Spartan Trike Project

[DaveJ98092]

Jan 11, 2016 14:57:59 GMT -5 dain said:

I've seen an electric power steering gearbox/motor used, they are high reduction and powerful. simply create a mechanical linkage that swings the motor/sprocket onto the chain drive for reverse, have it swing in a way where the torque gives you mechanical advantage as in once engaged it will have a tendency to stay engaged until turned off.

Other easy way to do it is a starter motor on a flex plate mounted somewhere in your driveline.

A few builders made a bracket with an electric motor and a few, like 4 wide, sprockets that when you pull the reverse lever it pushes down on the rear tire and the teeth of the sprockets bite into the tires tread and a switch is thrown to engage the power. But it will need enough travel so it does not hit the tire in a bump so swingarm mounted is my guess.

I will need to do this setup if I go with Suzuki Burgman 650 CVT power. There is no chain or belt to drive a reverse.

[Liteway]

Jan 11, 2016 9:59:22 GMT -5 captainamerica said:

Joel,
There is a reasonably good picture of it in my vehicle engineering post on the technical page, its been awhile since I've looked at it though. The only thing I wish was better is the turning radius for U-turns, turns like a truck, not sure why but my guess is the wheel base. I barely make a U-turn across three lanes.

Andrew

Turning circle is no mystery, as you said, wheelbase plays a part, the rest is pretty much determined by the angle you can cut the front wheels to.


gamedev.stackexchange.com/questions/50022/typical-maximum-steering-angle-of-a-real-car

[captainamerica]

Triplethreat,

While I agree in basic terms that this is true, its very theoretical. The picture shows an ideal situation where full Ackermann steering is used at max turn, the reality is usually going to vary where the two lines from the front wheels cross somewhere out in space and then there is some wheel scrub especially as speed increases. The second part is just based on what I have seen when my steering, my full lock is turned really far but the wheels just sort of scrub the ground trying to get traction to make the turn that is being requested of them. Adding castor or camber may help this situation but in my case castor is built in and the addition of camber destroys my tires. I will look into what my theoretical expected turn circle is and maybe when its warmer out I will do an actual parking lot test and see how close they are.

Andrew

[Liteway]

Dang, always more to it than you think.
Ever see a Bug EYE Sprite at full lock? Wheels looked as if they were near 90, must have a very impressive turning circle if the scrub you mentioned could be avoided. Bet on gravel they would just skitter straight ahead.

1/15. Not worth a new post, I need to correct this one. For some reason every time I think I know something, a little research proves I don't.
The turning circle of the 80" wb Sprite was over 31ft, actually slightly worse than a modern Miata, not so impressive for such a tiny car (44" track!). I think I had it confused with a Triumph Spitfire with a turning circle of 25'3". For prospective the the only modern? car that comes close is the Fortwo at 28.8. For a Corvette its 39ft!
Haven't measured mine, but I intend to, both as a theoretical diagram and actual, then post it on my build log.

1/17 Wrong again. 25'3" for Spitfire based GT-6. 24' for Spitfire.

[Liteway]

Jan 13, 2016 14:10:41 GMT -5 captainamerica said:

Triplethreat,

While I agree in basic terms that this is true, its very theoretical. The picture shows an ideal situation where full Ackermann steering is used at max turn, the reality is usually going to vary where the two lines from the front wheels cross somewhere out in space and then there is some wheel scrub especially as speed increases. The second part is just based on what I have seen when my steering, my full lock is turned really far but the wheels just sort of scrub the ground trying to get traction to make the turn that is being requested of them. Adding castor or camber may help this situation but in my case castor is built in and the addition of camber destroys my tires. I will look into what my theoretical expected turn circle is and maybe when its warmer out I will do an actual parking lot test and see how close they are.

Andrew

Not sure of what affect camber might have on turning radius, but I think adding caster has a negative affect. An extreme example would be a raked out chopper which has a ridiculously large turning circle.

To help visualize, imagine the kingpin angle fully horizontal instead of vertical. Steering input just results in the wheels cambering in and out, no steering at all.

Caster is the friend of stability and the enemy of steering responsiveness.

[noahkatz]

Andrew,

Very impressive work!

Question on your uprights - what's the purpose of the radial splits at the ID where the spindle will go?

Re turning radius, how about power oversteer?

[edit] Ah, the splits must be to allow a clean start to the cut.

Sept 22, 2015 15:04:49 GMT -5 captainamerica said:

...I like the performance of the welded parts and the cost so I am just keeping that design and making it the standard.

Have you done stress analysis of the upright at the weld?

