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"Wild Thumper" 6WD all terrain robot chassis


Vendor's Description: 


It's Here! Now with Video of it in Action on dirt using 34:1 gearboxes and new videos going down and up stairs and over snow with 75:1 gearboxes.

6WD_Silver_chassis_3__small_.jpg

Now available in silver!

Designed originally here on LMR specifically for robots, this 6WD chassis has wicked spiked 120mm dia. wheels and an anodized aluminium chassis made from 2mm thick plate. The chassis has 4mm dia. holes punched every 10mm to allow easy mounting of PCBs, servos etc. All nuts, bolts and screws are stainless steel. Brass fittings and suspension springs are nickel plated.

Two chassis segments between the wheels have been designed to hold 7.2V sub C battery packs (not included) as used in many RC cars. A total of 4x 7.2V battery packs can be fitted if necessary. These batteries are ideal for driving the 6V motors as well as inexpensive linear regulators to supply 5V.

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These photos show how even with one wheel resting on a large LMR mug (115mm high) all wheels are still touching the ground. It may not be a rock crawler but that's awesome for an off the shelf robot chassis.

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Ground clearance with the suspension lightly loaded is 60mm which is almost half of the total 130mm height when the topdeck is mounted on 25mm spacers.

6WDnew3.jpg

As you can see in this photo, with the top deck fitted you have a smooth deck to mount equipment on even when the chassis is flexed. Mounted on brass hex spacers, the top deck gives you room underneath to hide cables and PCBs to give your robot a cleaner more proffesional finish.

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The suspension for the front and rear is a single torsion spring. As the motor housings are connected to each other and not the chassis the front and rear can roll freely with the spring supporting weight and absorbing shock.

The steel cable is used to limit spring travel. The motor housings have 3 holes for each allowing spring tension and travel adjusment depending on the weight of the robot. Rubber grommets are fitted in the spring mounts to eliminate play while allowing the motor housing to roll.

The center suspension is similar but has 2 springs. Each spring connects from the motor housing to the chassis keeping the robot upright.

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The 6 powerful geared motors have steel gears and are fitted with powerful magnets to provide high torque. Top speed is about 6.6km/hr. These motors have a maximum stall current of 5.5A each so with 3 motors per side wired in parallel a dual "H" bridge rated for at least 17A per channel is required.

Rated voltage: 6V DC (min. 2V Max. 7.5V)
Stall current maximum 5.5A
No load current per motor is 350mA
Motor RPM is 10000 +/- 5%
Gearbox ratio is 34:1
Output shaft speed is 295rpm +/- 5%
Stall torque is 4Kg/cm

A 75:1 gearbox is now available!
This gives a top speed of about 3Km/hr and a massive stall torque of 8.8Kg/cm per wheel!!!

The chassis comes pre-assembled and weights 2.6Kg. Shipping cost to America or Europe will be approximately $48 USD.

Now available in 2 colour schemes:
Black with metallic red rims
Silver with chrome rims

Here is a preview of the 4WD version:

4_wheels-1.jpg

 

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Stripped out SPI stuff again to return to state I had before. Have this crazy issue, maybe the SPI library pin assignment have done some damage but I don't really think so. Right side works great, pwm forward and reverse. Left side forward works with pwm, but reverse will only start at full throttle, nothing in between.  If I switch the logic for LmotorB and LmotorA, then reverse will work fine with pwm, but forward won't work at all! edit: looks like PWM is not actually working, just toggles. Interesting, I PWM on unused pins such as D9 and D10 won't work within this sketch, only toggle at 255, but will output pwm from a standalone sketch.

 

 

       switch (Leftmode)                                     // if left motor has not overloaded recently

        {

        case 2:                                               // left motor forward

          analogWrite(LmotorB,0);

          analogWrite(LmotorA,LeftPWM);

          break;

 

        case 0:                                               // left motor reverse

          analogWrite(LmotorB,LeftPWM);

          analogWrite(LmotorA,0);

          break;

        }

 

If the PWM is not working then it is possible that another library is using the same timer and has disabled PWM.

What libraries are you using? Most Likely you will need to use another Arduino as a master and set the Wild thumper up as a slave so you can have more timers.

I see in another post the suggestion to replace the existing wheels with smoother wheels when running on grass because the traction on the Wild Thumper wheels hinders turning. 

Is it correct that the wheels are for 1/10 scale RC given that the hex wheel mount is 12mms? 

I did a quick look for replacement wheels but the 1/10 wheels all seem smaller in diameter that the Thumper's wheels. Any suggestions on finding smooth wheels of the same size? 

I am wondering about replaceing just the center wheels with smooth treads. Since they are dropped lower than the end wheels maybe that would reduce the traction enough to turn more smoothly on grass? 

Thanks, Rud

The tire tread was chosen to give maximum traction in loose dirt, gravel and mud. Unfortunately this can be too much traction for grass and carpet.

Replacing the center wheels with smooth tread would be the worst possible thing you can do!!!
The middle wheels need the most traction for turning.

It is the front and rear wheels that drag sideways when turning on the spot. I would suggest simply cutting the spikes of the front and rear wheels with  some side cutters, nail clippers or scissors. If necessary adjust the steel cables to pull the front and rear wheels up higher and make it rock more.

I am using the Wild Thumper 6WD in the NASA Sample Return Robot Challenge. It takes place this June. I have two chassis with two more on order. The robots will have a lot of equipment on them so the weight distribution is important.

I notice with both my chassis that there is a slight tilt from one end to the other. On the slightly higher end the wheels tilt in just a bit more than those on the other end. The occurs even on the chassis that is currently my prototype that has an embedded PC, 12840 mAh battery, and some other lighter equipment installed. 

Is this tilt intentional and why? I am wondering if it is to aid turning in place by keeping the weight mainly on the center wheels (which I know are mounted slightly lower than the end wheels) and the wheels at the lower end. That would cause the Thumper to pivot more on those wheels than the more lightly loaded ones. 

Assuming this is intentional, is it meant to give the Thumper a front and back, if only slightly?

The basic issue is whether I should avoid putting more weight on the tilted up section?

I think these chassis are going to do very well in the competition, any failure is going to be mine with software and the equipment added to the robot. 

Thanks, Rud

The middle wheels are intentionally lower to reduce the drag on the front and rear wheels when turning on the spot. By adjusting the cable tension on the front and rear wheels you can increase or decrease the amount.

If your weight cannot be centered then you can move it more to the back (you decide what is the back) and adjust the steel cable at the front to lift the front wheels higher. This will cause it to drive around on the middle and rear wheels with the front wheels in the air.

The potential advantages of this configuration is that it will turn easier on just 4 wheels and with the front wheels raised it may be able to climb over bigger objects without just crashing into them. A potential disadvantage is that it may just fall over backward if the object is too big and in loose boggy conditions your weight is only spread over 4 wheels instead of 6.

Hey!
When I have the same PWM on both sides of motors, it's not going perfectly straight. Instead, it's slowly turning to one side over time.
Is this normal and how do I fix it? Just by trying to balance the PWM?

Yes it is normal with any robot chassis using brushed DC motors because no two motors spin at the same speed unless you use a feedback loop. The best way is to adjust the PWM of the motors but you need a feedback loop if you want good accuracy. Normally encoders are used.

DAGU do produce motors with encoders to suit the Wild Thumpers but so far the distributors have not been interested in stocking them. If necessary you can buy them directly from DAGU by contacting Claudia.

Are the motors with encoders that you mentioned similar to Pololu's 25D54L with CPR encoder? Can I replace the supplied motors with Pololu's motors?

They are similar to the pololu motors but are custom made to have more power.