[DRIVING] VX220 with Tesla SDU

[Pete9008]

Looks great
Batteries couldn't be a better fit for the space!

[elShankos]

Awesome project! Thanks so much for posting all of this - helps a lot of us out to be able to see what you are doing

[catphish]

Awesome project! Thanks so much for posting all of this - helps a lot of us out to be able to see what you are doing

Thanks!

Please note, the main thread for this project is at https://www.diyelectriccar.com/threads/ ... du.205616/ so there's lots more info and photos there.

The car is very nearly complete, hoping to have it moving by the end of the week! Will try to post some more info and videos soon.

[EV_Builder]

@catphish you might want to consider 2 things. After welding drilling the shafts completely and press steel H7 8 or 10mm pen through it all or better send them off to Poland and get them back with new middle axles made to your distance and splines for 150euros excl. transportation.

[catphish]

@catphish you might want to consider 2 things. After welding drilling the shafts completely and press steel H7 8 or 10mm pen through it all or better send them off to Poland and get them back with new middle axles made to your distance and splines for 150euros excl. transportation.

There seem to be a few opinions about how best to complete the join. The options seem to be:
1) Just weld round the visible join.
2) Drill 4 shallow holes and plug weld.
3) Drill a single hole right through the join, insert and weld a pin

Options 2 and 3 should create a stronger joint at the expense of weakening the outer shaft.

I am indeed considering sending the prototype shafts to someone like this to remanufacture: https://berrisford.co.uk/product/custom ... ny-length/

Here they are, press fitted but not yet welded.

[EV_Builder]

1 gives you strength but the issue is from a tension point of view that you kinda have a "line" contact which means that if the axle isn't perfect inline, which it won't be, that the forces wony be even spread i fear.

4option:
Imagen milling a two slots of say 8mm into the hollow shaft.
(U style from above)
Now you increased welding length considerably but you also kinda grab the axle on 2 points so to speak. The weld will make sure the U doesn't open and it will join further the 2 axles. Now if it's enough I doubt it. But it's worth a try at your stage I guess. I mean Tesla's axles are solid, non tube, for a reason...

[remy_martian]

Fit tubing over the joint, spanning a couple of inches either side of the joint. Weld both ends of the tubing circumferentially with at least three passes - ensure you bevel the tubing ends to get a wide area for the weld to bite.

[catphish]

Fit tubing over the joint, spanning a couple of inches either side of the joint. Weld both ends of the tubing circumferentially with at least three passes - ensure you bevel the tubing ends to get a wide area for the weld to bite.

The shafts aren't the same diameter so I don't think it would be very easy to securely weld a sleeve

[Pete9008]

If you weld around the circumference then the failure mode that I'd be worried about is on the HAZ in the smaller shaft. It's a fairly nasty failure mode as the flailing end of the driveshaft can do a fair bit of damage to suspension before flying out. With that said I wouldn't be comfortable not welding around the circumference either as it is where all the strength is! With the welded shaft I would weld the circumference of the existing join but then fit a sleeve (machined to match both shaft diameters) over the top of the weld and then plug weld through multiple holes to secure it. That way you have the full strength of the current but joint, the added strength of the sleeve, minimised HAZ at the sleeve ends and the fact that if a weld fails the sleeve may hold it together while you slow down.

The trouble with option 2 & 3 (assuming that they are not combined with 1) is that they are asking the machined down section of the smaller shaft to take the full torque and I can't see that working. Bear in mind that it's the outer skin of the shaft that provides most of the strength. Performance shafts are often hollow to save weight (although they tend to be larger diameter too).

Whichever route you take, once it is in, I would paint a straight line down each shaft and do several hard low speed starts on a high grip surface and look for any signs of twisting on the shafts.

The other question is tyres, the better the tyre the more stress on the driveshafts. If you ever plan on doing track days with a sticky compound....

With the torque you have available from the Tesla motor I'd probably get custom shafts made - otherwise you will be worrying about it every time you use the power.

Note - I am no where near an expert and the above is just based on what I've seen and read up while considering similar mods on in the past.

Looking forward to more details on the finished car!

[Pete9008]

Just thought a little more about this - did you machine down the smaller shaft at all or just bore out the larger one? If the former then my comment on 2 and 3 above apply, if not they are probably not relevant. Where the larger shaft is bored out what wall thickness were you able to keep? Dependant on this thickness I would also be a little worried about the strength along the bored out hole, the wall here is largely unsupported even if you plug weld down to the smaller shaft. If the wall thickness is on the low side here I would definitely sleeve and also make sure that the sleeve extends past the base of the bored out section.

[EV_Builder]

He did pressfit it in so it won't come out easy there is no room for that either. It would simply slip and loose complete traction. I would U mill the 2 axles and then fill it up with weld on a high setting. Or drill some big holes and weld that up again. The welds then need to complete shear off in order to loose traction. In the end it's a matter of welding length between the 2 parts and the strength of the hollow tube in the first place.

[arber333]

He did pressfit it in so it won't come out easy there is no room for that either. It would simply slip and loose complete traction. I would U mill the 2 axles and then fill it up with weld on a high setting. Or drill some big holes and weld that up again. The welds then need to complete shear off in order to loose traction. In the end it's a matter of welding length between the 2 parts and the strength of the hollow tube in the first place.