Probably very low, but if you don't re-heat treat, the yield strength of 6061 T0 is 8 ksi and fatigue strength 9 ksi.

www.matweb.com/search/DataSheet.aspx?MatGUID=626ec8cdca604f1994be4fc2bc6f7f63 (handy site if you weren't already aware)

[captainamerica]

The radial splits are a manufacturing thing, basically every punch through the waterjet has to do cost about $30 which is one for every pocket. So it was much cheaper to just create the like channels to each of my pockets from the main pocket and weld them together when the bearing carrier gets added in. It dropped ~$100 off the cost of each piece.

Power over steer only really rears its head in the wet, in the dry I have a bigger problem with powered understeer, the car will just drive right through the front end inputs straight through a corner. If I popped the throttle before I approach the turn it might cause a power slide, but I spent quite awhile in a parking lot getting a feel for this at the end of the summer and the trike just wants to push through the front, more front camber might help this as well but the tire wear makes it reasonable only for special occasions like auto-cross.

Turning radius isn't amazing, once the sun is out I plan to do some testing in that regard, driving the average roads I have no issues but U-turns are a pregnant dog, from the left turn lane on a 6 lane road I usually barely miss the side walk on the far side, so that would be about a 40ft outside to outside distance, 20ft turn radius. I feel like this being in the 15ft range would be about right.

I am aware that the welding can cause problems but the total weight of the system makes the upright rather overkill for what its doing. I keep a reasonable eye on the uprights, look for weld cracks and what not, but haven't had any issues so far after 4500 miles. The new ones will have a lip on the bearing carrier which should stop the wheel from flying off if the weld were to completely separate, probably wouldn't feel good from the drivers position but it should still be controllable. Worst case scenario happened early last summer after sun down, driving across a bridge under construction, forgot about the construction, hit a 1" steel plate covering new concrete at about 45mph, launching the front of the trike a few inches in the air because my front suspension is much to tight and then by the time I realized what had happened I was into the next one for a second hit, came home a little rattled but everything looked good on inspection. The front suspension feels great on a nice smooth corner but it feels like its basically solid when you hit a bump. Need to do some work on that this spring.

-Andrew

[noahkatz]

Actually I meant intentional power oversteer to help out with those U-turns.

The good thing about fatigue failure is that cracks grow over time, and with as much material as you've got there's plenty of leeway.

[captainamerica]

Sorry my response was ambiguous, the powered understeer is actually what happened when I tried to pop the rear end out intentionally. I think if I hit the throttle and then turned I could probably upset the balance to make it happen but in my parking lot experience trying to get power oversteer mid corner by overpowering the rear wheel caused the thing to just drive through the front wheel inputs, its a very strange feeling. I will have to work on this technique in the future.

[Liteway]

 Captain.

I figure (possibly wrongly) that the same chassis theory holds true for trikes as it does for quad vehicles; that is, the end with the  most roll resistance is going to push.
To make a car under steer, you stiffen the front,  for oversteer, stiffen  the rear. As a trike has essentially no roll resistance at the rear, it's going to push at the front. Unless balanced with the throttle, mine under steers and I think  that   is to be expected in a tadpole.

However, what you are describing, with fronts able to get little or no bite  at full lock at low speeds under throttle , is not normal.

For instance, if you are entirely out of the vehicle, pushing it about the garage at full lock, do the tires scrub? A little is normal. A lot is not.

I know you are knowledgeable about ackerman principles, but have you physically checked the angles of the front wheels at full lock to see if they match the spec you intended?

At one point  before I had this angular difference set up properly, the trike behaved exactly as you describe.  At a later date, after modifying the front end, I got the toe set wrong and excessive scrub resulted then as well.  

 This could account for your  rapid front tire wear and heavy under steer.  Of course  we don't  do much driving at full lock, but if your alignment is off there, it's probably not correct at lesser angles either.  I'm betting(again could be wrong) that your caster or camber are not off enough to cause what's happening. With your vehicle's light weight, your tires should wear  far less than  if mounted on a 3000lb car.

[dain]

You've probably got all of 10 lbs/piece on those front tires... stiffening/softening your suspension front to rear won't do anything for you, one thing you might try is switch to a rounded motorcycle rear tire, it will narrow up your contact patch giving you much less resistance to turning. ALSO, when your chassis leans and the rear cambers with the chassis you will still be using the treat of the tire instead of the sidewall. I use a car tire on the rear of my trike because it was easy, it is currently a low performance vehicle, and I have 400lbs of batteries stacked directly between the front tires so I have zero issues with understeer. 40/60 front to rear bias on your vehicle would be about as much as you could hope for, i'm guessing you are closer to 30/70 now with a pilot.

