pump. not doing hydro stat pump, open loop with electronic controls.

Hope this makes it easier to understand what i am trying to do.

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#9
In reply to #2

Re: Track Powered Car

09/19/2016 9:39 PM

Given your 2113 pound estimate I am coming up with a per track axle torque of ~ 750 Ft/Lbs per track to get 7 MPH on a 25 Degree slope and a power input of ~48 HP gross as bare minimums.

That seem reasonable to you?

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#10
In reply to #9

Re: Track Powered Car

09/19/2016 9:55 PM

That seams a bit too high, is that because of being a track system? I will attach my excel sheet tomorrow in how I got to the numbers I got. Please remember those are based on a wheel system not tracks. I have been doing those for a long time and everytime I have had success!

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#11
In reply to #9

Re: Track Powered Car

09/20/2016 1:23 AM

For static holding force only, I'm coming up with 296 lb-ft per track. For HP @ 7 mph horizontal (287 ft/m vertical), I get 43.5. These numbers are rounded off, of course, and I may recheck them tomorrow.

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#14
In reply to #11

Re: Track Powered Car

09/20/2016 5:49 PM

That seems about right. I've been around hydraulic systems and their calculations Vs real world results when working with likely less than perfectly match pump valve and motor components to enough to know to always round off high and estimate a bit higher yet.

So 43.5 + ~10% would land within working range my 48 HP estimate.

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#15
In reply to #14

Re: Track Powered Car

09/20/2016 6:10 PM

I didn't specifically account for efficiency, which could correct my estimate even closer into your range.

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#12
In reply to #2

Re: Track Powered Car

09/20/2016 8:52 AM

These are my calculations (If using wheel based vehicle equations). Also, these are per track so total HP needed would be times 2. What am I forgetting that my HP needed seems to be lower than what your coming up with.

TTE = RR + GR + FARR [lb] = GVW [lb] X CrrGR [lb] = GVW [lb] X SIN(Ѳ)FA [lb] = GVW [lb] X Vmax [ft/s] / (32.2 [ft^2/s] X ta [s])
TTETotal Tractive Effort [lb]RRRolling Resistance [lb]GR [lb]Grade Resistance [lb]FA [lb]Acceleration Force [lb]
RRForce necessary to overcome rolling resistance [lb]GVWGross Vehicle Weight [lb]GVWGross Vehicle Weight [lb]GVWGross Vehicle Weight [lb]
GRForce required to climb a grade [lb]CrrSurface FrictionѲMaximum incline angle [°]VmaxMaximum Speed [ft/s]
FAForce required to accelerate to final velocity [lb]taTime required to achieve max speed [s]
TYPE OF ROADRR [lb]GR [lb]FA [lb]TTE [lb]Tw [lb - in]RPMmotor shaftPower Required [hp]

These are per track, it needs to be multiplied by 2

Car tire on lose sand600845.237127.5361572.7735614.799164.7714.680
Car tire on solid sand, Gravel loose worn,
Soil medium hard
120845.237127.5361092.7733901.199164.7710.199
Cal tires on cobbles60845.237127.5361032.7733686.999164.779.639
Car tire on gravel40845.237127.5361012.7733615.599164.779.453
Car tire on asphalt40845.237127.5361012.7733615.599164.779.453
Car tires on concrete35845.237127.5361007.7733597.749164.779.406
Low resistance tubless tires4845.237127.536976.7733487.079164.779.117
Tw = TTE [lb] X Rw [in] X RF
TwWheel torque [lb - in]
TTETotal Tractive Effort [lb]
RwRadius of wheel [in]
RFResistance Factor
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#13
In reply to #12

Re: Track Powered Car

09/20/2016 1:42 PM

It is quaint to see imprecise numbers carried out to three decimal places. GIGO at its best.

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#3

Re: Track Powered Car

09/19/2016 2:36 PM
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#4

Re: Track Powered Car

09/19/2016 4:18 PM

Are you going to make scale models, or go full scale right off the bat?

Can you test with electric motors?

Pretty much, IHNI, but it seems to me you mentioned 2 motors per track, is that right? Four motors in all, but how do you ensure they are in sync?

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#5
In reply to #4

Re: Track Powered Car

09/19/2016 4:21 PM

By the fact that they are connected to the same track?

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#6
In reply to #5

Re: Track Powered Car

09/19/2016 4:36 PM

OK, but if one is picking up more HYD than the other, does not one become the driver and the other the driven?

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#8
In reply to #5

Re: Track Powered Car

09/19/2016 6:51 PM

they would not be connected to the same track, each motor has a sprocket connected to their respective track. Using a 7.14 diameter sprocket and each motor is being supplied with oil by independent sections of the pump electronically controlled.

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