Hi all, first time here!
I’ve finally started working on my Wild Thumper 6WD project, however due to the amount hardware that will be used, I need to widen the chassis. One way of keeping the center of gravity in rough terrain in between the wheels’ ground contact is by moving the wheels further outside. However this is not possible with the front and back wheels as the compression spring limits how far apart they can be placed. (I’m rolling my own tension cable using 1mm steel wire, so that’s sorted)
So if I replace the compression springs of the front and back wheels with the same compression springs that the center wheels have, I can move them further out (using the outer most hole on the chassis)
So my question is, where I can I buy the compression springs that are used with the center wheels?
Unfortunately, we do not have any alternative suspension springs for the Dagu Wild Thumper Chassis, and I do not have any specific suggestions for where you might find something like that.
Also, please keep in mind that by widening the wheel base you will likely reduce how much payload the chassis can handle since that is limited by the amount of radial load the motor output shafts can handle.
Thanks for the response. The torsion springs (which I incorrectly mentioned as compression in the previous post) which I’m looking for are the same ones that are used for the center wheels, not alternative ones. So basically I’m looking for the replacement (acquisition) of the below springs:
Good point about the radial load; I didn’t take into consideration that the motors will have a limit. Would you have a theoretical figure on the maximum radial load the 6V 75:1 motors can handle?
To clarify, we do not have any of the Wild Thumper chassis springs available by themselves.
For the unmodified chassis, the maximum recommended payload is 5 kg (11 lb). We do not make the motors that are included with the Wild Thumper chassis, and we do not have maximum radial load ratings for them individually.
By the way, my mentioning the radial load as the limiting factor is a bit oversimplified. Widening the wheel base will change the dynamics of the suspension and the chassis overall. It is not immediately obvious how much of that will translate to added stress the motor output shafts, but anticipating some reducion in payload capacity and designing to maximize your safety margin there in response would be prudent.
If the torsion springs are not available for sale individually then it renders the whole approach void.
Basically what you’re telling me is that the payload limit isn’t stemming from the suspension system that chassis has but from the motors themselves; so if I need to exceed the 5kg payload limit, then I need to redo the whole suspension design to shift the weight away from the motor shafts. That might be a whole project on its own and probably even beyond my skill level atm. If I get around to doing it and succeed, I’ll post my approach here.
Thanks for your time and information Patrick
The Wild Thumper chassis is probably not appropriate for applications with payload requirements greater than 5kg. If that is the case and you plan to use a chassis with similar size motors, then at minimum you will probably need to implement some method of decoupling the weight of the chassis from the motor output shafts, such as through belts and pulleys.
To be completely honest with you, I don’t intend to exceed the 5kg payload limit by much. My initial estimates have put the hardware at slightly over 6kg. But I want to play it safe, which is why I originally wanted to strengthen the suspensions. However if the motors are rated for a max of 5kg, then obviously I do not want to even approach that limit so it’s either some hardware has to go, find a lighter alternative to the hardware, or as you said, decouple the weight of the chassis using your suggestions or things like flexible drive shafts or CV joints.
However you mentioned “similar size motors”; do the 25D motors that Pololu offers, have a higher max payload than the Wild Thumper’s standard motors?
We have not done detailed characterizations of the effects of radial loads on the performance and lifetimes of our gearmotors, but our general recommendations for the upper limits would 0.5-1 kg for the 25D Metal Gearmotors. As I mentioned before, we do not have maximum radial load ratings for the individual motors that Dagu uses in the Wild Thumper chassis, so I am not exactly sure how they would compare, but I suspect the limits for those motors (as well as other brushed DC motors around the same size) are similar.