[Liteway]

Your 30/70 weight distribution estimate is way off. In previous discussions with the Captain on this I believe he said he had more than 55 percent up front. Jives with mine which is 52.5/47.5 , Measured, not estimated.

Having used a 170/55 motorcycle tire on the rear 3000 miles, and a 175/55 car tire for 6k, I think I can speak to the difference it makes in dynamics. Very little. The bike tire did wear 3 or 4 times as fast. With the power of Captain's trike a bike tire would not last long for 2k.

[DaveJ98092]

It is very rare that a tire rolls over onto the sidewall now days. In the old bias ply days it did happen. And if you have too much positive camber it could tuck the tire tread under. Even with the use of a flatter tread Car tire on mt scooter, it never rolls onto the sidewall even when I am SCRAPING the centerstand and front plastic. I have been running a Car tire on the rear of my scooter for 8 years now and there are videos that show the tread never rolls on to the sidewall.

I think putting a motorcycle tire on the front will cause it to lose traction much faster in a corner.

[dain]

hmmmm... with the power of a bike, the bike tire wouldn't last long - Want to rethink that triplethreat? A tire designed for that exact engine will not work is what you are saying. If you aren't constantly doing burnouts a rear tire can last for a long time - the one currently on my Hayabusa I put on 6k miles ago and it still has plenty of tread.

You guys are both missing my point - the motorcycle tire is to go in the rear, not the front. The body does in fact roll and the rear tire will roll with it putting its pressure on the sidewall.

You are also high if you think his weight distribution is 55% up front.

[Liteway]

Feb 5, 2016 13:39:10 GMT -5 dain said:

hmmmm... with the power of a bike, the bike tire wouldn't last long - Want to rethink that triplethreat? A tire designed for that exact engine will not work is what you are saying. If you aren't constantly doing burnouts a rear tire can last for a long time - the one currently on my Hayabusa I put on 6k miles ago and it still has plenty of tread.

You guys are both missing my point - the motorcycle tire is to go in the rear, not the front. The body does in fact roll and the rear tire will roll with it putting its pressure on the sidewall.

You are also high if you think his weight distribution is 55% up front.

No, I'm not high, and that is a rude thing to say, implying my thinking is defective. Maybe you are just trying to be funny. Let's try to keep the discussion on a technical level, shall we. (Edit 1/28/17:
Apology to Dain for this humorless overreaction.)

I will admit I have not weighed the Captain's trike at each wheel, and I'll leave that right there.
I have weighed mine, and its configured much the same as the Captain's on a slightly smaller scale.
Using a common bathroom scale at each corner is not the most precise way to do it, but keeping the trike as level as possible, with me aboard and my son watching the scales, I doubt the results are far from real.
RF 192
LR 189
R 344

52.5/47.5
Captain's trike has a longer swing arm, shifting mass slightly farther forward, so his 55% forward seems reasonable to me.

I am curious, what would lead you to believe his trike has only 30% of its weight forward when its quite obvious the two principle masses, the driver and the motor are centrally located within the wheelbase?

Rear tire wear on a motorcycle is not comparable to rear tire wear on a tadpole trike using a motorcycle tire.

Motorcycles have a high center of gravity, and the weight transfer under acceleration gives them much better traction. Static weight bias to the rear is greater too, resulting in a lot less wheel spin.
Wheel spin erases rubber fast.

Motorcycles spend part of their time banked over, evening out the wear somewhat, while the trike flat spots its tire quickly.

The thrill of drifting a trike through a tight corner is hard to resist, but its hell on tires. Doubt you do much drifting on the Busa.

I am speaking from experience, not conjecture. The IRC Sport bike tire I had on my trike was near toast in 3000 miles. The captain's trike is larger and much more powerful than mine. I would expect him to not get that far on one.

[DaveJ98092]

Video's of a Car tire on the back of a TWO wheel bike in the corners. Notice how the tire never rolls over on the sidewall. In The Captain's trike, it would never get this much side loading so it also should NEVER roll over.

1. www.youtube.com/watch?v=gZKhoFbL7Fo

2. www.youtube.com/watch?v=PZ_d5IIdRZI In this video at about 1:40 it shows that the Car tire still has more tread on the ground than a motorcycle tire would. This is a HEAVY rider and he is cornering kind of hard too.