There are manuals for this kind of splicing. If you manage to fit one shaft into another best method would be to weld it on the joint circumference additionaly drill out at least two 8mm holes 90deg apart into larger diameter shaft some 8cm from the joint edge. Drilling those into hardened shafts is a pain i know. Then spot weld them to the lower shaft. This greatly alleviates torque point stresses and makes joint behave as uniform metal piece.

[Uppertown]

Whatever method you use (And I won't add to the confusion by suggesting another;-) ) make sure you check the run out between centers after welding; a bent shaft will break the best of joints in no time.

As someone else has suggested a paint line down the length of the shaft will soon show if they are twisting (a bent shaft will USUALLY result in a hand numbing vibration)

[SuperV8]

I am indeed considering sending the prototype shafts to someone like this to remanufacture: https://berrisford.co.uk/product/custom ... ny-length/

I like this idea the best.
High torque & high traction will be finding the weakest link!

[EV_Builder]

I am indeed considering sending the prototype shafts to someone like this to remanufacture: https://berrisford.co.uk/product/custom ... ny-length/

I like this idea the best.
High torque & high traction will be finding the weakest link!

If you want the strongest shaft and there is no room in the origal shaft your are 100% right. Since joining will never be stronger then solid and original it's solid.

[Peter]

Considering when buying a secondhand OEM Tesla driveshaft (£200 - £250), then chopping and home brew welding etc against the price around £250 from Berrisford looks excellent and gives peace of mind.

[catphish]

Just thought a little more about this - did you machine down the smaller shaft at all or just bore out the larger one? If the former then my comment on 2 and 3 above apply, if not they are probably not relevant. Where the larger shaft is bored out what wall thickness were you able to keep? Dependant on this thickness I would also be a little worried about the strength along the bored out hole, the wall here is largely unsupported even if you plug weld down to the smaller shaft. If the wall thickness is on the low side here I would definitely sleeve and also make sure that the sleeve extends past the base of the bored out section.

To clarify, I left the smaller shaft as-is, and bored out the larger shaft only. The larger Tesla shaft was left with a radius of 6mm of hardened outer material. The joints is now welded (in the simplest manner).

Everything is now assembled and working, but I have a knocking under light acceleration and no load, not sure where it's coming from yet...

[catphish]

There are manuals for this kind of splicing. If you manage to fit one shaft into another best method would be to weld it on the joint circumference additionaly drill out at least two 8mm holes 90deg apart into larger diameter shaft some 8cm from the joint edge. Drilling those into hardened shafts is a pain i know. Then spot weld them to the lower shaft. This greatly alleviates torque point stresses and makes joint behave as uniform metal piece.

Thanks, this sounds reasonable. I didn't do this because I was confused by all the options and didn't want to do more harm than good making more holes. Will keep it in mind though!

[remy_martian]

Do two or three more staggered passes on those welds.

One weld bead is not enough and you do not want any undercut.

[Pete9008]

Looking good - not sounding quite as good though!

Is it possible that you are running out of plunge on one of the driveshafts? If you haven't already done so I'd remove the shocks and move the wheel through the full suspension travel and check that there is spare movement in the CVs. Other possibility is a bit of muck/swarf in one of the balls causing it bind slightly. Can you hear whereabouts the knock is coming from?

On the joints 6mm on the limit of what I'd consider acceptable, might be worth doing a few sums on torque capability of a 6mm wall tube vs the solid Vauxhall shaft? At the very minimum I'd sleeve it with the sleeve extending past the bored out section and onto the Vauxhall shaft and then drill and plug weld. It looks like you have the space and as arber333 says it would spread the loads into the shafts much better.

Having said that, once you are happy with the lengths and operation, I'd get custom shafts made.

[arber333]

I was tired when i was cutting the right shaft to length. Of course i cut it too long. Remember halfh shaft positions form a triangle with suspension arm and if you do not consider edge points of movement you may cut the shaft in fully extended position which will become too long when the weight is on the wheels. I had to cut it about further 3cm to stop binding the joint.

[EV_Builder]

If I'm right the shafts should be dimensioned in horizontal state then there should be couple of MM room each side. So not bottoming out. Don't forget the alignment adjustments on the wishbones.

If the wheel rises or drops the stroke in the joint can do it's thing. The Tesla side had quite some stroke...14mm?

The ratle has todo with load i think. While wining down, light regen, you don't hear it. What i think is that on fixed rpm with not allot of weight the algo constantly tries to match revs and if that jumps around it's heard. Basically the rpms aren't steady I think...

[catphish]

Thanks for all the pointers. I drove the car today! The noise I was previously worried about seems to be gone with the car properly loaded, but I will spend some time later really listening for everything to be sure everything is right.

I have 3 new problems to address, hopefully all fairly simple.
1) The brakes aren't bled properly, they're very spongy, I'm sure i can fix that, just need to spend a bit more time bleeding them properly.
2) I need a new brake bleed nipple. One of mine was seized and I destroyed it getting it out.
3) The SDU is cutting torque at 100% throttle. I guess I've made a mistake with tuning, either it's hitting a derate limit or I may have set the slip too high and voltage too low and it's stalling.

[EV_Builder]

very cool and very jealous...

[Bigpie]

That thing is going to bring the smiles.