Let's Make Robots!

"Wild Thumper" 6WD all terrain robot chassis

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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.

6WDnew6.jpg

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.

6WDnew5.jpg

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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I must say that the Wild Thumper platform is a wonderfully well thought out system!  I cant wait to buy one for myself!

 

mekkatronix@yahoo.com

I am trying to assemble the motor housing but I am having difficulty in getting the parts in India. Can you suggest a cheaper alternative to the DC Motor housing?

OddBot's picture

The kit come pre-assembled.

What do you mean "I am trying to assemble the motor housing"?

I am trying to buy the parts. The kit comes a bit costly for me here in India. I really wanted to work with the platform and a major obstacle is the motor housing since I am not able to find any alternative to it. Anything you can suggest?

OddBot's picture

Here is the tutorial for the original prototype.

http://letsmakerobots.com/node/5155

Today's adventure was increasing the tension on the suspension to better handle the weight being carred by The Mystics. The Mystics are described here. If you take a look you will see they are carrying 20 Ah of LiPo batteries and an ITX PC. They weigh about 6.5 kg (just over 14 lbs). With that weight the wheels splayed quite a bit. 

Adjusting the suspension is not a trivial task. It requires disassembling quite a lot of the chassis to get at the tensioning springs. I thought I would share my experience to help others. 

Find the diagram that came with your chassis or on the web showing how to adjust the tension. The diagram makes it look easier than I found it to be. 

Tools: 7mm open end / box wrench, #2 Phillips screw driver (at least that is what I used), small ratchet driver with hex adapter the same as used for the wheels. (I used a T15 torque head since I did not have a metric hex wrench that fit.)

The ratchet driver has to fit in the baskets and reach the hex head machine screwes. You DO NOT want to attempt this just using the hex wrench that comes with the chassis. It will take forever with just the hex wrench. 

  • Disconnect the wires from the terminal strip. Having the end wheel baskets flopping around while working on the center basket is painful. I tried and finally disconnected the wires. 
  • I left the wheels mounted. They provided a stable base for working on the unit when it was tipped on its side to get to the screws and nuts. Post a reply if you tried it without them, please.
  • Use the ratchet and wrench to remove the two machine screws and lock nuts on one end. 
  • Repeat for the other end.
  • In the same manner, remove the two baskets from the center section. 
     
  • On one end basket remove the four screws that hold the motor mounts. The motors will drop out. 
  • Adjust the tension spring. Driving the screws back in takes a lot of torque. I used an electric screwdriver and it still was difficult. (I could not tell if the screws are supposed to go in radially or in parallel with the center hole. OddBot?) 
  • Repeat for the other end. (I shortened the cable on one end because I was having problems with the wheels tucking under when 'spinning' on grass. But I could not shorten the other end and get the motors back in with the increase tension.)
     
  • Remove the four screws holding the motors into the center mount.
  • I did not disconnect the springs from the mount. It was a bit of a challenge this way but it did work. I was concerned it would be a real challenge getting them connected again given they would be under tension. 
  • Move the springs to the hole that you want. I found that running the screw into the gromet helped with this since it improved the angle of the screw into the motor.

Now comes the real challenge - getting it back together. The factory build has the screws between section in the inner and outer holes of the basket. Getting the lock nut onto the hole that is deep inside the motor mount is really difficult. I managed it with mounting the baskets to the center section. But at one point I suggested my wife leave the room since she was on the phone with her mother and my words were not always something my mother-in-law should hear from me. For mounting the end motor mounts I used the center hole and the outer hole of the motor mount. That is the inner hole in the basket. 

  • Push a screw through outer or center hole of a basket. 
  • Slide the plastic plate over the screw using the same hole!
  • Be SURE to put the plates between the baskets and not inside. I caught myself starting to do that twice.  
  • Somehow get the lock nut on the screw. I managed on the center section to get it on the deep hole by sliding the screw almost out of the center sections hole. Then, using a needle nose pliers held the nut in position and, using my fingers, turned the screw until it caught. Not easy! On the end sections I used the center hole and could get my fingers into the mount to hold the nut. It worked better. 
  • Snug down the nut but do NOT torque it all the way down.
  • Repeat for the other hole which is a lot easier since you can reach in with your fingers to position the nut. 
  • Again, repeat for all the other baskets. 
  • After the chassis is reassembled check the alignment of the baskets and mounts. They may be cocked off a little bit. Align them and NOW torque down the screws and nuts. 
  • Reattach the wires. 

It took me about three hours to do this and I have at least 2 more chassis to do. I may get a fourth chassis for next years challenge. 

Hope this helps somone attempting this.

Rud

 

OddBot's picture

I admit, the only problem with this suspension design is the necessity to disassemble the entire chassis to adjust it. Alternatively you would need to drill some 6mm (¼ inch) holes in the chassis so you can get a screw driver directly above the screws on the motor housings.

It sounds like you do not have the right tools for the job. Our workers use an allen key and a small socket thats been welded onto another allen key but I've also done the job just using long nose pliers and an allen key. It took less than an hour.

 

Getting replacement tires or wheels is a real hassle. I visited two local shops but nothing they had would work. Searching the RC website is a challenge because they do not list by dimensions.

Are these wheels for a 1:8 scale RC truck? What are the hub dimensions? 

OddBot's picture

There are shops that sell replacement wheels.

Robot Shop: http://www.robotshop.com/dagu-all-terrain-wheels-four-pack-3.html

SparkFun: https://www.sparkfun.com/products/10555

Pololu: http://www.pololu.com/catalog/product/1555

There are probably some other shops as well. You can also buy replacement brass adaptors that allow the wheel to mate to the motor drive shaft at some of these stores.

The wheel is a standard RC type but I could not tell you which one as I haven't played with RC cars in the last 20 years.

mitch.tolson's picture

I've spent quite a bit of time looking around on the internet for some CAD models of the 6WD Chassis. Are these made available anywhere? I've found the drawings with basic dimensions, but it would be a huge time saver not having to remodel everything.

Thanks,

Mitch