[captainamerica]

Alright gents lets keep this calm, Dain, as the newbie here you would be wise to listen to triplethreat his grasp of the concepts of vehicle handling has been spot on in the conversations I have had with him. The true CG according to the scales on my trike with me in it, weighing in at just under 1000lbs, is 300 on each front wheel and 400 on the rear bringing an almost perfect 60/40 weight bias to the front. The issue with running a motorcycle tire on a trike, which I believe TT was alluding to is that the motorcycle tire is meant to lean when you corner to take the load at the optimal point and it has the benefit of spreading the wear across the whole radius, with non-leaning trikes you would end up scrubbing the smaller contact surface and and only ever use the center of the tire. It also really won't help when you try to power through a corner unless you want to break the rear end loose. In my drag strip videos you can see that there is no traction at the start even with a car tire on the rear with the amount of torque I have in first gear, drop the clutch to slow and you stall, drop it to fast and you burn out. It may be the exact engine combo but it is not the exact vehicle combo.

The CG of my trike is literally in my pelvis when sitting in the vehicle, so I don't have much of an effect on the weight balance in or out of the car. The thing you have to remember about my trike if your having difficulty wrapping your head around it is that the chassis is around 300lbs and I protected myself it 12 gauge sheet steel all around the driver, the battery is in the nose cone with all the brakes components, steering rack, front suspension for two wheels, and so on. This is then backed up in the rear by one of the lightest power to weight ratio engines in the world hooked to an aluminum swing arm and wheel. In general I find it more difficult to get weight over the rear and would tend to easily believe anyone who say they are forward weight biased.

To answer TT, the wheels do scrub excessively at full lock, it makes it almost impossible to move by hand. Even though I know they aren't it feels like they are turned at 45 degrees to the direction of travel. It also feels like they turn past some center point when I go full lock, somewhere between 90-100% turn its like the castor goes from wanting to go straight to wanting to dive more into the corner. I may need more ackermann difference, I'll have to borrow a digital angle sensor from work and see if I can sort out the actual ackermann angles that got built into the thing. The front wear only occured when I had what I would call excessive camber (2.5-3 degs) and it was easy to see, after 500 miles I was about half tread on the inside and still had those little rubber hangers that come on new tires sticking out on the outside of the tire. I adjusted the camber to around 1 degree and haven't seen almost any wear after another 4000 miles. There is also the humorous side of this that the tire loads are so low compared to their rated load that I can't actually tell when the tire is flat, have probably put about 1/4 of my road miles on the thing with all the tires having zero pressure register the gauge when I remember to check. The benefit here is that I have run flats at $30 a wheel

[Liteway]

Ha! I'll have to try that run flat business.

The over center feel you get in your steering near full lock, where it wants to do the opposite of self centering, has to do with the flattening of the angle formed by tie rod, the steering arm and the kingpin axis near full lock. I think trail and caster  may figure in as well. I know exactly what you are talking about because mine does it too. I do not know the exact cause, but I'm pretty sure I cannot fix it, as about the only thing I can do to affect it without starting from scratch is change the angle of the steering arms. Their present angle and length were selected to mix scrub free turning with zero bump steer and provide the desired amount of lock with the limited range of arm motion at the controls. Any change now would affect those priorities.
Its annoying but I don't think it's dangerous as the effort to pull back from full lock is not much.

Could be we have been overzealous in maximising lock, and the problem could be solved by reducing it, but I would rather retain the sharpest turning possible.

If you were to look at a diagram of my steering, It shouldn't work worth a dang as it is far from conforming to ackerman's principles.
My unconventional steering, which replaces the fixed steering rack with a tie rod that moves fore and aft about 5/8", throws addition complications into the already complicated world of front end geometry.

I made a lot of plan view diagrams on paper (dang my lack of computer skills)with changes to the steering arms to see what the effect was on the front wheel angles at various stages of lock. Those did not take caster into account, so they did not fully reflect reality, but it got me close and some experimenting with hardware after that got things working pretty good.
reversetrike.proboards.com/thread/606/stick-steering-diagram-installed-trike


One thing you can do, to temporarily establish what angles work to reduce scub, is adjust them by changing the toe alternated with out-of-the vehicle push tests. Crude but effective. If you cannot push it at all, you are way off.

[dain]

I stand corrected I can't argue with numbers.

[extremetrikes]

Feb 18, 2013 11:31:39 GMT -5 stretchmobileski said:

I don't know if you are aware of these nifty little tilt steering units. Makes your steering set up much more convenient. Available in left or right release, raw, powder coated and chrome. Sandrail suppliers for under $100.

Really glad I read this! Thanks for the info