Modular tadpole.

[pegasus]

Inspired by Emiel's tadpole design, I thought that I put a design concept I've had in my head for a long time on to paper and then into reality.
My idea is to build a suspension tadpole similar to Emiel's design incl, steering, seat and mid gear with electric motor,
so a single rear wheel, dual rear wheel , camper rear or cargo rear can be attached to this front.
I have a lot of 5/8 x 1/16 off cuts to be used as the front suspension frame and also some round tube suitable for the front boom.
It's not a urgent project, I have enough projects to try to finish for this and next year. Just something to slowly develop.

 

[stormbird]

DannyC will be along shortly to add his vote , right up his street that only 1 front end can and numerous uses by changing the back end.

Paul

 

[DannyC]

Sadly I have run out of legs (and room) for cycling contraptions. I am struggling with what I have already, let alone building more.
The spirit is willing but the body is past all hope I think.

 

[stormbird]

Sadly I have run out of legs (and room) for cycling contraptions. I am struggling with what I have already, let alone building more.

Says the man who is getting a pedal car ?

The spirit is willing but the body is past all hope I think.

I though this is where electric assist was deployed ?

Yes you need to sell the tadpole to free up some space , it will happen young Grasshopper just be patient

Paul

 

[pegasus]

The suspension frame will be made of 5/8 x 1/16 square tube, I done a strength test, jumping on the tube between 2 support, and it passed the test.
So on with the design.

I based it on Steins design with 20" front wheels.
The Stein trike has a well span of 780mm and so will mine, so the under suspension arm will be around 250-280mm? and the upper 200-220mm?,
The height between the arms 100mm? and the space between the frame support 120-150mm?, are the arms parallel?
The shocks, 150mm long?, gives a 30mm stroke?, how much suspension do that give? 350lbs?, in steins design the shocks don't line up with the tire track, pros and cons?
I thought using 4 x 8mm rod ends for each frame side and 2 x 10mm rod ends for wheel side, any other suggestion?

 

[Popshot]

30mm stroke will give a huge amount of suspension. Without a lot more measurements I can only guess but at least 4". There's a lot of leverage in that design. Again many more dimensions would be needed to calculate spring strength but it'll be fairly heavy. 350 would be a reasonable guess as a start point. You'll want to limit travel to a couple of inches or so via the spring weight or it'll roll like a ship in distress should you corner hard. The shocks not hitting the tyre are irrelevant to this design. No pros or cons as it affects nothing. It's the line through the top and bottom m10 rod ends that needs to do this. Your rod end choice is probably ok given your svelte build. I have bent cheap m10 in a similar but non suspended design but I'm hauling a lot of lard and having suspension will ease any loadings. Try to get the rod ends as far into their nuts as possible to get loadings into the tubes not the rod end itself and don't buy the cheapest ebay special rod ends. There's a big difference in rod end qualities. HT rod end casings over chocolate ones etc. 16 rod ends including the steering ones soon adds up to escalate the budget and buying cheap ones gets tempting. Dependant on exact design and amount of suspension the steering links may need misalignment spacers to cope with the range of movement asked of them. Thin housing rod ends sacrifice some strength for extra articulation. The steering won't need the strength but that extra movement may mean the difference between needing spacers and not. Try to get the inboard steering rod ends in the same vertical plane as the lower wishbone pivot and the arms parallel with it as this will stop bump steer.

 

[pegasus]

Thank Popshot,
Yes my thought was to buy cheap rod ends, I presume that the threaded part of the rod end is the weak point. I planned to weld a 12mm square x 15mm piece of steel inside the end of the 5/8 tube and then drill and tap a m8 tread into the insert to fitt the rod end. I could weld a high strength bolt to the insert and use a female rod end instead. An alternative is to use bronze bushes, 8 x 14 x 8 are very inexpensive and I have a suitable tube to fit in stock.
I prefer the rod ends because you can tighten them hard, but I presume you have to tighten a bronze bush just enough to eliminate any play.
I never even thought about the steering rods, but I can see now that it's preferable to run the rod on the same plane as the under arm and being of the same length. That ackermann geometry complicates the modular design, all designs preferable should have the same wheel base, hmm.

 

[undertoad]

I have run out of legs (and room)

Hmmm - Are we thinking about making space for another small-ish vehicle?

 

[Popshot]

Yes. The weak part is the rod end threads. Females are stronger by their nature but look out of place in such an environment as though they are standing the arms off. They tend to snap rather than bend which is probably worse. I've used split bearings in a similar application for the inner arm pivots and would work like bronze ones. Probably a good idea to ask Emiel what size and strength spec ones he used on his quad. They are males and have done many miles.