Re: [CAD_CAM_EDM_DRO] Re: Problems in Timing Belt drive system in 6WD robot

Hi Doug,

I just got this reply!

I'm not following your logic. One belt on each side, the both go
forward to move forward. The split the load of the 'bot. I'm not
planning on locking one side to turn (like a tracked vehicle) , the
sides run slightly different speeds to make a gradual turn, or the
opposite direction to spin in place. Ideally each wheel axis would be
perpendicular to its arc, however as the outside wheels are nearly on a
square, they are fairly close. The center wheels are also on their arc,
so not too much scrubbing sideways.

4-wheel Ackerman steering would of course help! But did you see the
video of DPA's 'bot spin!

Alan KM6VV

On 1/26/2013 11:13 AM, Douglas Pollard wrote:
> I don't know for sure as I am have trouble picturing exact;y whats
> happening there but you have one belt pulling forward and one pulling
> backward. it would seem that both Belts have nearly dubble the load on
> them. It also looks like if both sides are pulling forward at the same
> speed each side has only half load on it??? If you lock one side the
> other side has to pull the whole vehicle around with that one side being
> pulled forward and at the same time while pivoting the other side is
> being physically driven sideways on the forward section and the other
> direction on the after section. I suspect the load on the pulling belt
> might be two to three or four times as Great. One way or the other
> turning increases the load on the belt seems to me. This is the
> advantage of having steering wheels, it takes much less power making
> turns. Doug
>
>
>> John Dammyer wrote:
>>> Hi John,
>>>
>>> I disagree. The principal of independent drive to both sides is used
>> pretty
>>> well all tracked vehicles. Just watch a dozer or tank turn in place with
>>> one side turning one direction while the other side turns the other.
>>> Control is often with two levers, one for each side, forward and
>> backwards.
>> No, a dozer or tank has a strong tread that handles the slippage when
>> turning. If you've
>> ever seen a dozer turn in soft soil, it churns the ground mightily as it
>> turns, due to
>> the sideways slippage of the front and rear portions of the tread. They
>> only
>> drive the tread from the rear axle, the front is an idler.
>>
>> The problem with this vehicle is all left wheels, and all right wheels,
>> are rigidly
>> synched by the belt. When turning tightly, the middle wheels are closer
>> to the
>> center of the turn, and should not be turning as fast as the front and
>> rear wheels.
>> When turning on its center, the center wheels need to turn MUCH less
>> than the
>> outer ones.
>> Why does this vehicle need six wheels? Try tying the suspension up with
>> wires to unload the center two and see how it turns.
>>
>> Jon
>>
>>
>